Comprehensive Utilization of Steel Slag

Chapter 3

Abstract

detailed.

35

1. Introduction

Treatments and Recycling of

Elena Brandaleze, Edgardo Benavidez and Leandro Santini

Steelmaking plants continuously strive to reduce the environmental load in the

steelmaking process, resulting in the recycling of energy, water, and other byproducts. In this chapter, techniques for the treatment and recycling of metallurgical slags are described. Metallurgical slags are considered secondary raw materials and are used or added during the process to improve steelmaking practice. Steelmaking slag added into ladle slags makes it possible to minimize slag line wear. BOF-converter slags are also applied in buildup, foaming, or slag splashing practices carried out to prolong the lifespan of refractory lining. Also, EAF slags are commonly used to avoid refractory wear and decrease energy consumption. It is known that cement concrete is one of the most common building materials. Blast furnace crystallized slags are used in cement production, in different percentages. In this sense, understanding the properties of slags is a prerequisite to apply them in different functions. This chapter deals with the measurement and modeling of thermochemical properties of slags, thermophysical properties, and interproperty correlations. Different experimental tests applied in slag characterization are also

Keywords: slag, recycling, steelmaking, refractory wear, slag properties

In modern steel plants, the emphasis is placed simultaneously on quantity and quality. Energy consumption per ton of steel production is often considered a benchmark of operational efficiency. Steel production necessarily involves production of millions of tons of slag as well as waste gases containing harmful constituents such as carbon dioxide, dioxin, and furans. Safe disposal of slag and elimination of atmospheric pollution by waste gases are now a matter of serious concern in all steel producing countries. Developed countries are now laying tremendous emphasis on: (a) reduction in energy consumption per ton of steel produced and (b) sustainable environmental management. The most recent thrust is on more integrated green manufacturing and more intensive waste recycling for sustainable development. Efforts are on for economic use of all types of steel plant wastes, such as slag, dust, and flue gases [1]. Slag in ironmaking and steelmaking processes has several metallurgical functions such as preventing contamination by atmosphere, providing thermal insulation, and removing impurities in the liquid metal. Slag as a mixture of oxide has specific properties of melting behavior, viscosity, and surface tension, among others [2]. Optimal slag properties require: low thermal conductivity for

Metallurgical Slags

### Chapter 3

## Treatments and Recycling of Metallurgical Slags

Elena Brandaleze, Edgardo Benavidez and Leandro Santini

#### Abstract

Steelmaking plants continuously strive to reduce the environmental load in the steelmaking process, resulting in the recycling of energy, water, and other byproducts. In this chapter, techniques for the treatment and recycling of metallurgical slags are described. Metallurgical slags are considered secondary raw materials and are used or added during the process to improve steelmaking practice. Steelmaking slag added into ladle slags makes it possible to minimize slag line wear. BOF-converter slags are also applied in buildup, foaming, or slag splashing practices carried out to prolong the lifespan of refractory lining. Also, EAF slags are commonly used to avoid refractory wear and decrease energy consumption. It is known that cement concrete is one of the most common building materials. Blast furnace crystallized slags are used in cement production, in different percentages. In this sense, understanding the properties of slags is a prerequisite to apply them in different functions. This chapter deals with the measurement and modeling of thermochemical properties of slags, thermophysical properties, and interproperty correlations. Different experimental tests applied in slag characterization are also detailed.

Keywords: slag, recycling, steelmaking, refractory wear, slag properties

### 1. Introduction

In modern steel plants, the emphasis is placed simultaneously on quantity and quality. Energy consumption per ton of steel production is often considered a benchmark of operational efficiency. Steel production necessarily involves production of millions of tons of slag as well as waste gases containing harmful constituents such as carbon dioxide, dioxin, and furans. Safe disposal of slag and elimination of atmospheric pollution by waste gases are now a matter of serious concern in all steel producing countries. Developed countries are now laying tremendous emphasis on: (a) reduction in energy consumption per ton of steel produced and (b) sustainable environmental management. The most recent thrust is on more integrated green manufacturing and more intensive waste recycling for sustainable development. Efforts are on for economic use of all types of steel plant wastes, such as slag, dust, and flue gases [1]. Slag in ironmaking and steelmaking processes has several metallurgical functions such as preventing contamination by atmosphere, providing thermal insulation, and removing impurities in the liquid metal. Slag as a mixture of oxide has specific properties of melting behavior, viscosity, and surface tension, among others [2]. Optimal slag properties require: low thermal conductivity for

better thermal insulation, low diffusion coefficients to inhibit unwanted pickup from the atmosphere, and high absorption capacity for nonmetallic inclusion removal. Physicochemical properties of slag and molten metal directly affect the surface and interfacial properties in refining process of molten metal [2].

vessel after tapping. Slag with low FeO and high MgO is desirable. The practice is carried out with nitrogen injection through a lance at different heights. In this case,

Slag foaming is also applied in EAF to prevent the heat loss and to decrease the refractory wear. To improve the performance of these industrial practices and their applications, it is necessary to deeply understand the fundamental phenomena so as to determine slag's characteristics and physical properties required at process

Another type of slag that is produced in considerable quantity (ton/year) by the steelmaking industry is ladle slag. Because ladle slag is a premelted flux, when it is recycled in the steelmaking process, it is easy to be remelted. This type of slag has good physical properties, high inclusion absorptivity, and high sulfide capacity. Choi et al. [3] described two possible methods to recycle ladle slag: (a) by pouring molten ladle slag to another ladle, at time (taking advantage of the heat) and (b) by making a ladle slag ingot. The latter option mentioned is complex because of the unstable method used for making ingots. Ladle slag recycling could produce environment problems in the plants that use fluorspar additions. HF emissions generated increased F concentrations in the plant water and exhaust gas. However, it is relevant to highlight that ladle slag reuse promotes dephosphorization reaction at BOF and can substitute expensive steelmaking agents, and besides, the process can

To summarize, slag recycling requires the availability of detailed and precise information on their behavior, physical properties, and structural characteristics. This chapter is focused on the chemical composition, structural characteristics, thermal and physical properties, and behavior (at high temperature) of different slags used to protect refractories in BOF and EAF as recycling possibilities.

Longer lifespans of BOF lining and greater availability result in a reduction of costs per ton of liquid steel. Different steel plants, depending on their lay out, process conditions, and operation, have developed and implemented various techniques for protecting MgO-C refractory lining: brick patching, gunning, manual splashing, chemical splashing, slag coating, slag foaming, and slag splashing [1, 4]. In this chapter, two main slag practices are described: slag coating and slag foaming

The application of MgO saturated coating slags helps to reduce the impact of the BOF operation on the refractory lining. These slags form a protective layer on the bottom of BOF MgO-C bricks improving the lifespan of the lining. Slag fluidity and the physics and chemistry of the refractory-slag interaction are relevant to the design of these coating slags. The blowing practice, the end of blow temperature, the ratio of solid-to-liquid phases in the slag, its morphology, its particle size, and chemistry are determining factors for the required properties. Slag-refractory adherence mechanisms are analyzed, and measurements of slag fluidity at high temperature and other physical properties obtained by thermodynamic simulation (up to 1700°C) are informed. Slags of appropriate characteristics allow lining recovery, reducing corrosion damage, oxidation, and erosion of the refractory, as well as the impact of the charge, without altering the metallurgical function of the BOF. Slags used for this purpose need to be optimized and characterized [4].

some plants require special equipment installation.

Treatments and Recycling of Metallurgical Slags DOI: http://dx.doi.org/10.5772/intechopen.80595

conditions.

be more ecofriendly.

37

2. BOF slags recycling practices

considering experimental data and theoretical information.

2.1 BOF slags applied in slag coating practice

Slag is of great relevance in metallurgy processes for steel quality; however, during long years, it was considered an important waste together with the accumulation of refractories after use. This forces us to look for alternative uses to minimize the impact on the environment. A new concept considers to use the waste of one industry as a resource in another industry. One of the main applications that can be given to the slag is as recycled aggregate in the formulation of concrete or abrasive material applications. Nowadays, it is possible to consider the slag as a possible raw material for ceramics, road buildup, or cement production. The mentioned uses include an exhaustive control of the content of Ba, Cd, Cr, Mo, Ni, Pb, V, and Zn, in order to avoid contamination or air pollution. The content of sulfates or sulfides is also controlled to avoid the SO2 emissions. To avoid volumetric instability of the cement material, MgO content is determined.

The addition of blast furnace slag into cement avoids a part of limestone and coal extraction and makes it possible to diminish the CO2 emissions that cause environment pollution. It is important to have in mind that blast furnace slags present particular hydraulic properties. They are produced at high temperatures, and under fast-cooling rates, the structure obtained is amorphous. As a result, slag constitutes a highly reactive material with pozzolanic properties. On the contrary, at lowcooling rate, a crystalline structure with a considerable hardness is produced. In this case, slag constitutes a good raw material for cement production and also contributes with Fe addition to the clinker. A great part of the steel produced in the world is obtained through electric arc furnace (EAF), the process involves the use of scrap metal and reduces the CO2 emissions. EAF slags present great possibilities of recycling, similar to those of BOF slags.

Slags recycling in cement production, road buildup, or other applications (that involve soil contact) are subjected to important environmental requirements. The material must not present reactions or composition changes greater than 1% in a period of 100 years.

One of the biggest challenges for metallurgists is to recycle the slag directly in the steelmaking processes. The operation temperatures and aggressive conditions promote a rapid wear of the refractories of BOF converters and EAF furnaces. Modern LD converters are lined with MgO-C refractories. The presence of carbon controls slag penetration and chemical attack. The capacity of graphite to reduce wear is based upon its large wetting angle for oxide melts. Slags can penetrate the bricks only when the graphite is burnt away near the hot face owing to diffusion of oxygen in between flows during a campaign [1].

In BOF converters, different operation practices using slags as protection media are used to prolong the lifespan of lining refractory:


In the three cases, the slags require good physical properties (viscosity and surface tension) to achieve good protection results and an adequate slag adherence to MgO-C bricks. In the slag splashing technology, a portion of slag is retained in the

#### Treatments and Recycling of Metallurgical Slags DOI: http://dx.doi.org/10.5772/intechopen.80595

better thermal insulation, low diffusion coefficients to inhibit unwanted pickup from the atmosphere, and high absorption capacity for nonmetallic inclusion removal. Physicochemical properties of slag and molten metal directly affect the

Slag is of great relevance in metallurgy processes for steel quality; however, during long years, it was considered an important waste together with the accumulation of refractories after use. This forces us to look for alternative uses to minimize the impact on the environment. A new concept considers to use the waste of one industry as a resource in another industry. One of the main applications that can be given to the slag is as recycled aggregate in the formulation of concrete or abrasive material applications. Nowadays, it is possible to consider the slag as a possible raw material for ceramics, road buildup, or cement production. The mentioned uses include an exhaustive control of the content of Ba, Cd, Cr, Mo, Ni, Pb, V, and Zn, in order to avoid contamination or air pollution. The content of sulfates or sulfides is also controlled to avoid the SO2 emissions. To avoid volumetric instability of the

The addition of blast furnace slag into cement avoids a part of limestone and coal extraction and makes it possible to diminish the CO2 emissions that cause environment pollution. It is important to have in mind that blast furnace slags present particular hydraulic properties. They are produced at high temperatures, and under fast-cooling rates, the structure obtained is amorphous. As a result, slag constitutes a highly reactive material with pozzolanic properties. On the contrary, at lowcooling rate, a crystalline structure with a considerable hardness is produced. In this case, slag constitutes a good raw material for cement production and also contributes with Fe addition to the clinker. A great part of the steel produced in the world is obtained through electric arc furnace (EAF), the process involves the use of scrap metal and reduces the CO2 emissions. EAF slags present great possibilities of

Slags recycling in cement production, road buildup, or other applications (that involve soil contact) are subjected to important environmental requirements. The material must not present reactions or composition changes greater than 1% in a

One of the biggest challenges for metallurgists is to recycle the slag directly in the steelmaking processes. The operation temperatures and aggressive conditions promote a rapid wear of the refractories of BOF converters and EAF furnaces. Modern LD converters are lined with MgO-C refractories. The presence of carbon controls slag penetration and chemical attack. The capacity of graphite to reduce wear is based upon its large wetting angle for oxide melts. Slags can penetrate the bricks only when the graphite is burnt away near the hot face owing to diffusion of

In BOF converters, different operation practices using slags as protection media

• Slag splashing, which protects the bottom, the middle, and the upper parts of

In the three cases, the slags require good physical properties (viscosity and surface tension) to achieve good protection results and an adequate slag adherence to MgO-C bricks. In the slag splashing technology, a portion of slag is retained in the

• Slag coating or buildup, which protects the bottom part of the converter

• Slag foaming, which protects the refractories below the trunnion line

surface and interfacial properties in refining process of molten metal [2].

cement material, MgO content is determined.

Recovery and Utilization of Metallurgical Solid Waste

recycling, similar to those of BOF slags.

oxygen in between flows during a campaign [1].

the refractory lining.

36

are used to prolong the lifespan of lining refractory:

period of 100 years.

vessel after tapping. Slag with low FeO and high MgO is desirable. The practice is carried out with nitrogen injection through a lance at different heights. In this case, some plants require special equipment installation.

Slag foaming is also applied in EAF to prevent the heat loss and to decrease the refractory wear. To improve the performance of these industrial practices and their applications, it is necessary to deeply understand the fundamental phenomena so as to determine slag's characteristics and physical properties required at process conditions.

Another type of slag that is produced in considerable quantity (ton/year) by the steelmaking industry is ladle slag. Because ladle slag is a premelted flux, when it is recycled in the steelmaking process, it is easy to be remelted. This type of slag has good physical properties, high inclusion absorptivity, and high sulfide capacity. Choi et al. [3] described two possible methods to recycle ladle slag: (a) by pouring molten ladle slag to another ladle, at time (taking advantage of the heat) and (b) by making a ladle slag ingot. The latter option mentioned is complex because of the unstable method used for making ingots. Ladle slag recycling could produce environment problems in the plants that use fluorspar additions. HF emissions generated increased F concentrations in the plant water and exhaust gas. However, it is relevant to highlight that ladle slag reuse promotes dephosphorization reaction at BOF and can substitute expensive steelmaking agents, and besides, the process can be more ecofriendly.

To summarize, slag recycling requires the availability of detailed and precise information on their behavior, physical properties, and structural characteristics. This chapter is focused on the chemical composition, structural characteristics, thermal and physical properties, and behavior (at high temperature) of different slags used to protect refractories in BOF and EAF as recycling possibilities.

### 2. BOF slags recycling practices

Longer lifespans of BOF lining and greater availability result in a reduction of costs per ton of liquid steel. Different steel plants, depending on their lay out, process conditions, and operation, have developed and implemented various techniques for protecting MgO-C refractory lining: brick patching, gunning, manual splashing, chemical splashing, slag coating, slag foaming, and slag splashing [1, 4]. In this chapter, two main slag practices are described: slag coating and slag foaming considering experimental data and theoretical information.

#### 2.1 BOF slags applied in slag coating practice

The application of MgO saturated coating slags helps to reduce the impact of the BOF operation on the refractory lining. These slags form a protective layer on the bottom of BOF MgO-C bricks improving the lifespan of the lining. Slag fluidity and the physics and chemistry of the refractory-slag interaction are relevant to the design of these coating slags. The blowing practice, the end of blow temperature, the ratio of solid-to-liquid phases in the slag, its morphology, its particle size, and chemistry are determining factors for the required properties. Slag-refractory adherence mechanisms are analyzed, and measurements of slag fluidity at high temperature and other physical properties obtained by thermodynamic simulation (up to 1700°C) are informed. Slags of appropriate characteristics allow lining recovery, reducing corrosion damage, oxidation, and erosion of the refractory, as well as the impact of the charge, without altering the metallurgical function of the BOF. Slags used for this purpose need to be optimized and characterized [4].

Slag behavior at process temperatures depends on slag chemistry, melting behavior, viscosity, surface tension, fluidity, FeO content, and MgO saturation. In addition, solid and liquid phases of the slag (at practice temperatures) in the system have relevant influence on the adherence behavior. All these factors lead to/foster the achievement of a good slag layer on the surface of MgO-C bricks.

Experimental tests of physical properties as viscosity and surface tension of multicomponent systems at high temperatures (higher than 1500°C) are difficult to carry out due to the complexity of the process and the amount of time involved. The presence of impurities and possible reactions between the crucible material and the slag produces a transportation problem in the interface that can reduce the values of the properties and can occasionally modify wettability. These factors induce the development of mathematical models and thermodynamic simulation applications to predict the viscosity of a system as a function of slag chemistry [5–8]. The Urbain theoretical model is being one of those more used for the steelmaking slags [5], being the Urbain model one of the most widely used for industrial slags. The model estimates the viscosity of liquid silicates and alumino-silicates in function of chemical composition and describes temperature dependence of viscosity through the Weymann expression, Eq. (1):

$$\eta = \text{AT} \exp\left(\mathbf{10^3 B/T}\right) \tag{1}$$

where η is the viscosity in poise; T is the absolute temperature in K; and A and B are the parameters that depend on slag chemical composition (A is expressed in poise K�<sup>1</sup> and B in K), Eq. (2).

$$-\ln\text{A} = 0.2\text{€}9\text{\"B} + \text{11.6725} \tag{2}$$

A slag sample with FeO ≈ 18, MgO ≈ 11, CaO ≈ 43, Al2O3 ≈ 1.6, and SiO2 ≈ 17% wt. was characterized by different experimental tests. The melting behavior was determined by hot-stage microscopy (HSM). The critical temperatures obtained are Tinitial = 1398°C,Tsoftening = 1408°C,Themisphere = 1412°C, and Tfluidity = 1419°C. At 1600°C, the average of the contact angle measured was θaverage = 33°. Also, a good adherence behavior on MgO-C samples was obtained by means of dipping tests. Viscosity values estimated by the Urbain model and FactSage 7.2 at 1600°C for the slag were ηFSage = 0.29 poise/ηUrbain = 0.90 poise. The solid and liquid phases predicted (at 1600°C) by the Equilib module of the software are 92.25 g of a liquid

Slag SiO2 (%)

Group A (18 < FeO < 22)

Group B (22 < FeO < 25)

Group C (25 < FeO < 30)

Group D (FeO > 30)

Group E (FeO < 18)

End of blow slag chemistry.

Table 1.

39

CaO (%)

Treatments and Recycling of Metallurgical Slags DOI: http://dx.doi.org/10.5772/intechopen.80595

> FeO (%)

MgO (%)

MnO (%)

1 15.9 44.3 19.6 10.2 6.3 0.8 2.8 0.06 0.25 0.78 2 15.4 47.0 18.7 8.4 5.9 1.5 2.7 0.08 0.26 0.80 3 14.8 45.3 21.6 8.4 6.3 1.0 2.4 0.06 0.24 0.75 4 15.3 45.7 20.7 7.6 6.2 1.9 2.5 0.08 0.25 0.81 5 15.3 45.1 21.0 7.6 6.4 2.1 2.5 0.07 0.25 0.83

6 14.2 44.1 22.5 8.8 6.3 1.4 2.4 0.07 0.23 0.75 7 14.7 43.9 22.5 7.9 6.4 1.4 2.7 0.07 0.23 0.77 8 14.0 44.3 24.4 7.5 5.8 1.6 2.5 0.08 0.23 0.75 9 15.3 43.8 23.7 7.2 6.2 1.6 2.5 0.08 0.23 0.80 10 14.4 44.2 24.1 7.2 6.1 0.9 2.6 0.07 0.22 0.74

11 13.2 44.6 25.6 7.5 5.6 1.2 2.3 0.08 0.21 0.70 12 13.8 43.7 26.3 6.9 5.5 1.2 2.1 0.09 0.22 0.73 13 12.1 44.3 25.8 7.9 5.7 1.6 2.2 0.08 0.21 0.68 14 13.9 44.0 25.3 6.9 6.2 1.2 2.5 0.07 0.22 0.73 15 13.4 43.7 26.0 6.9 5.9 1.6 2.3 0.08 0.21 0.73

16 12.7 39.7 32.1 7.6 5.8 0.8 2.2 0.08 0.18 0.67 17 10.5 32.1 39.9 8.5 6.0 0.8 1.8 0.07 0.15 0.59 18 10.5 42.3 31.4 6.5 5.6 1.2 1.9 0.09 0.18 0.60 19 12.0 40.0 32.5 6.4 5.6 0.9 2.0 0.08 0.17 0.65 20 11.5 39.9 33.6 6.7 5.3 0.7 1.8 0.07 0.17 0.62

21 18.5 45.2 16.7 7.8 6.8 1.0 3.1 0.06 0.29 0.90 22 13.0 48.2 16.4 9.8 6.0 1.7 2.8 0.09 0.26 0.72 23 18.2 49.9 14.1 6.8 5.6 1.6 3.3 0.09 0.31 0.91 24 17.9 49.0 15.3 6.8 5.9 1.8 3.0 0.10 0.30 0.92 25 17.7 49.1 16.1 6.4 5.8 1.7 2.9 0.10 0.30 0.90

Al2O3 (%)

P2O5 (%)

S (%)

ηFS (poise)

ηUrbain (poise)

The Urbain model [5] classified the oxides into three groups:


In this chapter, viscosity values of end-of-blow slags were estimated taking into account the Urbain model and applying the viscosity module for melts of FactSage 7.2 software [6]. It is important to mention that during the last year, large thermodynamic databases of multicomponent oxide systems have been developed, and parameters have been optimized in order to reproduce all reliable experimental data within experimental errors. The information obtained through FactSage 7.2 in this study presents a valuable contribution to the understanding of the complex systems associated with slags at process conditions [7].

The industrial end-of-blow slags selected for this study were divided into five groups with different FeO contents: A (18 < FeO < 22), B (22 < FeO < 25), C (25 < FeO < 30), D (FeO>30) and E (FeO<18). Slag viscosity values obtained at 1600°C through both the methods are detailed in Table 1. In Figure 1, a comparison of the viscosity values obtained for slags A, B, C, D, and E shows that slags of the E group, with FeO content lower than 18 %wt. and a binary index (BI) 2.88, present the highest viscosities. In Figure 2, it is possible to evaluate the impact of slag FeO content on the viscosity evolution.


Treatments and Recycling of Metallurgical Slags DOI: http://dx.doi.org/10.5772/intechopen.80595

Slag behavior at process temperatures depends on slag chemistry, melting behavior, viscosity, surface tension, fluidity, FeO content, and MgO saturation. In addition, solid and liquid phases of the slag (at practice temperatures) in the system have relevant influence on the adherence behavior. All these factors lead to/foster the achievement of a good slag layer on the surface of

Experimental tests of physical properties as viscosity and surface tension of multicomponent systems at high temperatures (higher than 1500°C) are difficult to carry out due to the complexity of the process and the amount of time involved. The presence of impurities and possible reactions between the crucible material and the slag produces a transportation problem in the interface that can reduce the values of the properties and can occasionally modify wettability. These factors induce the development of mathematical models and thermodynamic simulation applications to predict the viscosity of a system as a function of slag chemistry [5–8]. The Urbain theoretical model is being one of those more used for the steelmaking slags [5], being the Urbain model one of the most widely used for industrial slags. The model estimates the viscosity of liquid silicates and alumino-silicates in function of chemical composition and describes temperature dependence of viscos-

where η is the viscosity in poise; T is the absolute temperature in K; and A and B are the parameters that depend on slag chemical composition (A is expressed in

The Urbain model [5] classified the oxides into three groups:

• Modifiers: XM ¼ XCaO þ XMgO þ XNa2O þ XK2O þ 3XCaF2 þ XFeO þ XMnOþ

In this chapter, viscosity values of end-of-blow slags were estimated taking into account the Urbain model and applying the viscosity module for melts of FactSage 7.2 software [6]. It is important to mention that during the last year, large thermodynamic databases of multicomponent oxide systems have been developed, and parameters have been optimized in order to reproduce all reliable experimental data within experimental errors. The information obtained through FactSage 7.2 in this study presents a valuable contribution to the understanding of the complex systems

The industrial end-of-blow slags selected for this study were divided into five

groups with different FeO contents: A (18 < FeO < 22), B (22 < FeO < 25), C (25 < FeO < 30), D (FeO>30) and E (FeO<18). Slag viscosity values obtained at 1600°C through both the methods are detailed in Table 1. In Figure 1, a comparison of the viscosity values obtained for slags A, B, C, D, and E shows that slags of the E group, with FeO content lower than 18 %wt. and a binary index (BI) 2.88, present the highest viscosities. In Figure 2, it is possible to evaluate the impact of slag FeO

<sup>η</sup> <sup>¼</sup> AT exp 10<sup>3</sup> <sup>B</sup>=<sup>T</sup> (1)

�ln A ¼ 0:2693B þ 11:6725 (2)

MgO-C bricks.

ity through the Weymann expression, Eq. (1):

Recovery and Utilization of Metallurgical Solid Waste

poise K�<sup>1</sup> and B in K), Eq. (2).

2XTiO2 þ 2XZrO2

• Glass formers: XG ¼ XSiO2 þ X<sup>P</sup>2O5

• Anfoters: XA ¼ XAl2O3 þ XFe2O3 þ XB2O3

associated with slags at process conditions [7].

content on the viscosity evolution.

38

Table 1.

End of blow slag chemistry.

A slag sample with FeO ≈ 18, MgO ≈ 11, CaO ≈ 43, Al2O3 ≈ 1.6, and SiO2 ≈ 17% wt. was characterized by different experimental tests. The melting behavior was determined by hot-stage microscopy (HSM). The critical temperatures obtained are Tinitial = 1398°C,Tsoftening = 1408°C,Themisphere = 1412°C, and Tfluidity = 1419°C. At 1600°C, the average of the contact angle measured was θaverage = 33°. Also, a good adherence behavior on MgO-C samples was obtained by means of dipping tests. Viscosity values estimated by the Urbain model and FactSage 7.2 at 1600°C for the slag were ηFSage = 0.29 poise/ηUrbain = 0.90 poise. The solid and liquid phases predicted (at 1600°C) by the Equilib module of the software are 92.25 g of a liquid

of liquid phase (L1), promoting optimum viscosity and contact angle values that favor the adherence of slag on MgO-C bricks on the bottom of the converter. However, slags with higher FeO content promote the increase of the liquid phase proportion (L1) with chemical composition changes that produce disadvantages regarding wettability. Slags with the chemical and physical properties mentioned are applied in BOF slag coating practice in the industry with good results increasing

Slag foaming constitutes another alternative to use the converter slags to protect MgO-C bricks below the trunnion line [8, 10]. It is important to take into account that in order to enhance the performance of this industrial practice, it is necessary to understand deeply the associated fundamental phenomena. Along the steel conversion process, the oxygen blown is mostly combined with elements dissolved in the melt. The reaction products are oxides, which are finally incorporated into the slag. If a carbonaceous material is added after blow, C reacts with FeO and generates

CO for foaming is also produced by decarburization of the metal given by

Gas bubbles in the slag foam could be small or large. The size of the bubbles determines the foam behavior. Foam with small bubbles is dense avoiding the risk of slopping and promoting good slag adherence to the refractory surface. On the contrary, large bubbles like soap generate unstable foam and the likelihood of slopping. Two types of foams can be distinguished: (i) foams initially formed by spherical bubbles that are separated by thick films of liquid and (ii) polyhedral foams in which the bubbles are deformed because of drainage of the liquid film [9–12]. Drainage phenomena decrease the thickness of the liquid separating film to

As it is known, converter slags are an extremely complex mix of oxides that determine the slag physical properties such as viscosity, density, surface tension, and others. Therefore, accurate viscosity values are essential for the optimization and improvement of metallurgical processes. Experimental measurements have difficulties associated with the high temperature needed (or the high melting point of some slags). Consequently, an alternative is the application of theoretical models to estimate the viscosity and surface tension, as a function of temperature, on the

As it was already mentioned, viscosity is considerably affected by FeO content. If the FeO increases in the slag, the viscosity decreases and causes foam bubbles to drain more rapidly, resulting in foam decay. Hence, there is a critical FeO content below which foaming increases and above which the foam is less stable. Surface tension consists in a physical property that depends principally on the surface and not on the bulk. This is affected by the concentration of surfactants and the chemical activity of the surface active component, which determines the surface active concentration in the surface layer [15]. Both properties (viscosity and surface tension) are necessary to estimate the foaming index Σ and to increase the knowledge about this practice. Different expressions have been proposed for

C injected ð Þþ ð Þ! FeO Fe þ CO (3)

C in metal ð Þþ ½ O2 ! CO (4)

the lifespan of the lining and protecting the bottom of the converter.

2.2 BOF slags used in foaming practice

Treatments and Recycling of Metallurgical Slags DOI: http://dx.doi.org/10.5772/intechopen.80595

CO, Eq. (3), causing slag foaming.

values lower than 1 μm.

basis of slag chemical compositions [13, 14].

Eq. (4):

41

Figure 1. Comparison of viscosity values of slags for groups A, B, C, D, and E with different FeO content.

Figure 2. Influence of iron oxide content on viscosity at 1600°C.

phase L1 with a chemical composition: 4.70% MgO, 17.4% FeO, 6.47% MnO, 18.42% SiO2, 44.87% CaO, 2.16% Al2O3, 0.98% Fe2O3, 3.21% Ca3(PO4)2, 0.40% Mg3(PO4)2, and 1.12% Fe3(PO4)2 and two solid phases: 6.4 g of MgO and 0.33 g of Fe (bcc).

For slags with FeO ≈ 25.8%wt, MgO ≈ 7%wt., CaO ≈ 44%wt., Al2O3 ≈ 1%wt., and SiO2 ≈ 14%wt., the liquid phase L1 increases up to 97 g, and the chemical composition is as follows: 4.33% MgO, 24.2% FeO, 6.16% MnO, 14.45% SiO2, 43.8% CaO, 1.03% Al2O3, 1.23% Fe2O3, 2.82% Ca3(PO4)2, 0.33% Mg3(PO4)2, and 1.40% Fe3(PO4)2. The solid phases include 2.66 g of MgO and 0.44 g of Fe (bcc).

On the basis of the information obtained, it is possible to conclude that slags with 18% FeO at 1600°C present the adequate quantity and chemical composition Treatments and Recycling of Metallurgical Slags DOI: http://dx.doi.org/10.5772/intechopen.80595

of liquid phase (L1), promoting optimum viscosity and contact angle values that favor the adherence of slag on MgO-C bricks on the bottom of the converter. However, slags with higher FeO content promote the increase of the liquid phase proportion (L1) with chemical composition changes that produce disadvantages regarding wettability. Slags with the chemical and physical properties mentioned are applied in BOF slag coating practice in the industry with good results increasing the lifespan of the lining and protecting the bottom of the converter.

#### 2.2 BOF slags used in foaming practice

Slag foaming constitutes another alternative to use the converter slags to protect MgO-C bricks below the trunnion line [8, 10]. It is important to take into account that in order to enhance the performance of this industrial practice, it is necessary to understand deeply the associated fundamental phenomena. Along the steel conversion process, the oxygen blown is mostly combined with elements dissolved in the melt. The reaction products are oxides, which are finally incorporated into the slag. If a carbonaceous material is added after blow, C reacts with FeO and generates CO, Eq. (3), causing slag foaming.

$$\text{C(injected)} + (\text{FeO}) \rightarrow \text{Fe} + \text{CO} \tag{3}$$

CO for foaming is also produced by decarburization of the metal given by Eq. (4):

$$\text{C(in metal)} + \text{M}\_2\text{O}\_2 \rightarrow \text{CO} \tag{4}$$

Gas bubbles in the slag foam could be small or large. The size of the bubbles determines the foam behavior. Foam with small bubbles is dense avoiding the risk of slopping and promoting good slag adherence to the refractory surface. On the contrary, large bubbles like soap generate unstable foam and the likelihood of slopping. Two types of foams can be distinguished: (i) foams initially formed by spherical bubbles that are separated by thick films of liquid and (ii) polyhedral foams in which the bubbles are deformed because of drainage of the liquid film [9–12]. Drainage phenomena decrease the thickness of the liquid separating film to values lower than 1 μm.

As it is known, converter slags are an extremely complex mix of oxides that determine the slag physical properties such as viscosity, density, surface tension, and others. Therefore, accurate viscosity values are essential for the optimization and improvement of metallurgical processes. Experimental measurements have difficulties associated with the high temperature needed (or the high melting point of some slags). Consequently, an alternative is the application of theoretical models to estimate the viscosity and surface tension, as a function of temperature, on the basis of slag chemical compositions [13, 14].

As it was already mentioned, viscosity is considerably affected by FeO content. If the FeO increases in the slag, the viscosity decreases and causes foam bubbles to drain more rapidly, resulting in foam decay. Hence, there is a critical FeO content below which foaming increases and above which the foam is less stable. Surface tension consists in a physical property that depends principally on the surface and not on the bulk. This is affected by the concentration of surfactants and the chemical activity of the surface active component, which determines the surface active concentration in the surface layer [15]. Both properties (viscosity and surface tension) are necessary to estimate the foaming index Σ and to increase the knowledge about this practice. Different expressions have been proposed for

phase L1 with a chemical composition: 4.70% MgO, 17.4% FeO, 6.47% MnO, 18.42% SiO2, 44.87% CaO, 2.16% Al2O3, 0.98% Fe2O3, 3.21% Ca3(PO4)2, 0.40% Mg3(PO4)2, and 1.12% Fe3(PO4)2 and two solid phases: 6.4 g of MgO and 0.33 g of Fe (bcc). For slags with FeO ≈ 25.8%wt, MgO ≈ 7%wt., CaO ≈ 44%wt., Al2O3 ≈ 1%wt., and SiO2 ≈ 14%wt., the liquid phase L1 increases up to 97 g, and the chemical composition is as follows: 4.33% MgO, 24.2% FeO, 6.16% MnO, 14.45% SiO2, 43.8% CaO, 1.03% Al2O3, 1.23% Fe2O3, 2.82% Ca3(PO4)2, 0.33% Mg3(PO4)2, and 1.40% Fe3(PO4)2. The solid phases include 2.66 g of MgO and 0.44 g of Fe (bcc).

Comparison of viscosity values of slags for groups A, B, C, D, and E with different FeO content.

Recovery and Utilization of Metallurgical Solid Waste

Figure 2.

40

Figure 1.

Influence of iron oxide content on viscosity at 1600°C.

On the basis of the information obtained, it is possible to conclude that slags with 18% FeO at 1600°C present the adequate quantity and chemical composition foaming index Σ. In this study, Eq. (5) detailed by Fruehan and Matsura [16], is considered:

$$\Sigma = \mathbf{115} \frac{\mu^{1/2}}{\sigma^{0.2} \rho D\_B^{0.9}} \tag{5}$$

where DB, μ, ρ, and σ are the foam bubble diameter, slag viscosity, slag density, and slag surface tension, respectively.

Another point of interest is the foam life time, because it can vary greatly depending on the surfactant compounds present. Transient foams last for a few seconds, while stable foams have prolonged shelf life [12]. In this chapter, results of 16 BOF slags characterized for foaming practice are informed. Slag viscosity and surface tension were determined by theoretical models in order to establish the foaming index applying Eq. (5). The Urbain model [5] and Zaharia, Sahajwalla and Khanna model [17] were used to determine viscosity and surface tension, respectively. The results were completed with information about the thermal behavior of the slags obtained by hot-stage microscopy (HSM). Also, based on the slag chemical compositions, the isothermal solubility diagram (ISD) was applied in order to predict a good foaming behavior and capability of refractory protection.

Another contribution of this work is the information concerning different carbonaceous materials used to foam BOF slags. Three materials were studied considering physicochemical properties and structural aspects. The results were correlated with the information of the slag characterization.

Table 2 details the chemical composition of the BOF slags selected for the study in order to improve the foaming process. Based on the slag chemical composition, the binary basicity index (IB2) and ternary basicity index (IB3) are calculated to predict foamability of the slags applying ISD (see Table 3). The values of IB2


indicate that the slags are saturated in MgO and are compatible with refractory lining. All the slags were classified into three ternary basicity index (IB3) ranges: 1.9 > IB3 > 2.29, 2.29 > IB3 > 2.74, and 2.74 > IB3 > 3 and then placed in ISD (%MgO-

Slag IB2 IB3 η (1550°C) (Poise) γ (1550°C) (mN/m) ΣDb = 0.015 m ΣDb = 0.005 m 1 3.05 2.51 1.14 665 4.97 14.97 2 3.17 2.62 1.17 648 5.17 15.57 3 3.45 2.85 1.04 646 4.88 14.72 4 3.51 3.00 1.06 642 4.96 14.96 5 2.62 2.38 1.20 638 5.32 16.02 6 2.32 2.01 1.41 630 5.84 17.58 7 3.23 2.74 1.03 625 5.03 15.15 8 2.57 2.18 1.40 630 5.82 17.52 9 2.63 2.31 1.29 621 5.66 17.06 10 2.96 2.56 1.12 625 5.24 15.79 11 3.13 2.57 1.07 623 5.14 15.49 12 2.78 2.44 1.14 619 5.34 16.09 13 3.01 2.50 1.10 627 5.18 15.59 14 2.85 2.45 1.19 616 5.48 16.52 15 2.27 1.90 1.61 617 6.37 19.18 16 2.63 2.29 1.34 618 5.80 17.47

As it is known, a creamy slag is the optimum condition to obtain the good foamability described by Pretorious [18]. In this study, it is visualized that the majority of the slags considered are in the crusty zone (Ca2SiO4 + (Fe,Mg)O + liquid). Only four slags (E1, E10, E11, and E14) with IB3 2.5 are near the creamy zone ((Fe,Mg)O + liquid; see Figure 3). Nevertheless, when ISD includes the % MnO, the same four slags (E1, E10, E11 and E14) are moved toward the right

%FeO).

43

Figure 3.

Table 3.

Basicity index, viscosity, surface tension and foaming index values.

Treatments and Recycling of Metallurgical Slags DOI: http://dx.doi.org/10.5772/intechopen.80595

ISD (%MgO-%FeO) for three ternary basicity index ranges.

#### Table 2.

Chemical composition of foaming slags.


Treatments and Recycling of Metallurgical Slags DOI: http://dx.doi.org/10.5772/intechopen.80595

#### Table 3.

foaming index Σ. In this study, Eq. (5) detailed by Fruehan and Matsura [16], is

<sup>Σ</sup> <sup>¼</sup> <sup>115</sup> <sup>μ</sup>1=<sup>2</sup>

Another point of interest is the foam life time, because it can vary greatly depending on the surfactant compounds present. Transient foams last for a few seconds, while stable foams have prolonged shelf life [12]. In this chapter, results of 16 BOF slags characterized for foaming practice are informed. Slag viscosity and surface tension were determined by theoretical models in order to establish the foaming index applying Eq. (5). The Urbain model [5] and Zaharia, Sahajwalla and Khanna model [17] were used to determine viscosity and surface tension, respectively. The results were completed with information about the thermal behavior of the slags obtained by hot-stage microscopy (HSM). Also, based on the slag chemical compositions, the isothermal solubility diagram (ISD) was applied in order to pre-

dict a good foaming behavior and capability of refractory protection.

with the information of the slag characterization.

σ0:2ρD0:<sup>9</sup> B

where DB, μ, ρ, and σ are the foam bubble diameter, slag viscosity, slag density,

Another contribution of this work is the information concerning different carbonaceous materials used to foam BOF slags. Three materials were studied considering physicochemical properties and structural aspects. The results were correlated

Table 2 details the chemical composition of the BOF slags selected for the study in order to improve the foaming process. Based on the slag chemical composition, the binary basicity index (IB2) and ternary basicity index (IB3) are calculated to predict foamability of the slags applying ISD (see Table 3). The values of IB2

Slag % SiO2 %CaO % Al2O3 %MgO %FeO %MnO %P2O5 %S 1 13.96 42.60 3.04 12.39 22.18 5.96 1.70 0.11 2 13.55 42.97 2.89 8.58 23.56 5.31 1.79 0.09 3 12.31 42.45 2.60 8.28 25.79 7.76 1.76 0.10 4 13.12 46.10 2.26 8.95 21.46 7.06 1.86 0.09 5 16.20 42.41 1.63 10.83 20.71 6.64 1.87 0.07 6 18.09 42.02 2.79 10.08 19.99 6.79 1.71 0.08 7 12.74 41.13 2.25 10.96 26.40 5.79 1.61 0.06 8 17.23 44.32 3.13 9.43 19.15 5.47 2.08 0.09 9 16.74 44.02 2.34 8.66 20.47 7.73 2.04 0.11 10 13.84 40.95 2.14 7.99 25.65 8.33 1.81 0.09 11 12.21 38.19 2.62 7.20 29.55 7.68 1.77 0.09 12 14.47 40.16 1.99 8.26 28.34 5.79 1.60 0.07 13 13.03 39.23 2.67 8.32 26.22 9.96 1.66 0.10 14 14.91 42.47 2.46 9.52 24.05 5.41 1.78 0.09 15 19.68 44.61 3.86 9.47 17.20 5.28 1.96 0.09 16 17.15 45.13 2.57 8.07 19.95 6.67 1.92 0.09

(5)

considered:

Table 2.

42

Chemical composition of foaming slags.

and slag surface tension, respectively.

Recovery and Utilization of Metallurgical Solid Waste

Basicity index, viscosity, surface tension and foaming index values.

Figure 3. ISD (%MgO-%FeO) for three ternary basicity index ranges.

indicate that the slags are saturated in MgO and are compatible with refractory lining. All the slags were classified into three ternary basicity index (IB3) ranges: 1.9 > IB3 > 2.29, 2.29 > IB3 > 2.74, and 2.74 > IB3 > 3 and then placed in ISD (%MgO- %FeO).

As it is known, a creamy slag is the optimum condition to obtain the good foamability described by Pretorious [18]. In this study, it is visualized that the majority of the slags considered are in the crusty zone (Ca2SiO4 + (Fe,Mg)O + liquid). Only four slags (E1, E10, E11, and E14) with IB3 2.5 are near the creamy zone ((Fe,Mg)O + liquid; see Figure 3). Nevertheless, when ISD includes the % MnO, the same four slags (E1, E10, E11 and E14) are moved toward the right

Figure 4. ISD (%MgO-FeO + %MnO) for IB3 = 2.5.

showing the MnO effect (Figure 4). MgO content in the slags mentioned is between 7.2 and 12.4%.

Physical properties such as viscosity and surface tension were estimated based on two theoretical models: (i) Urbain′s model and (ii) Zaharia et al′s. model, respectively, in order to predict the foaming index (Σ) at 1550°C (see Table 2). Two different diameters (DB) of bubbles were considered in the Σ calculus: 0.015 m and 0.005 m. The results obtained are also detailed in Table 3. For slags (E1, E10, E11, and E14) with good foamability properties, the viscosity (η) values are between 1.07 and 1.19 poise and the surface tension between 616 and 665 mN/m, at 1550°C. The results are in agreement with Pretorious [18], who suggests low or medium values of surface tension in the slag for good foaming behavior. At 1550°C, the predicted average foaming index values for two bubble diameters (DB = 0.015 m and DB = 0.005 m) are 5.2 and 15.7, respectively. The content of %FeO in these four slags is between 22 and 30% and of %MnO between 5.4 and 8.3%. This information represents a good starting point to optimize the BOF foaming industrial practice. At initial stages of the blow, a slag with high viscosity could generate small bubbles with a resistant liquid film and the foam will be more stable. The correlation between IB3 and Σ shows that the foaming index decreases (slightly) as the basicity index increases (Figure 5).

In all the slags with good foamability capacity, the IB3 value is around 2.5. It was observed that when the bubbles present a DB = 0.005 mm (small size), MnO content (for MnO < 8%) results in random foaming index values compared to the effect of FeO content. The highest foaming index Σ was obtained for slag E15 with 19.68% SiO2, 17.20% FeO, 9.47% MgO, and 5.28% MnO. FeO content in the slag constitutes a variable that enables to control slag foaming. The study shows the sensibility of viscosity and surface tension, regarding FeO and MnO contents. Also, the higher the viscosity the higher the foaming index.

foaming) slags are between 1345 and 1380°C. However, for Af slags (after foaming),

Average critical temperature values (melting behavior) of the slags before and after foaming practice.

During slag foaming, when carbon is injected into the slags, gas bubbles are formed around the carbonaceous particles. It is necessary to take into consideration that different carbonaceous materials could produce different impact on slag foaming. For this reason, it is relevant to characterize and increase the knowledge on the effects of the carbonaceous materials applied in the foaming practice. Chemical and structural characteristics of three carbonaceous materials were studied. In Table 4, results of the chemical characteristics of carbonaceous materials are informed. Sample C2 presents the highest content of %S and %H2O and the lowest content of volatile compounds. Ash content is around 11% in materials C1 and C2 (typically in metallurgical cokes). Nevertheless, material C3 contains very low percentage of ash because it is a petroleum coke. Moreover, it presents the highest

an increase ≈ 3% of critical temperatures was determined.

Figure 5.

Figure 6.

45

Incidence of IB3 on foaming index Σ.

Treatments and Recycling of Metallurgical Slags DOI: http://dx.doi.org/10.5772/intechopen.80595

carbon content. Sulfur content is similar in all samples.

Slag samples, obtained pre (Bf) and post (Af) foaming practice, were characterized. The melting behavior was determined by hot-stage microscopy (HSM). Figure 6 shows the average critical temperatures: softening temperature (Ts), hemisphere temperature (Th), and fluidity temperature (Tf) of the samples.

It is worth noting that critical temperatures in slag samples increase after the foaming practice. These results indicate a dynamic evolution of the slag chemical composition during the practice. Average critical temperatures range for Bf (before Treatments and Recycling of Metallurgical Slags DOI: http://dx.doi.org/10.5772/intechopen.80595

Figure 5. Incidence of IB3 on foaming index Σ.

showing the MnO effect (Figure 4). MgO content in the slags mentioned is between

Physical properties such as viscosity and surface tension were estimated based

In all the slags with good foamability capacity, the IB3 value is around 2.5. It was

Slag samples, obtained pre (Bf) and post (Af) foaming practice, were character-

observed that when the bubbles present a DB = 0.005 mm (small size), MnO content (for MnO < 8%) results in random foaming index values compared to the effect of FeO content. The highest foaming index Σ was obtained for slag E15 with 19.68% SiO2, 17.20% FeO, 9.47% MgO, and 5.28% MnO. FeO content in the slag constitutes a variable that enables to control slag foaming. The study shows the sensibility of viscosity and surface tension, regarding FeO and MnO contents. Also,

ized. The melting behavior was determined by hot-stage microscopy (HSM). Figure 6 shows the average critical temperatures: softening temperature (Ts), hemisphere temperature (Th), and fluidity temperature (Tf) of the samples. It is worth noting that critical temperatures in slag samples increase after the foaming practice. These results indicate a dynamic evolution of the slag chemical composition during the practice. Average critical temperatures range for Bf (before

the higher the viscosity the higher the foaming index.

on two theoretical models: (i) Urbain′s model and (ii) Zaharia et al′s. model, respectively, in order to predict the foaming index (Σ) at 1550°C (see Table 2). Two different diameters (DB) of bubbles were considered in the Σ calculus: 0.015 m and 0.005 m. The results obtained are also detailed in Table 3. For slags (E1, E10, E11, and E14) with good foamability properties, the viscosity (η) values are between 1.07 and 1.19 poise and the surface tension between 616 and 665 mN/m, at 1550°C. The results are in agreement with Pretorious [18], who suggests low or medium values of surface tension in the slag for good foaming behavior. At 1550°C, the predicted average foaming index values for two bubble diameters (DB = 0.015 m and DB = 0.005 m) are 5.2 and 15.7, respectively. The content of %FeO in these four slags is between 22 and 30% and of %MnO between 5.4 and 8.3%. This information represents a good starting point to optimize the BOF foaming industrial practice. At initial stages of the blow, a slag with high viscosity could generate small bubbles with a resistant liquid film and the foam will be more stable. The correlation between IB3 and Σ shows that the foaming index decreases (slightly) as the basicity

7.2 and 12.4%.

ISD (%MgO-FeO + %MnO) for IB3 = 2.5.

Recovery and Utilization of Metallurgical Solid Waste

Figure 4.

index increases (Figure 5).

44

Figure 6. Average critical temperature values (melting behavior) of the slags before and after foaming practice.

foaming) slags are between 1345 and 1380°C. However, for Af slags (after foaming), an increase ≈ 3% of critical temperatures was determined.

During slag foaming, when carbon is injected into the slags, gas bubbles are formed around the carbonaceous particles. It is necessary to take into consideration that different carbonaceous materials could produce different impact on slag foaming. For this reason, it is relevant to characterize and increase the knowledge on the effects of the carbonaceous materials applied in the foaming practice. Chemical and structural characteristics of three carbonaceous materials were studied. In Table 4, results of the chemical characteristics of carbonaceous materials are informed. Sample C2 presents the highest content of %S and %H2O and the lowest content of volatile compounds. Ash content is around 11% in materials C1 and C2 (typically in metallurgical cokes). Nevertheless, material C3 contains very low percentage of ash because it is a petroleum coke. Moreover, it presents the highest carbon content. Sulfur content is similar in all samples.


Table 4.

Chemical characteristics of carbonaceous materials.

Furthermore, the ash content of materials C1 and C2 allows predicting rapid gas

Based on these results, it is possible to confirm that the evolution of properties (viscosity and surface tension) of BOF slags during the operation represents the key to obtain the best aptitude for foaming practice, avoiding the risk of slopping. High viscosity is perhaps the most obvious factor in the stabilization of BOF-converter foams, and it retards the rate of drainage in the films of the bubbles. Nevertheless, surface tension is also a relevant physical property that should be taken into account to predict foam behavior. Both properties, high viscosity and surface tension, are determined by the chemical composition and the evolution of the slag at process conditions. Carbonaceous materials also exert an effect in the foaming practice; it is possible to recommend the addition of petroleum coke (material C3) in the foaming practice, because of its ash low content, high proportion of large pores, and higher

Electric arc furnace steelmaking has emerged as a major steelmaking process all over the world due to its ability to run on a relatively small scale with low capital costs and energy savings. Steel scrap is the preferred metallic charge material, and sponge iron is also used regularly in most plants in order to dilute tramp elements introduced through the scrap [1, 17]. The growth of the arc furnace-based steel industry has been encouraged by modern arc furnaces of large capacity and ultrahigh power, electrical efficiency improvement, and metallurgical efficiency through oxygen lancing or the co-jet technology. In conventional EAF steelmaking, natural gas is generally used as a supplementary energy source. Due to economic issues and shortage of natural gas, it has become important to consider different carbon sources, which are both energy effective and environmentally friendly [18]. In addition, the decrease of refractory consumption is a crucial topic of consideration

Not only does the slag foaming practice protect the equipment covering the arcs and the refractory lining (the furnace roof and sidewalls from excessive heating and radiation), but it also reduces the arc noise, decreases electrode and electricity

generation, which is not favorable for foam stability.

Detail of one particle with considerable white ash veins.

Treatments and Recycling of Metallurgical Slags DOI: http://dx.doi.org/10.5772/intechopen.80595

3. EAF slags reused in the foaming practice

carbon content.

Figure 8.

for all steel plants.

47

Figure 7. Different types of porous carbonaceous particles identified.

Size distribution of carbonaceous particles was determined by ASTM sieves. It was observed that sample C1 has particles of small sizes, sample C2 also contains particles of up to ≈ 0.75 mm, and sample C3 presents particles between 0.80 and 2.5 mm. The morphology, the phases present, and the porosity of the carbonaceous particles were studied by light and scanning electron microscopy including EDS analysis. Different types of carbonaceous particles were identified in all the samples (Figure 7). Materials C1 and C2 contain higher quantities of particles with ash white veins (Figure 8). This result is consistent with the %Ash experimentally determined.

The morphology, size, and distribution of pores in each type of carbonaceous particles are variable. There are irregular, spherical, and elongated pores of different sizes and proportion in the particles observed. It was possible to establish that sample C3 has the largest proportion of pores with different sizes (800–50 μm), and samples C2 and C1 present porous with sizes between 350 and 50 μm. Rahman et al. [19] informed that metallurgical cokes (such as materials C1 and C2) promote gas emissions one order higher (in magnitude) than the synthetic coke. This is explained by the higher chemical interaction in contact with the slag, due to the reduction of the oxides present in the ash and FeO content. To control foam height, carbonaceous particles can be added to slag with adequate size and low volatile content. This is another alternative to avoid the risk of slopping. It is important to highlight that the foaming index decreases as the size of carbonaceous particle increases. Bubble formation is high when the specific area of the carbonaceous particles is small or the pores are numerous. On this base, material C3 is the most favorable for the slag foaming practice due to the size and distribution of the pores. Treatments and Recycling of Metallurgical Slags DOI: http://dx.doi.org/10.5772/intechopen.80595

#### Figure 8.

Size distribution of carbonaceous particles was determined by ASTM sieves. It was observed that sample C1 has particles of small sizes, sample C2 also contains particles of up to ≈ 0.75 mm, and sample C3 presents particles between 0.80 and 2.5 mm. The morphology, the phases present, and the porosity of the carbonaceous particles were studied by light and scanning electron microscopy including EDS analysis. Different types of carbonaceous particles were identified in all the samples (Figure 7). Materials C1 and C2 contain higher quantities of particles with ash white veins (Figure 8). This result is consistent with the %Ash experimentally deter-

Carbonaceous material % H2O (at 105°C) %Ash %Volatile %C %S C1 0.76 11.81 1.84 86.35 0.62 C2 1.02 10.95 1.38 87.67 0.70 C3 0.61 0.20 2.24 97.56 0.63

The morphology, size, and distribution of pores in each type of carbonaceous particles are variable. There are irregular, spherical, and elongated pores of different sizes and proportion in the particles observed. It was possible to establish that sample C3 has the largest proportion of pores with different sizes (800–50 μm), and samples C2 and C1 present porous with sizes between 350 and 50 μm. Rahman et al. [19] informed that metallurgical cokes (such as materials C1 and C2) promote gas emissions one order higher (in magnitude) than the synthetic coke. This is explained by the higher chemical interaction in contact with the slag, due to the reduction of the oxides present in the ash and FeO content. To control foam height, carbonaceous particles can be added to slag with adequate size and low volatile content. This is another alternative to avoid the risk of slopping. It is important to highlight that the foaming index decreases as the size of carbonaceous particle increases. Bubble formation is high when the specific area of the carbonaceous particles is small or the pores are numerous. On this base, material C3 is the most favorable for the slag foaming practice due to the size and distribution of the pores.

mined.

46

Figure 7.

Table 4.

Different types of porous carbonaceous particles identified.

Chemical characteristics of carbonaceous materials.

Recovery and Utilization of Metallurgical Solid Waste

Detail of one particle with considerable white ash veins.

Furthermore, the ash content of materials C1 and C2 allows predicting rapid gas generation, which is not favorable for foam stability.

Based on these results, it is possible to confirm that the evolution of properties (viscosity and surface tension) of BOF slags during the operation represents the key to obtain the best aptitude for foaming practice, avoiding the risk of slopping. High viscosity is perhaps the most obvious factor in the stabilization of BOF-converter foams, and it retards the rate of drainage in the films of the bubbles. Nevertheless, surface tension is also a relevant physical property that should be taken into account to predict foam behavior. Both properties, high viscosity and surface tension, are determined by the chemical composition and the evolution of the slag at process conditions. Carbonaceous materials also exert an effect in the foaming practice; it is possible to recommend the addition of petroleum coke (material C3) in the foaming practice, because of its ash low content, high proportion of large pores, and higher carbon content.

#### 3. EAF slags reused in the foaming practice

Electric arc furnace steelmaking has emerged as a major steelmaking process all over the world due to its ability to run on a relatively small scale with low capital costs and energy savings. Steel scrap is the preferred metallic charge material, and sponge iron is also used regularly in most plants in order to dilute tramp elements introduced through the scrap [1, 17]. The growth of the arc furnace-based steel industry has been encouraged by modern arc furnaces of large capacity and ultrahigh power, electrical efficiency improvement, and metallurgical efficiency through oxygen lancing or the co-jet technology. In conventional EAF steelmaking, natural gas is generally used as a supplementary energy source. Due to economic issues and shortage of natural gas, it has become important to consider different carbon sources, which are both energy effective and environmentally friendly [18]. In addition, the decrease of refractory consumption is a crucial topic of consideration for all steel plants.

Not only does the slag foaming practice protect the equipment covering the arcs and the refractory lining (the furnace roof and sidewalls from excessive heating and radiation), but it also reduces the arc noise, decreases electrode and electricity

consumption, and has present a significant impact on improving thermal efficiency. The foamy slag provides an insulating layer to the melt, thereby reducing energy loss. Slag foaming involves the expansion of molten slag by CO gas bubbles evolving from chemical reactions at the slag-metal interface. Slag viscosity and surface tension control the movement of bubbles in the liquid. Foaming was generally found to improve as surface tension decreases, increasing slag viscosity and suspension of second-phase particles. The reaction between FeO present in the slag and carbon is strongly endothermic. It is important to note that sulfur additions suppressed slag foaming and tended to increase the size of CO gas bubbles. An increase in silica concentration promotes lower surface tension of slag and leads to smaller CO gas bubbles and their easier escape from the slag. The injection of oxygen and carbonaceous materials in industrial EAF furnaces creates highly dynamic and nonsteady state conditions. Oxidation and reduction reactions continuously change slag composition, and chemical reactions produce CO gas that also changes significantly with time [19].

furnace slag with high-pressurized water [20]. Blast furnace slags cooled in air constitute a crystallized material used as raw material instead of sand in the production of concrete. In the case of water applied during granulated slag production, it is possible to recover heat from the slag quenching water, thereby reducing energy consumption. Blast furnace slag is obtained at 1300–1400°C; viscosity is around 0.4–1.0 poise; the chemical composition mainly includes FeO, CaO, MgO, SiO2, Al2O3, TiO2, S, and C; the alkalinity (CaO/SiO2) is 1.2; and the alkalinity [(CaO + MgO)/SiO2] is around 1.5. A lot of research has focused on the reuse of blast furnace slag to make building materials. Crystallized slag sand is added to Portland cement in particles of ≈ 3.15 mm. The chemical and mineralogical composition of Portland cement is detailed in Table 5. Senani et al. [21] informed that concrete with crystallized slag sand addition presents good physical and mechanical properties. This study confirms that the additions of blast furnace slags (0–4 mm of size) in concrete (up to 20–25%) result in good compressive strength (≈30 MPa

The use of blast furnace slag as artificial rocks is also possible because they are similar to semi-hard stones. As a recyclable material, they support resource conservation by substituting nonrenewable natural stone. Land and marine applications include seaport and airport civil engineering projects, coastal protection structures, seaweed bed rehabilitation, and land surface coverage [22]. This type of slag may represent a good alternative to reduce the cost of cement production, contribute to environment protection, and provide enormous social and economic benefits.

Brand and Roesler studied different basic steel slags: energy optimizing furnace

Chemical composition of Portland cement Range (%) Mineralogical composition Range (%) CaO 56–63 C3S 50–65 Al2O3 4–6 C2S 10–25 SiO2 19–27 C3A 9–12 Fe2O3 2.5–3.5 C4AF 7–11

(EOF), electric arc furnace (EAF), and arc oxygen decarbonization (AOD), as aggregates in concretes [23]. However, for civil applications, exhaustive controls are carried out in order to determine contents of Ba, Cd, Cr, Mo, Ni, Pb, V, and Zn, in order to avoid soil contamination. The content of sulfates or sulfides is also controlled to avoid SO2 emissions causing air pollution. It was found that steel slag is volumetrically unstable as compared to blast furnace slag due to the content of expansive oxides such as MgO and CaO. In the case of basic slags, the authors propose to modify the surface of the aggregates by blending them with a slurry mixture of fine quarry dust and cement in order to avoid the expansion and to reduce the porosity. Another possibility is the use of steel slag as a binder or filler replacement in composite materials in civil engineering production. These binder or

after 28 days) for the grades of concretes tested.

Treatments and Recycling of Metallurgical Slags DOI: http://dx.doi.org/10.5772/intechopen.80595

MgO 1–2 Na2O 0.1–0.6 K2O 0.3–0.6 Cl 0–0.2 SO3 2–3 CaO 0.5–2.5

Chemical and mineralogical composition of Portland cement.

Table 5.

49

In agreement with BOF foaming practice, the rate of gas generation was found to be an important parameter in carbon-slag interactions and needs to be optimized to maintain optimum levels/duration of gas entrapment by the slag and foaming behavior. The type of carbonaceous material added affects the foaming practice. Metallurgical cokes affect foaming because of the ash content. Natural graphite, on the other hand, produces excellent slag volumes but slow reduction of iron oxide. Slower rates of gas generation and higher surface tension values cause slag to trap gases and sustain foaming. Slag foaming height is well connected to carbon injection rate and slag chemical properties. Bubble sizes in EAF slags are ≈ 1–2 mm. In general, bubble number in the slag foam is greater than the number of coal particles. One particle of coal can form more than one bubble. In EAF steelmaking, the foam becomes less stable toward the end of the process.

#### 4. Reused of ladle slags

The amount of ladle slag generated in the steelmaking is important. The former method of recycling ladle slag is pouring the molten slag from a ladle to another or making ladle slag ingot [3]. The ingot production is complex. However, nowadays three main types of ladle slag recycle products are used depending on the particle size and chemical composition: (a) desulfurizing agent in hot metal pretreatment, (b) as a product to substitute converter flux, and (c) as a product to substitute ladle flux. It is possible to reduce steelmaking cost and get ecofriendly benefits, recycling ladle slag.

Ladle slags present similar melting behavior respect synthetic flux (Ts ffi 1334°C, Tf ffi 1346°C) and also have a good inclusion absorptivity. For this reason, they constitute an alternative for ladle flux substitution. Slag low-melting point possibilitates the application in ladles during secondary refining process reducing the fluorspar or lime additions. Finally, lumps of slags could be added in BOF to improve dephosphorization.

#### 5. Slags reused as concrete raw material

Slag is a partially vitreous byproduct of the process of smelting ore, which separates the desired metal fraction from the unwanted fraction. Blast furnace slag is furthermore classified into granulated blast furnace slag and air-cooled blast furnace slag. Granulated blast furnace slag is produced by quenching molten

Treatments and Recycling of Metallurgical Slags DOI: http://dx.doi.org/10.5772/intechopen.80595

consumption, and has present a significant impact on improving thermal efficiency. The foamy slag provides an insulating layer to the melt, thereby reducing energy loss. Slag foaming involves the expansion of molten slag by CO gas bubbles evolving from chemical reactions at the slag-metal interface. Slag viscosity and surface tension control the movement of bubbles in the liquid. Foaming was generally found to improve as surface tension decreases, increasing slag viscosity and suspension of second-phase particles. The reaction between FeO present in the slag and carbon is strongly endothermic. It is important to note that sulfur additions suppressed slag foaming and tended to increase the size of CO gas bubbles. An increase in silica concentration promotes lower surface tension of slag and leads to smaller CO gas bubbles and their easier escape from the slag. The injection of oxygen and carbonaceous materials in industrial EAF furnaces creates highly dynamic and nonsteady state conditions. Oxidation and reduction reactions continuously change slag composition, and chemical reactions produce CO gas that also changes significantly with

In agreement with BOF foaming practice, the rate of gas generation was found to be an important parameter in carbon-slag interactions and needs to be optimized to maintain optimum levels/duration of gas entrapment by the slag and foaming behavior. The type of carbonaceous material added affects the foaming practice. Metallurgical cokes affect foaming because of the ash content. Natural graphite, on the other hand, produces excellent slag volumes but slow reduction of iron oxide. Slower rates of gas generation and higher surface tension values cause slag to trap gases and sustain foaming. Slag foaming height is well connected to carbon injection rate and slag chemical properties. Bubble sizes in EAF slags are ≈ 1–2 mm. In general, bubble number in the slag foam is greater than the number of coal particles. One particle of coal can form more than one bubble. In EAF steelmaking, the foam

The amount of ladle slag generated in the steelmaking is important. The former method of recycling ladle slag is pouring the molten slag from a ladle to another or making ladle slag ingot [3]. The ingot production is complex. However, nowadays three main types of ladle slag recycle products are used depending on the particle size and chemical composition: (a) desulfurizing agent in hot metal pretreatment, (b) as a product to substitute converter flux, and (c) as a product to substitute ladle flux. It is possible to reduce steelmaking cost and get ecofriendly benefits, recycling

Ladle slags present similar melting behavior respect synthetic flux (Ts ffi 1334°C,

Tf ffi 1346°C) and also have a good inclusion absorptivity. For this reason, they constitute an alternative for ladle flux substitution. Slag low-melting point possibilitates the application in ladles during secondary refining process reducing the fluorspar or lime additions. Finally, lumps of slags could be added in BOF to

Slag is a partially vitreous byproduct of the process of smelting ore, which separates the desired metal fraction from the unwanted fraction. Blast furnace slag is furthermore classified into granulated blast furnace slag and air-cooled blast furnace slag. Granulated blast furnace slag is produced by quenching molten

becomes less stable toward the end of the process.

Recovery and Utilization of Metallurgical Solid Waste

4. Reused of ladle slags

improve dephosphorization.

5. Slags reused as concrete raw material

time [19].

ladle slag.

48

furnace slag with high-pressurized water [20]. Blast furnace slags cooled in air constitute a crystallized material used as raw material instead of sand in the production of concrete. In the case of water applied during granulated slag production, it is possible to recover heat from the slag quenching water, thereby reducing energy consumption. Blast furnace slag is obtained at 1300–1400°C; viscosity is around 0.4–1.0 poise; the chemical composition mainly includes FeO, CaO, MgO, SiO2, Al2O3, TiO2, S, and C; the alkalinity (CaO/SiO2) is 1.2; and the alkalinity [(CaO + MgO)/SiO2] is around 1.5. A lot of research has focused on the reuse of blast furnace slag to make building materials. Crystallized slag sand is added to Portland cement in particles of ≈ 3.15 mm. The chemical and mineralogical composition of Portland cement is detailed in Table 5. Senani et al. [21] informed that concrete with crystallized slag sand addition presents good physical and mechanical properties. This study confirms that the additions of blast furnace slags (0–4 mm of size) in concrete (up to 20–25%) result in good compressive strength (≈30 MPa after 28 days) for the grades of concretes tested.

The use of blast furnace slag as artificial rocks is also possible because they are similar to semi-hard stones. As a recyclable material, they support resource conservation by substituting nonrenewable natural stone. Land and marine applications include seaport and airport civil engineering projects, coastal protection structures, seaweed bed rehabilitation, and land surface coverage [22]. This type of slag may represent a good alternative to reduce the cost of cement production, contribute to environment protection, and provide enormous social and economic benefits.

Brand and Roesler studied different basic steel slags: energy optimizing furnace (EOF), electric arc furnace (EAF), and arc oxygen decarbonization (AOD), as aggregates in concretes [23]. However, for civil applications, exhaustive controls are carried out in order to determine contents of Ba, Cd, Cr, Mo, Ni, Pb, V, and Zn, in order to avoid soil contamination. The content of sulfates or sulfides is also controlled to avoid SO2 emissions causing air pollution. It was found that steel slag is volumetrically unstable as compared to blast furnace slag due to the content of expansive oxides such as MgO and CaO. In the case of basic slags, the authors propose to modify the surface of the aggregates by blending them with a slurry mixture of fine quarry dust and cement in order to avoid the expansion and to reduce the porosity. Another possibility is the use of steel slag as a binder or filler replacement in composite materials in civil engineering production. These binder or


Table 5. Chemical and mineralogical composition of Portland cement. filler substitutes were mixed into composites, and their compressive strength was tested with good results.

References

s10853-009-3046-1

EOSC; 2003. pp. 175-181

10.1.1.200.2234

and News. 2004;9:21-24. DOI:

10.10.1002/srin.19870151310

[1] Chakrabaharti AK. Steel Making. 1st ed. PHI Learning Private Limited; 2014. 230 p. ISBN: 978–81–203-3050-4

Treatments and Recycling of Metallurgical Slags DOI: http://dx.doi.org/10.5772/intechopen.80595

> [9] Cicutti C, Valdez M, Pérez T, Donayo R, Petroni J. Analysis of slag foaming during the operation of an industrial converter. Latin American Applied Research. 2001;32:237-247.

[10] Santini L, Pérez J, Rapetto A, Benavidez ER, Brandaleze E. Evaluation of BOF slag applied in foaming practice. In: AISTech Conference Proceedings (Aistech 2013); 6–9 May 2013; Pittsburgh, Pennsylvania, USA. 2013. pp. 2105-2112. ISSN: 1551-6997

[11] Pretorius EB, Carlisle RC. Foamy slag fundamentals and their practical application to electric furnace

steelmaking. In: Proceedings of the 16th Process Technology Conference; 1998 Nov 15-18; New Orleans, LA, USA. 1998. pp. 275-292. DOI: 10.1590/ 1980-5373-MR-2016-0059

[12] Ismail AN, Nur Farhana MY, Jamaludin SB, Idris MA. Influence of recycled wastes on slag foaming during EAF steelmaking. Materials Science Forum. 2015;819:381-386. ISSN:1662- 9752. DOI: 10.4028/www.scientific.net/

[13] Kapilashrami A. Interfacial phenomena in two phase systems: Emulsions and slag foaming [thesis].

Stockholm: Royal Institute of

Technology; 2004. ISBN: 91-7283-930-9

[14] Zhang GH, Chou KC, Mills KC. Modelling viscosities of CaO-MgO-Al2O3-SiO2 molten slags. ISIJ

International. 2012;52-3:633-637. DOI: 10.1016/S1006-706X (16)30099-1

[15] Mills KC. The Estimation of Slag Properties. Short Course presented in the Southern African Pyrometallurgy; 2011

[16] Matsura H, Fruehan RJ. Slag foaming in an electric arc furnace. ISIJ International. 2009;49-10:1530-1539

MSF.819.381

ISSN: 1851-8796

[2] Jung E-J, Kim W, Sohn I, Min DJ. A study on interfacial tension behaviour between solid iron-CaO-SiO2-MO system. Journal of Materials Science. 2010;45:2023-2029. DOI: 10.1007/

[3] Choi IS, Song WY, Yoon C, Shin KC. The technology of recycling ladle slag. In: Proceedings of the 4th European Oxygen Steelmaking Conference (EOSC '03); 12–15 May 2003. Graz, Austria:

[4] Madías J, Brandaleze E, Topolevsky R, Camelli S. Slag-refractory adherence mechanisms. Refractories Applications

[5] Urbain G. Viscosity of silicate melts. Transactions and Journal of the British Ceramic Society. 1981;80:139-141. DOI:

[6] Bale CW, Belisle E, Chartrand P, Degterov SA, Eriksson G, Gheribi AE, Hack K, Jung IH, Kang YB, Melançon AD, Pelton AD, Petersen S, Robelin C, Sangster J, Spencer P, Van Ende MA. FactSage thermochemical software and databases—2010–2016. CALPHAD: Computer Coupling of Phase Diagrams and Thermochemistry. 2016;54:35-53. DOI: 10.1016/j.calphad.2016.05.002

[7] Brandaleze E, Valentini M, Santini L,

[8] Seetharaman S, Teng L, Hayashi M, Wang L. Understanding the properties of slags. ISIJ International. 2013;53(1): 1-8. DOI: 10.2355/isijinternational.53.1

Benavidez E. Study on fluoride evaporation from casting powders. Journal of Thermal Analysis and Calorimetry. 2018;133(1):271-277. DOI:

10.1007/s10973-018-7227-6

51

## 6. Conclusion

The disposal and exploitation of residues from steelmaking plants are still an open problem because of the huge amount and the remarkable variety of waste materials. Slag recycling in the steel job constitutes a relevant way of reusing with important economic impact on refractory costs. The coating and foaming practices are very useful in BOF converters and EAF. The ladle slag recycling also represents an important alternative to reduce steelmaking cost, decreasing the consumption of fluorspar and lime (among others metallurgical applications), and get ecofriendly benefits.

The growing trend in the construction industry is to develop sustainable buildings. The principles underneath this movement bring new requirements with an emphasis on the rational use of material and energy resources by controlled minimization of total emissions produced. One of the possible ways of achieving sustainable development in the construction industry is to use easily renewable raw material resources and waste materials instead of limited and finite resources. In this sense, the interest shown by the professional community in aggregates based on secondary raw materials is increasing, and slags constitute a good alternative.

## Author details

Elena Brandaleze\*, Edgardo Benavidez and Leandro Santini High Temperature Physicochemistry Group, Metallurgy Department, DEYTEMA Center, Universidad Tecnológica Nacional, Facultad Regional San Nicolás, San Nicolás, Argentina

\*Address all correspondence to: ebrandaleze@frsn.utn.edu.ar

© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Treatments and Recycling of Metallurgical Slags DOI: http://dx.doi.org/10.5772/intechopen.80595

## References

filler substitutes were mixed into composites, and their compressive strength was

The disposal and exploitation of residues from steelmaking plants are still an open problem because of the huge amount and the remarkable variety of waste materials. Slag recycling in the steel job constitutes a relevant way of reusing with important economic impact on refractory costs. The coating and foaming practices are very useful in BOF converters and EAF. The ladle slag recycling also represents an important alternative to reduce steelmaking cost, decreasing the consumption of fluorspar and lime (among others metallurgical applications), and get ecofriendly

The growing trend in the construction industry is to develop sustainable buildings. The principles underneath this movement bring new requirements with an emphasis on the rational use of material and energy resources by controlled minimization of total emissions produced. One of the possible ways of achieving sustainable development in the construction industry is to use easily renewable raw material resources and waste materials instead of limited and finite resources. In this sense, the interest shown by the professional community in aggregates based on secondary raw materials is increasing, and slags constitute a good alternative.

tested with good results.

Recovery and Utilization of Metallurgical Solid Waste

6. Conclusion

benefits.

Author details

50

San Nicolás, Argentina

provided the original work is properly cited.

Elena Brandaleze\*, Edgardo Benavidez and Leandro Santini

\*Address all correspondence to: ebrandaleze@frsn.utn.edu.ar

High Temperature Physicochemistry Group, Metallurgy Department, DEYTEMA Center, Universidad Tecnológica Nacional, Facultad Regional San Nicolás,

© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

[1] Chakrabaharti AK. Steel Making. 1st ed. PHI Learning Private Limited; 2014. 230 p. ISBN: 978–81–203-3050-4

[2] Jung E-J, Kim W, Sohn I, Min DJ. A study on interfacial tension behaviour between solid iron-CaO-SiO2-MO system. Journal of Materials Science. 2010;45:2023-2029. DOI: 10.1007/ s10853-009-3046-1

[3] Choi IS, Song WY, Yoon C, Shin KC. The technology of recycling ladle slag. In: Proceedings of the 4th European Oxygen Steelmaking Conference (EOSC '03); 12–15 May 2003. Graz, Austria: EOSC; 2003. pp. 175-181

[4] Madías J, Brandaleze E, Topolevsky R, Camelli S. Slag-refractory adherence mechanisms. Refractories Applications and News. 2004;9:21-24. DOI: 10.1.1.200.2234

[5] Urbain G. Viscosity of silicate melts. Transactions and Journal of the British Ceramic Society. 1981;80:139-141. DOI: 10.10.1002/srin.19870151310

[6] Bale CW, Belisle E, Chartrand P, Degterov SA, Eriksson G, Gheribi AE, Hack K, Jung IH, Kang YB, Melançon AD, Pelton AD, Petersen S, Robelin C, Sangster J, Spencer P, Van Ende MA. FactSage thermochemical software and databases—2010–2016. CALPHAD: Computer Coupling of Phase Diagrams and Thermochemistry. 2016;54:35-53. DOI: 10.1016/j.calphad.2016.05.002

[7] Brandaleze E, Valentini M, Santini L, Benavidez E. Study on fluoride evaporation from casting powders. Journal of Thermal Analysis and Calorimetry. 2018;133(1):271-277. DOI: 10.1007/s10973-018-7227-6

[8] Seetharaman S, Teng L, Hayashi M, Wang L. Understanding the properties of slags. ISIJ International. 2013;53(1): 1-8. DOI: 10.2355/isijinternational.53.1

[9] Cicutti C, Valdez M, Pérez T, Donayo R, Petroni J. Analysis of slag foaming during the operation of an industrial converter. Latin American Applied Research. 2001;32:237-247. ISSN: 1851-8796

[10] Santini L, Pérez J, Rapetto A, Benavidez ER, Brandaleze E. Evaluation of BOF slag applied in foaming practice. In: AISTech Conference Proceedings (Aistech 2013); 6–9 May 2013; Pittsburgh, Pennsylvania, USA. 2013. pp. 2105-2112. ISSN: 1551-6997

[11] Pretorius EB, Carlisle RC. Foamy slag fundamentals and their practical application to electric furnace steelmaking. In: Proceedings of the 16th Process Technology Conference; 1998 Nov 15-18; New Orleans, LA, USA. 1998. pp. 275-292. DOI: 10.1590/ 1980-5373-MR-2016-0059

[12] Ismail AN, Nur Farhana MY, Jamaludin SB, Idris MA. Influence of recycled wastes on slag foaming during EAF steelmaking. Materials Science Forum. 2015;819:381-386. ISSN:1662- 9752. DOI: 10.4028/www.scientific.net/ MSF.819.381

[13] Kapilashrami A. Interfacial phenomena in two phase systems: Emulsions and slag foaming [thesis]. Stockholm: Royal Institute of Technology; 2004. ISBN: 91-7283-930-9

[14] Zhang GH, Chou KC, Mills KC. Modelling viscosities of CaO-MgO-Al2O3-SiO2 molten slags. ISIJ International. 2012;52-3:633-637. DOI: 10.1016/S1006-706X (16)30099-1

[15] Mills KC. The Estimation of Slag Properties. Short Course presented in the Southern African Pyrometallurgy; 2011

[16] Matsura H, Fruehan RJ. Slag foaming in an electric arc furnace. ISIJ International. 2009;49-10:1530-1539

Chapter 4

Abstract

1. Introduction

building in 2011 [4].

SiO3

53

The Comprehensive Utilization of

Steel Slag in Agricultural Soils

Lais Lorena Queiroz Moreira, Leonardo Theodoro Büll

The use of metallurgical solid wastes such as steel slag, in agricultural activity, has become very important to contribute to reducing the accumulation of such wastes in the environment and to increase crop production. So, this chapter aims to emphasize the main aspects of the application of slags to soil chemical attributes as elevation of pH and neutralization of Al3+ toxic in acid soils and increase nutrient content as phosphorus, calcium, magnesium, some micronutrients, and silicon. In addition, the advance in studies of the utilization of these residues in no-tillage systems in tropical soils will be discussed. Aspects related to monitoring the pres-

Keywords: calcium and magnesium silicate, soil fertility, steel industry residue

The metallurgical industries can produce various residues, and some of these residues can be utilized with success in the agricultural activity, as in the case of the steel slag, which has brought important contributions in agricultural production. In agriculture, slags can be used as fertilizers and corrective of soil acidity [1]. Slags are calcium and magnesium silicates, which show neutralizing action due to

<sup>2</sup> base [2]. Additionally, steel slags have been used as a low-cost source to supply Si to rice plants [3]. In China, the first steel slag fertilizer program invested by Taiyuan Iron and Steel Group and Harsco Corporation of the USA started

Steel slag is the result of industrial processes in which iron mineral is reduced, generating products as pig iron (iron with a high proportion of carbon) and steel. These processes can occur in different types of furnaces such as basic oxygen furnace or electric arc furnace [5]. Inside the furnaces, oxygen pressure is injected to remove impurities such as gaseous carbon monoxide, silicon, manganese, phosphorus, and some iron as liquid oxides; these impurities combine with lime and

Angélica Cristina Fernandes Deus,

Guilherme Constantino Meirelles,

and Dirceu Maximino Fernandes

ence of heavy metals will be addressed.

Rosemary Marques de Almeida Bertani,

Anelisa de Aquino Vidal Lacerda Soares,

[17] Zaharia M, Sahajwalla V, Khanna R, Koshy P, O'Kane P. Carbon/slag interactions between coke/rubber blends and EAF slag at 1550°C. ISIJ International. 2009;49-10:1513-1521. DOI: 10.2355/isijinternational.49.1513

[18] Pretorious EB. Slags and the Relationship with Refractory Life and Steel Production. ABM Brasil: ABM Course. Process Technology Group, LWB Refractories; 2003

[19] Rhaman M, Khanna R, Sahajwalla V, O'Kane P. The influence of ash impurities on interfacial reactions between carbonaceous materials and EAF slag at 1550°C. ISIJ International. 2009;49-3:329-336. DOI: 10.2355/ isijinternational.49.329

[20] Junak J, Stevulova N. The study of washed recycled concrete aggregates and blast furnace slag utilization in concrete production. Advanced Materials Research. 2015;1100(3): 197-201. DOI: 10.4028/www.scientific. net/AMR.1100.197

[21] Senami M, Ferhoune N, Guettala A. Substitution of the natural sand by crystallized slag of blast furnace in the composition of the concrete. Alexandria Engineering Journal. DOI: 10.1016/j. aej.2016.05.006. in press

[22] Gu HF, Yao CG. Environmental conservation efforts and byproducts recycling technologies of JFE. Advanced Materials Research. 2012;573–574: 379-382. DOI: 10.4028/www.scientific. net/AMR.573-574.379

[23] Sabapathy YK, Balasubramanian VB, Shankari NS, Kumar AY, Ravichandar D. Experimental investigation of surface modified EOF steel slags as coarse aggregate in concrete. Journal of King Saud University- Engineering Sciences. DOI: 10.1016/j.jksues.2016.07.002

## Chapter 4

[17] Zaharia M, Sahajwalla V, Khanna R,

Recovery and Utilization of Metallurgical Solid Waste

[19] Rhaman M, Khanna R, Sahajwalla V,

[20] Junak J, Stevulova N. The study of washed recycled concrete aggregates and blast furnace slag utilization in concrete production. Advanced Materials Research. 2015;1100(3): 197-201. DOI: 10.4028/www.scientific.

[21] Senami M, Ferhoune N, Guettala A. Substitution of the natural sand by crystallized slag of blast furnace in the composition of the concrete. Alexandria Engineering Journal. DOI: 10.1016/j.

[22] Gu HF, Yao CG. Environmental conservation efforts and byproducts recycling technologies of JFE. Advanced Materials Research. 2012;573–574: 379-382. DOI: 10.4028/www.scientific.

[23] Sabapathy YK, Balasubramanian VB, Shankari NS, Kumar AY, Ravichandar D. Experimental

investigation of surface modified EOF steel slags as coarse aggregate in concrete. Journal of King Saud University- Engineering Sciences. DOI: 10.1016/j.jksues.2016.07.002

Koshy P, O'Kane P. Carbon/slag interactions between coke/rubber blends and EAF slag at 1550°C. ISIJ International. 2009;49-10:1513-1521. DOI: 10.2355/isijinternational.49.1513

[18] Pretorious EB. Slags and the Relationship with Refractory Life and Steel Production. ABM Brasil: ABM Course. Process Technology Group,

O'Kane P. The influence of ash impurities on interfacial reactions between carbonaceous materials and EAF slag at 1550°C. ISIJ International. 2009;49-3:329-336. DOI: 10.2355/

LWB Refractories; 2003

isijinternational.49.329

net/AMR.1100.197

aej.2016.05.006. in press

net/AMR.573-574.379

52

## The Comprehensive Utilization of Steel Slag in Agricultural Soils

Angélica Cristina Fernandes Deus, Rosemary Marques de Almeida Bertani, Guilherme Constantino Meirelles, Anelisa de Aquino Vidal Lacerda Soares, Lais Lorena Queiroz Moreira, Leonardo Theodoro Büll and Dirceu Maximino Fernandes

### Abstract

The use of metallurgical solid wastes such as steel slag, in agricultural activity, has become very important to contribute to reducing the accumulation of such wastes in the environment and to increase crop production. So, this chapter aims to emphasize the main aspects of the application of slags to soil chemical attributes as elevation of pH and neutralization of Al3+ toxic in acid soils and increase nutrient content as phosphorus, calcium, magnesium, some micronutrients, and silicon. In addition, the advance in studies of the utilization of these residues in no-tillage systems in tropical soils will be discussed. Aspects related to monitoring the presence of heavy metals will be addressed.

Keywords: calcium and magnesium silicate, soil fertility, steel industry residue

## 1. Introduction

The metallurgical industries can produce various residues, and some of these residues can be utilized with success in the agricultural activity, as in the case of the steel slag, which has brought important contributions in agricultural production.

In agriculture, slags can be used as fertilizers and corrective of soil acidity [1]. Slags are calcium and magnesium silicates, which show neutralizing action due to SiO3 <sup>2</sup> base [2]. Additionally, steel slags have been used as a low-cost source to supply Si to rice plants [3]. In China, the first steel slag fertilizer program invested by Taiyuan Iron and Steel Group and Harsco Corporation of the USA started building in 2011 [4].

Steel slag is the result of industrial processes in which iron mineral is reduced, generating products as pig iron (iron with a high proportion of carbon) and steel. These processes can occur in different types of furnaces such as basic oxygen furnace or electric arc furnace [5]. Inside the furnaces, oxygen pressure is injected to remove impurities such as gaseous carbon monoxide, silicon, manganese, phosphorus, and some iron as liquid oxides; these impurities combine with lime and

dolomitic lime to form the steel slag. Steel can also undergo a greater process of refinement, into a ladle and, at the end of the process, to generate ladle steel slag [5]. The steel slags from these two furnaces are very similar. However, ladle steel slag, resulting from further refining, is quite different from steel slag [5]. For production of every tone of steel, nearly 150 kg of slag is generated [6].

There are several types of steel slag, which present variation in chemical composition, physical composition, and solubility, and these variations occur mainly, due to the different processes and different raw materials used in the metallurgical industries. Examples of slags are steel slag, stainless steel slag, ladle furnace slag, and blast furnace slag; all of these residues have already been tested for agricultural use at some moment, as will be shown in the chapter.

#### 2. Steel slag composition

The main chemical components, which slags contain in their composition and which are important for their use in agriculture, are CaO, MgO, SiO2, P2O5, FeO, and MnO. The amount of these components in each slag varies widely depending on raw materials, type of steel made, furnace conditions, and other aspects [4, 5].

the blast furnace slag with higher content of manganese; the presence of higher micronutrients could be interesting to provide this element for the plant.

SSS, stainless steel slag; SS, steel slag; LS, ladle slag; BFS, blast furnace slag; W, wollastonite.

Materials Cu Fe Mn Zn Cd Ni Pb Cr Hg

SSS 20 38.000 5.300 50 3.1 53.6 12.6 990 <0.1 SS 30 193.500 21.500 70 14.5 3.0 <0.5 941 <0.1 BFS 20 17.400 51.000 50 1.8 1.4 <0.5 104 <0.1 LS 20 28.600 3.700 50 1.6 1.1 <0.5 126 <0.1 W 10 600 100 40 <0.03 0.3 <0.5 0.5 <0.1

tolerable for application to the soil [10].

Micronutrients and heavy metal contents in different slags.

mg kg�<sup>1</sup>

DOI: http://dx.doi.org/10.5772/intechopen.81440

The Comprehensive Utilization of Steel Slag in Agricultural Soils

Adapted from [7].

Table 2.

greater crop production.

SiO<sup>2</sup>�

HSiO�

below [2]:

55

3. Steel slag modifying soil chemical attributes

in the soil are also important aspects to be considered.

these materials have in their composition the neutralizing base SiO3

<sup>3</sup> þ H2O soil ð Þ\$ HSiO�

The value of the ionization constant (Kb1) shows that SiO3

reacts in water and releases hydroxyl (OH�) ions, according to the equations

CaSiO3 <sup>þ</sup> H2O ! Ca<sup>2</sup><sup>þ</sup> <sup>þ</sup> SiO<sup>2</sup>�

MgSiO3 <sup>þ</sup> H2O ! Mg<sup>2</sup><sup>þ</sup> <sup>þ</sup> SiO<sup>2</sup>�

is, the OH� forming reaction is relatively slow and partial. The hydroxyl (OH�) produced neutralizes the H+ of the soil solution and the phytotoxic Al3+, and,

<sup>3</sup> <sup>þ</sup> <sup>H</sup>2<sup>O</sup> ð Þ\$ soil <sup>H</sup>2SiO<sup>3</sup> <sup>þ</sup> OH� Kb2 <sup>¼</sup> <sup>3</sup>:1 x 10�<sup>5</sup> (4)

OH� þ H<sup>þ</sup> ð Þ Soil Solution ! H2O (5) OH� <sup>þ</sup> Al<sup>3</sup><sup>þ</sup> ð Þ Soil Solution ! Al OH ð Þ<sup>3</sup> (6)

The main restriction for the use of slags is the presence of heavy metals in its composition, which have to be evaluated before their soil application. Heavy metal contents in the slags shown in Table 1 agree with the values which are considered

The results of the researchers with the use of steel slag in agriculture have demonstrated that the proper application of these residues brings benefits on the chemical attributes of the soil, such as increase of pH in acidic soils; increase in the nutrient content of phosphorus, calcium, and magnesium; and increase in the content of the beneficial element silicon [6, 11–14]; these aspects contribute to

For proper application, the initial chemical characterization of the soil to calculate the dose either for use as corrective of soil acidity or fertilizers is important. The homogeneous application of the residue in the area and the adequate incorporation

The application of slag can neutralize part of the soil acidity; this occurs because

<sup>2</sup>� [15] that

<sup>3</sup> (1)

<sup>3</sup> (2)

<sup>2</sup>� is a weak base, that

<sup>3</sup> <sup>þ</sup> OH� Kb1 <sup>¼</sup> <sup>1</sup>:6 x 10�<sup>3</sup> (3)

Table 1 shows the chemical composition of different steel slags compared to wollastonite which is a rock and is considered as the standard of silicates [7]. The chemical evaluation of soil acidity correctives for agricultural purposes consists of the following determinations: neutralization power (NP) and calcium and magnesium contents [8]. The different slags have different contents about the components that characterize a material as soil acidity corrective that can provide different effects in the neutralization of the soil acidity.

Considering the Brazilian legislation of soil acidity corrective materials [9], for example, all the slags evaluated in Table 1 can be considered as an alternative source to limestone, because the values of NP and somatory (%) of CaO and MgO are according to the established values of 60% ECaCO3 and 30%, respectively; this means that the application of such materials allows good performance in the neutralization of soil acidity.

We can also observe different concentrations of Si and P2O5 in the different slags. LS showed the highest content of Si, while SS has a great amount of P2O5 (Table 1). These variations may lead to possible increase in the content of these elements in the soil and increase in the availability to the plants.

Table 2 indicates the micronutrients and heavy metal contents in different slags [7]. It is noted that some materials have a higher amount of micronutrients, for example, the steel slag with a higher presence of iron than the other materials and


Adapted from [7].

SSS, stainless steel slag; SS, steel slag; LS, ladle slag; W, wollastonite; NP, neutralization power; RR, reactivity rate, expresses the percentage of corrective material that reacts in 3 months; ECC, effective calcium carbonate.

#### Table 1.

Chemical and physical characterization of different slags.


SSS, stainless steel slag; SS, steel slag; LS, ladle slag; BFS, blast furnace slag; W, wollastonite.

Table 2.

dolomitic lime to form the steel slag. Steel can also undergo a greater process of refinement, into a ladle and, at the end of the process, to generate ladle steel slag [5]. The steel slags from these two furnaces are very similar. However, ladle steel slag, resulting from further refining, is quite different from steel slag [5]. For production of every tone of steel, nearly 150 kg of slag is generated [6].

There are several types of steel slag, which present variation in chemical composition, physical composition, and solubility, and these variations occur mainly, due to the different processes and different raw materials used in the metallurgical industries. Examples of slags are steel slag, stainless steel slag, ladle furnace slag, and blast furnace slag; all of these residues have already been tested for agricultural

The main chemical components, which slags contain in their composition and which are important for their use in agriculture, are CaO, MgO, SiO2, P2O5, FeO, and MnO. The amount of these components in each slag varies widely depending on raw materials, type of steel made, furnace conditions, and other aspects [4, 5]. Table 1 shows the chemical composition of different steel slags compared to wollastonite which is a rock and is considered as the standard of silicates [7]. The chemical evaluation of soil acidity correctives for agricultural purposes consists of the following determinations: neutralization power (NP) and calcium and magnesium contents [8]. The different slags have different contents about the components that characterize a material as soil acidity corrective that can provide different

Considering the Brazilian legislation of soil acidity corrective materials [9], for example, all the slags evaluated in Table 1 can be considered as an alternative source to limestone, because the values of NP and somatory (%) of CaO and MgO are according to the established values of 60% ECaCO3 and 30%, respectively; this means that the application of such materials allows good performance in the neu-

We can also observe different concentrations of Si and P2O5 in the different slags. LS showed the highest content of Si, while SS has a great amount of P2O5 (Table 1). These variations may lead to possible increase in the content of these

Table 2 indicates the micronutrients and heavy metal contents in different slags [7]. It is noted that some materials have a higher amount of micronutrients, for example, the steel slag with a higher presence of iron than the other materials and

% %ECaCO3 % g kg<sup>1</sup>

Materials CaO MgO NP RR ECC Si P2O5 K2O

SSS 37.65 9.55 84 71 60 13.6 3.5 0.3 SS 28.13 6.10 70 71 50 14.2 11 0.3 LS 36.10 5.76 77 80 62 21.6 2.5 0.3 W 30.00 3.00 60 100 60 16.0 1.5 0.1

SSS, stainless steel slag; SS, steel slag; LS, ladle slag; W, wollastonite; NP, neutralization power; RR, reactivity rate, expresses the percentage of corrective material that reacts in 3 months; ECC, effective calcium carbonate.

elements in the soil and increase in the availability to the plants.

use at some moment, as will be shown in the chapter.

Recovery and Utilization of Metallurgical Solid Waste

effects in the neutralization of the soil acidity.

Chemical and physical characterization of different slags.

2. Steel slag composition

tralization of soil acidity.

Adapted from [7].

Table 1.

54

Micronutrients and heavy metal contents in different slags.

the blast furnace slag with higher content of manganese; the presence of higher micronutrients could be interesting to provide this element for the plant.

The main restriction for the use of slags is the presence of heavy metals in its composition, which have to be evaluated before their soil application. Heavy metal contents in the slags shown in Table 1 agree with the values which are considered tolerable for application to the soil [10].

#### 3. Steel slag modifying soil chemical attributes

The results of the researchers with the use of steel slag in agriculture have demonstrated that the proper application of these residues brings benefits on the chemical attributes of the soil, such as increase of pH in acidic soils; increase in the nutrient content of phosphorus, calcium, and magnesium; and increase in the content of the beneficial element silicon [6, 11–14]; these aspects contribute to greater crop production.

For proper application, the initial chemical characterization of the soil to calculate the dose either for use as corrective of soil acidity or fertilizers is important. The homogeneous application of the residue in the area and the adequate incorporation in the soil are also important aspects to be considered.

The application of slag can neutralize part of the soil acidity; this occurs because these materials have in their composition the neutralizing base SiO3 <sup>2</sup>� [15] that reacts in water and releases hydroxyl (OH�) ions, according to the equations below [2]:

$$\text{CaSiO}\_3 + \text{H}\_2\text{O} \rightarrow \text{Ca}^{2+} + \text{SiO}\_3^{2-} \tag{1}$$

$$\rm MgSiO\_3 + H\_2O \to Mg^{2+} + SiO\_3^{2-} \tag{2}$$

$$\mathrm{SiO\_3^{2-}} + \mathrm{H\_2O} \text{ (soil)} \leftrightarrow \mathrm{HSiO\_3^-} + \mathrm{OH^-} \text{ (Kb}\_1 = \text{1.6 x } \mathrm{10}^{-3}\text{)}\tag{3}$$

$$\mathrm{HSiO\_3^-} + H\_2O \text{ (soil)} \leftrightarrow H\_2SiO\_3 + OH^- \text{ (Kb}\_2 = \textbf{3.1} \ge \textbf{10}^{-5}\text{)}\tag{4}$$

$$\text{OH}^- + \text{H}^+ \text{ (Solid Solution)} \rightarrow \text{H}\_2\text{O} \tag{5}$$

$$\text{OH}^- + \text{Al}^{3+} \text{ (Soil Solution)} \rightarrow \text{Al(OH)}\_3 \tag{6}$$

The value of the ionization constant (Kb1) shows that SiO3 <sup>2</sup>� is a weak base, that is, the OH� forming reaction is relatively slow and partial. The hydroxyl (OH�) produced neutralizes the H+ of the soil solution and the phytotoxic Al3+, and,

consequently, there is an increase in pH and a decrease in the concentration of the potential acidity (H + Al) [16].

reduction of Al3+ up to 0.40 m with application of steel slag; in the same period, the

In a long-term experiment under no-tillage system, [26] applied limestone and slag to increase base saturation to 70% and observed that the steel slag corrected acidity and increased the bases up to 0.10 m at 12 months. After 18 months of reaction, the steel slag corrected the soil acidity up to 0.60 m and increased the bases up to 0.40 m, while the effects of the lime were observed until 0.20 m [28]. On the other hand, the study conducted by [7] with surface application of steel slag, blast furnace slag, ladle furnace slag, and stainless steel slag at the installation of the no-tillage system presented that the ladle furnace slag, stainless steel slag, and steel slag had similar efficiency to the lime in the neutralization of soil acidity at 24 months after application. The divergence of the results reported above with the application of slag in no-tillage system can be explained by the chemical composition of these residues, because the industrial process promotes the production of several types of slag, with different recrystallization depending on the amount of Ca

effects of limestone on the soil were observed up to 0.20 m (Figure 1) [22].

The Comprehensive Utilization of Steel Slag in Agricultural Soils

DOI: http://dx.doi.org/10.5772/intechopen.81440

and Mg and of the cooling time, aspects that may reduce its solubility [29]. In addition to the corrective effect of the slag, several studies point to the efficiency of slag to increase phosphorus nutrient in the soil [7, 17, 19]. Some researchers attribute the P content increase with the use of slag due to the competition between Si and P that occurs through the same adsorption sites of soil col-

loids. This occurs due to the application of slag (silicates) to generate a

to the colloids of Fe and Al oxides from the soil, which under the conditions of the tropical soils are in great quantity [30]. Others relate the P content increase with the increase of the soil pH provided by these materials, as well as greater solubilization of the organic phosphorus and the labile fraction, increasing its content in the form available to the plants. In addition, steel slag has P in its composition, which may

The application of steel slag in soil can contribute to the chemical attributes of the soil, reflecting the benefits to the agricultural sector; however, this contribution is variable depending on the composition of the used residue making it always important to know the chemical and physical characterization of the residue before

The presence of heavy metals in steel slag is one of the problems with its use that at high levels, it can become toxic and limit its use in agricultural activities. The steel residues have very variable chemical composition due to the different processes to obtain them, becoming the important quantification of these elements in

After 18 months of steel slag incubation in an Argisol, it is observed [31] that the

solubility of Zn, Mn, Pb, Ni, Cd, and Cu decreased due to the passage of the exchangeable form retained in oxides and residues, explained by the phenomenon of chemosorption influenced by the soil pH. In another study [33], it is found that the application of 8 and 4 Mg ha<sup>1</sup> of steel slag, respectively, did not increase the availability of heavy metals of the soil. The increase of heavy metals, such as cadmium (Cd), chromium (Cr), nickel (Ni), mercury (Hg), lead (Pb), and arsenic (As), was insignificant compared to the application of 8 t/ha [32]. The steel slag, ladle slag, and stainless steel slag (chemical characterization in Tables 1 and 2) applied as soil acidity correctives, at the dose necessary to raise the initial soil saturation to 70%, did not change the soil metals content evaluated at 12 and 23 months after the application of residues, and the Pb content decreased with the application of residues [7]. Also, the additions of heavy metals were not observed in the plant tissue of beans, soybean, and black oats cultivated in the area where the slags were applied [7, 32]. The presence of elements in the composition of residues

<sup>2</sup>), which removes the P adsorbed

concentration gradient of the anion silicate (SiO3

contribute to such results, as can be seen in Table 1.

the soil and the crops after long-term residue application.

its application to the soil.

57

Correction of acidity with slag occurs similarly to the use of limestone. In addition to the decrease in acidity levels, Ca and Mg supply also occurs in soil [6, 11, 12], with positive effects for crops such as potatoes, rice, black oats, beans, soybeans, alfalfa, coffee, and sugarcane, among others, making steel slag a source capable of being used instead of limestone [11, 13, 17–21, 23].

The application of steel slag was also studied in acidic tropical soils cultivated under no-tillage system. Tropical soils are characterized by being acid with excess of Al3+ that is a toxic element to plants because it limits the root development.

The no-tillage system is growing in these areas; however, one of the requirements for the success of this system is that there is no soil revolving, so the acidity corrective material should be applied to the surface without incorporation. Due to the fact that the limes present low solubility in water and little movement in the soil profile [24], the study of the use of slags (silicates) in no-tillage system has increased due to the greater solubility of this residue [2]. Calcium silicate is 6.78 times more soluble than lime [2], so the use of steel slag in the no-tillage system can be an important alternative source for the process of soil acidity correction, because it may promote greater mobility of SiO3 <sup>2</sup> anions in soil profile, ensuring faster soil acidity correction in deeper layers in relation to the lime.

Studies conducted by [19, 22, 25–28] showed positive effects in soil acidity correction of surface application of steel slag compared to lime in no-tillage system, in tropical soil.

After 27 months of application of steel slag at doses 2, 4, and 8 t/ha, without incorporation, under no-tillage system, there was an increase in base saturation and

#### Figure 1.

pH, base saturation (V%), and Al3+ content at different depths of a dystrophic Red Latosol at 27 months after surface application of lime, centrifuged sewage sludge (LC), steel slag, and lama cal (Lcal) in the no-tillage system (source: [22]).

#### The Comprehensive Utilization of Steel Slag in Agricultural Soils DOI: http://dx.doi.org/10.5772/intechopen.81440

consequently, there is an increase in pH and a decrease in the concentration of the

The application of steel slag was also studied in acidic tropical soils cultivated under no-tillage system. Tropical soils are characterized by being acid with excess of

The no-tillage system is growing in these areas; however, one of the requirements for the success of this system is that there is no soil revolving, so the acidity corrective material should be applied to the surface without incorporation. Due to the fact that the limes present low solubility in water and little movement in the soil

<sup>2</sup> anions in soil profile, ensuring faster soil

Al3+ that is a toxic element to plants because it limits the root development.

profile [24], the study of the use of slags (silicates) in no-tillage system has increased due to the greater solubility of this residue [2]. Calcium silicate is 6.78 times more soluble than lime [2], so the use of steel slag in the no-tillage system can be an important alternative source for the process of soil acidity correction, because

Studies conducted by [19, 22, 25–28] showed positive effects in soil acidity correction of surface application of steel slag compared to lime in no-tillage system,

After 27 months of application of steel slag at doses 2, 4, and 8 t/ha, without incorporation, under no-tillage system, there was an increase in base saturation and

pH, base saturation (V%), and Al3+ content at different depths of a dystrophic Red Latosol at 27 months after surface application of lime, centrifuged sewage sludge (LC), steel slag, and lama cal (Lcal) in the no-tillage

Correction of acidity with slag occurs similarly to the use of limestone. In addition to the decrease in acidity levels, Ca and Mg supply also occurs in soil [6, 11, 12], with positive effects for crops such as potatoes, rice, black oats, beans, soybeans, alfalfa, coffee, and sugarcane, among others, making steel slag a source

capable of being used instead of limestone [11, 13, 17–21, 23].

potential acidity (H + Al) [16].

Recovery and Utilization of Metallurgical Solid Waste

it may promote greater mobility of SiO3

in tropical soil.

Figure 1.

56

system (source: [22]).

acidity correction in deeper layers in relation to the lime.

reduction of Al3+ up to 0.40 m with application of steel slag; in the same period, the effects of limestone on the soil were observed up to 0.20 m (Figure 1) [22].

In a long-term experiment under no-tillage system, [26] applied limestone and slag to increase base saturation to 70% and observed that the steel slag corrected acidity and increased the bases up to 0.10 m at 12 months. After 18 months of reaction, the steel slag corrected the soil acidity up to 0.60 m and increased the bases up to 0.40 m, while the effects of the lime were observed until 0.20 m [28].

On the other hand, the study conducted by [7] with surface application of steel slag, blast furnace slag, ladle furnace slag, and stainless steel slag at the installation of the no-tillage system presented that the ladle furnace slag, stainless steel slag, and steel slag had similar efficiency to the lime in the neutralization of soil acidity at 24 months after application. The divergence of the results reported above with the application of slag in no-tillage system can be explained by the chemical composition of these residues, because the industrial process promotes the production of several types of slag, with different recrystallization depending on the amount of Ca and Mg and of the cooling time, aspects that may reduce its solubility [29].

In addition to the corrective effect of the slag, several studies point to the efficiency of slag to increase phosphorus nutrient in the soil [7, 17, 19]. Some researchers attribute the P content increase with the use of slag due to the competition between Si and P that occurs through the same adsorption sites of soil colloids. This occurs due to the application of slag (silicates) to generate a concentration gradient of the anion silicate (SiO3 <sup>2</sup>), which removes the P adsorbed to the colloids of Fe and Al oxides from the soil, which under the conditions of the tropical soils are in great quantity [30]. Others relate the P content increase with the increase of the soil pH provided by these materials, as well as greater solubilization of the organic phosphorus and the labile fraction, increasing its content in the form available to the plants. In addition, steel slag has P in its composition, which may contribute to such results, as can be seen in Table 1.

The application of steel slag in soil can contribute to the chemical attributes of the soil, reflecting the benefits to the agricultural sector; however, this contribution is variable depending on the composition of the used residue making it always important to know the chemical and physical characterization of the residue before its application to the soil.

The presence of heavy metals in steel slag is one of the problems with its use that at high levels, it can become toxic and limit its use in agricultural activities. The steel residues have very variable chemical composition due to the different processes to obtain them, becoming the important quantification of these elements in the soil and the crops after long-term residue application.

After 18 months of steel slag incubation in an Argisol, it is observed [31] that the solubility of Zn, Mn, Pb, Ni, Cd, and Cu decreased due to the passage of the exchangeable form retained in oxides and residues, explained by the phenomenon of chemosorption influenced by the soil pH. In another study [33], it is found that the application of 8 and 4 Mg ha<sup>1</sup> of steel slag, respectively, did not increase the availability of heavy metals of the soil. The increase of heavy metals, such as cadmium (Cd), chromium (Cr), nickel (Ni), mercury (Hg), lead (Pb), and arsenic (As), was insignificant compared to the application of 8 t/ha [32]. The steel slag, ladle slag, and stainless steel slag (chemical characterization in Tables 1 and 2) applied as soil acidity correctives, at the dose necessary to raise the initial soil saturation to 70%, did not change the soil metals content evaluated at 12 and 23 months after the application of residues, and the Pb content decreased with the application of residues [7]. Also, the additions of heavy metals were not observed in the plant tissue of beans, soybean, and black oats cultivated in the area where the slags were applied [7, 32]. The presence of elements in the composition of residues

in nontoxic amounts and the soil pH increase contributed to avoid toxicity by heavy metals [32].

to correct soil acidity, as it contains some nutrients for the plants and also as silicate fertilizer that is capable of providing silicon to the plants. Thus, steel slags can be

\*, Rosemary Marques de Almeida Bertani2

, Anelisa de Aquino Vidal Lacerda Soares<sup>3</sup>

, Leonardo Theodoro Büll<sup>1</sup> and

1 Department of Soil and Environmental Resources, College of Agronomic Sciences,

3 Paulista Agency Agribusiness Technology, Regional Pole Midwest, UPD, Marilia,

4 Federal Institute of Techonology North of Minas Gerais, Januária, Minas Gerais,

© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

2 Paulista Agency Agribusiness Technology Regional Midwest Pole, Bauru,

,

,

considered as a sustainable alternative to agricultural practice.

The Comprehensive Utilization of Steel Slag in Agricultural Soils

DOI: http://dx.doi.org/10.5772/intechopen.81440

There are no conflicts of interest to declare.

Conflict of interest

Author details

São Paulo, Brazil

São Paulo, Brazil

Brazil

59

Angélica Cristina Fernandes Deus1

Guilherme Constantino Meirelles<sup>1</sup>

São Paulo State University, Botucatu, São Paulo, Brazil

\*Address all correspondence to: angeldeys@hotmail.com

provided the original work is properly cited.

Lais Lorena Queiroz Moreira<sup>4</sup>

Dirceu Maximino Fernandes<sup>1</sup>

In the soil, heavy metals can be adsorbed by specific reactions (chemosorption) influenced by soil pH or nonspecific [33]. The pH and CEC and the presence of cations affect the adsorption and ionic speciation of heavy metals in soils [34]. In weathered soils, such as those of the cited studies, the presence of colloids with pHdependent charges represents more than 70% of the total cation binding sites. Thus, in this soil type, the acidity correction is of great importance in the adsorption of heavy metals [33].

Although the above studies did not observe an increase in the heavy metals' levels in soil and plants, monitoring of the availability of these toxic elements in the soil and in the plant, as well as the characterization of the residue to be used, is fundamental for the success in the residues used in agriculture.

#### 4. Benefits of using steel slag for crops

Slag application favors the increase of pH and the availability of nutrients such as Ca, Mg, and Si in the soil, which leads to the increase in the absorption of these elements by the plant, favoring the growth and yield of the crops. Slags application may supply silicon which is considered a beneficial element to plants. Silicon may bring benefits to plants such as reduction of foliar diseases; improvement in pest control; increase in photosynthetic capacity due to the silicon benefit to the architectural activity of the plant, leaving the leaves more upright [32]; and improvement in the use of water by the plant [35]. Si may also influence the uptake and translocation of various macro- and micronutrients and increase plant tolerance to excess of Mn and Fe [37] and Zn, Al, and Cd [38].

Slag-based fertilizers applied in Si-deficient paddy soil improved rice growth, productivity, and brown spot resistance [39]. The application of steel slag in the soil increases the concentration of Si in the rice straw and promotes a higher yield of grains [40]. Also, studying the effect of slag in rice crop, [41] observed an increase of base saturation and availability of silicon and phosphorus in the soil, with a consequent increase in grain yield, Si content, and accumulation in rice straw, in 2 years of cultivation.

The supply of P and Si available in the soil for the potato crop, through the application of slag, increased the absorption of these nutrients by the plant, decreasing the lodging and increasing the height of plants and the production of tubers [17].

Nitrogen fertilization associated with steel slag also increases the dry mass production and the absorption of Si by the marandu grass [42].

Steel slag, used as soil acidity corrective material, increased the contents of Ca, Mg, P, and Si in the soybean leaves and Ca, Mg, and Si in maize and also provided increased shoot dry matter yield and grain yield of both cultures under no-tillage system; compared to limestone, steel slag was more effective in improving maize grain yield [27].

#### 5. Conclusions

The steel industry generates large volumes of slag, which are considered as an environmental problem; it is necessary to increase the use of this waste in new processes to avoid disposal in landfills. Steel slags can be used in several activities, such as construction and paving, and also in the agricultural sector due to its ability to correct soil acidity, as it contains some nutrients for the plants and also as silicate fertilizer that is capable of providing silicon to the plants. Thus, steel slags can be considered as a sustainable alternative to agricultural practice.

## Conflict of interest

in nontoxic amounts and the soil pH increase contributed to avoid toxicity by heavy

Although the above studies did not observe an increase in the heavy metals' levels in soil and plants, monitoring of the availability of these toxic elements in the soil and in the plant, as well as the characterization of the residue to be used, is

Slag application favors the increase of pH and the availability of nutrients such as Ca, Mg, and Si in the soil, which leads to the increase in the absorption of these elements by the plant, favoring the growth and yield of the crops. Slags application may supply silicon which is considered a beneficial element to plants. Silicon may bring benefits to plants such as reduction of foliar diseases; improvement in pest control; increase in photosynthetic capacity due to the silicon benefit to the architectural activity of the plant, leaving the leaves more upright [32]; and improvement in the use of water by the plant [35]. Si may also influence the uptake and translocation of various macro- and micronutrients and increase plant tolerance to

Slag-based fertilizers applied in Si-deficient paddy soil improved rice growth, productivity, and brown spot resistance [39]. The application of steel slag in the soil increases the concentration of Si in the rice straw and promotes a higher yield of grains [40]. Also, studying the effect of slag in rice crop, [41] observed an increase of base saturation and availability of silicon and phosphorus in the soil, with a consequent increase in grain yield, Si content, and accumulation in rice straw, in

The supply of P and Si available in the soil for the potato crop, through the application of slag, increased the absorption of these nutrients by the plant, decreasing the lodging and increasing the height of plants and the production of

Nitrogen fertilization associated with steel slag also increases the dry mass pro-

Steel slag, used as soil acidity corrective material, increased the contents of Ca, Mg, P, and Si in the soybean leaves and Ca, Mg, and Si in maize and also provided increased shoot dry matter yield and grain yield of both cultures under no-tillage system; compared to limestone, steel slag was more effective in improving maize

The steel industry generates large volumes of slag, which are considered as an environmental problem; it is necessary to increase the use of this waste in new processes to avoid disposal in landfills. Steel slags can be used in several activities, such as construction and paving, and also in the agricultural sector due to its ability

fundamental for the success in the residues used in agriculture.

4. Benefits of using steel slag for crops

Recovery and Utilization of Metallurgical Solid Waste

excess of Mn and Fe [37] and Zn, Al, and Cd [38].

duction and the absorption of Si by the marandu grass [42].

In the soil, heavy metals can be adsorbed by specific reactions (chemosorption) influenced by soil pH or nonspecific [33]. The pH and CEC and the presence of cations affect the adsorption and ionic speciation of heavy metals in soils [34]. In weathered soils, such as those of the cited studies, the presence of colloids with pHdependent charges represents more than 70% of the total cation binding sites. Thus, in this soil type, the acidity correction is of great importance in the adsorption of

metals [32].

heavy metals [33].

2 years of cultivation.

tubers [17].

grain yield [27].

5. Conclusions

58

There are no conflicts of interest to declare.

## Author details

Angélica Cristina Fernandes Deus1 \*, Rosemary Marques de Almeida Bertani2 , Guilherme Constantino Meirelles<sup>1</sup> , Anelisa de Aquino Vidal Lacerda Soares<sup>3</sup> , Lais Lorena Queiroz Moreira<sup>4</sup> , Leonardo Theodoro Büll<sup>1</sup> and Dirceu Maximino Fernandes<sup>1</sup>

1 Department of Soil and Environmental Resources, College of Agronomic Sciences, São Paulo State University, Botucatu, São Paulo, Brazil

2 Paulista Agency Agribusiness Technology Regional Midwest Pole, Bauru, São Paulo, Brazil

3 Paulista Agency Agribusiness Technology, Regional Pole Midwest, UPD, Marilia, São Paulo, Brazil

4 Federal Institute of Techonology North of Minas Gerais, Januária, Minas Gerais, Brazil

\*Address all correspondence to: angeldeys@hotmail.com

© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

## References

[1] Das B, Prakash S, Reddy PSR, Misra VN. An overview of utilization of slag and sludge from steel industries. Resources, Conservation and Recycling. 2007;50:40-57. DOI: 10.1016/j. resconrec.2006.05.008

[2] Alcarde JA, Rodella AA. Qualidade e legislação de fertilizantes e corretivos. In: Curi N, Marques JJ, Guilherme LRG, Lima JM, Lopes AS, Alvares VVH, editors. Tópicos em Ciência do Solo. Sociedade Brasileira de Ciência do Solo; 2003. pp. 291-334

[3] Babu T, Tubana B, Paye W, Kanke Y, Datnoff L. Establishing soil silicon test procedure and critical silicon level for rice in Louisiana soils. Communications in Soil Science and Plant Analysis. 2016: 1532-2416

[4] Yi H, Xu G, Cheng H, Wang J, Wan Y, Chen H. An overview of utilization of steel slag. Procedia Environmental Sciences. 2012;16:791-801. DOI: 10.1016/j.proenv.2012.10.108

[5] Shi C. Steel slag its production, processing, characteristics, and cementitious properties. Journal of Materials in Civil Engineering. 2004;16: 230-236. DOI: 10.1002/chin.200522249

[6] Torkashvand AM, Sedaghathoor S. Converter slag as a liming agent in the amelioration of acidic soils. International Journal of Agriculture and Biology. 2007;9:715-720

[7] Deus ACF. Aplicação de corretivos de acidez do solo na implantação do sistema plantio direto [thesis]. Botucatu: Faculdade de Ciências Agronômicas de Botucatu—Universidade Estadual Paulista Júlio de Mesquita Filho; 2014

[8] Alcarde JC, Rodella AA. Avaliação química de corretivos de acidez para fins agrícolas: uma nova proposição. Scientia Agricola. 1996;53:211-216. DOI: 10.1590/ S0103-90161996000200003

[14] Nolla A, Korndörfer GH, Silva CAT, Silva TRB, Zucarelli V, Silva MAG. Correcting soil acidity with the use of slags. African Journal of Agricultural Research. 2013;8:5174-5180. DOI:

DOI: http://dx.doi.org/10.5772/intechopen.81440

The Comprehensive Utilization of Steel Slag in Agricultural Soils

feijoeiro em sistema de semeadura direta. Ciência Rural. 2013;43:1783-1789

[22] Correa JC, Freitag EE, Büll LT, Crusciol CAC, Fernandes DM, Marcelino R. Aplicação superficial de calcário e diferentes resíduos em soja

direto. Bragantia. 2009;68:1059-1068. DOI: 10.1590/S0006-87052009000

[23] Brassioli FB, Prado RM, Fernandes FM. Avaliação agronômica da escória de siderurgia na cana-de-açúcar durante cinco ciclos de produção. Bragantia.

[24] Flower KC, Crabtree WL. Soil pH change after surface application of lime related to the levels of soil disturbance caused by no-tillage seeding machinery. Field Crops Research. 2011;121:75-87. DOI: 10.1016/j.fcr.2010.11.014

[25] Corrêa JC, Büll LT, Crusciol CAC, Marcelino R, Mauad M. Correção da acidez e mobilidade de íons em Latossolo com aplicação superficial de escória, lama cal, lodos de esgoto e calcário. Pesquisa Agropecuária Brasileira. 2007;42:1307-1317

[26] Castro GSA, Crusciol CAC. Effects of superficial liming and silicate application on soil fertility and crop yield under rotation. Geoderma. 2013;

[27] Castro GSA, Crusciol CAC. Yield and mineral nutrition of soybean, maize, and Congo signal grass as affected by limestone and slag. Pesquisa Agropecuária Brasileira. 2013;48:

[28] Castro GSA, Crusciol CAC, Costa CHM, Ferrari Neto J, Mancuso MAC. Surface application of limestone and calcium-magnesium silicate in a tropical no-tillage system. Journal of Soil Science and Plant Nutrition. 2016;16:362-379.

cultivada no sistema plantio

400027

2009;68:381-387

195–196:234-242

673-681. DOI: 10.1590/ S0100-204X2013000600013

[15] Alcarde JC. Corretivos da acidez do solo: Características e interpretações técnicas. São Paulo—SP: Associação nacional para difusão de adubos e corretivos (ANDA); 1992. 62 p. Boletim

[16] Prado RM, Fernandes FM, Natale W. Uso agrícola da escória de siderurgia no Brasil—Estudos na cultura

da cana-de-açúcar. Jaboticabal,

[17] Pulz AL, Crusciol CAC, Lemos LB, Soratto RP. Influência de silicato e calcário na nutrição, produtividade e qualidade de batata sob deficiência hídrica. Revista Brasileira de Ciência do

[18] Carvalho-Pupatto JG, Büll LT, Crusciol CAC. Atributos químicos do

produtividade do arroz de acordo com a

[19] Corrêa JC, Büll LT, Crusciol CAC, Fernandes DM, Peres MGM. Aplicação superficial de diferentes fontes de corretivos no crescimento radicular e produtividade da aveia preta. Revista Brasileira de Ciência do Solo. 2008;321:

[20] Corrêa JC, Büll LT, Crusciol CAC, Tecchio MC. Aplicação superficial de escória, lama cal, lodos de esgoto e calcário na cultura da soja. Pesquisa Agropecuária Brasileira. 2008;43:

[21] Deus ACF, Büll LT. Eficiência de escórias de siderurgia na cultura do

solo, crescimento radicular e

aplicação de escórias. Pesquisa Agropecuária Brasileira. 2004;39:

1213-1218

583-1590

1209-1219

61

Funep. 2001. 68 p

Solo. 2008;32:1651-1659

10.5897/ajar2013.6940

Técnico 6

[9] Brasil, Ministério da Agricultura. Secretaria Nacional de Defesa Agropecuária. Portaria No. 31, de 8 de junho de 1986. Determina as características físicas, PN e PRNT mínimas dos corretivos da acidez do solo: Classifica os calcários agrícolas em função do PRNT e determina como será calculado o PRNT. Diário Oficial, Brasília; 14 de junho de 1986. seção 1. p. 10.790

[10] Brasil, Instrução Normativa SDA no. 27, de 05 de junho de 2006 (Alterada pela IN SDA no. 7, de 12/04/2016, republicada em 02/05/2016). Os fertilizantes, corretivos, inoculantes e biofertilizantes, para serem produzidos, importados ou comercializados, deverão atender aos limites estabelecidos nesta Instrução Normativa no que se refere às concentrações máximas admitidas para agentes fitotóxicos, patogênicos ao homem, animais e plantas, metais pesados tóxicos, pragas e ervas daninhas. Brasília: Diário Oficial da República Federativa do Brasil; 2006

[11] Deus ACF, Bull LT, Correa JC, Villas Boas RL. Nutrient accumulation and biomass production of alfalfa after soil amendment with silicates. Revista Ceres. 2014;61:406-413. DOI: 10.1590/ S0034-737X2014000300016

[12] Mantovani JR, Campos GM, Silva AB, Marques DJ, Putti FF, Langraf PRC, et al. Steel slag to correct soil acidity and as silicon source in coffee plants. African Journal of Agricultural Research. 2016;11:543-550. DOI: 10.5897/ajar2015.10535

[13] Souza RTX, Korndörfer GH. Slag efficacy as a lime and silicon source for rice crops trough the biological method. Journal of Plant Nutrition. 2010;33: 1103-1111

The Comprehensive Utilization of Steel Slag in Agricultural Soils DOI: http://dx.doi.org/10.5772/intechopen.81440

[14] Nolla A, Korndörfer GH, Silva CAT, Silva TRB, Zucarelli V, Silva MAG. Correcting soil acidity with the use of slags. African Journal of Agricultural Research. 2013;8:5174-5180. DOI: 10.5897/ajar2013.6940

References

[1] Das B, Prakash S, Reddy PSR, Misra VN. An overview of utilization of slag and sludge from steel industries. Resources, Conservation and Recycling.

Recovery and Utilization of Metallurgical Solid Waste

Agricola. 1996;53:211-216. DOI: 10.1590/

[9] Brasil, Ministério da Agricultura. Secretaria Nacional de Defesa

Agropecuária. Portaria No. 31, de 8 de

[10] Brasil, Instrução Normativa SDA no. 27, de 05 de junho de 2006 (Alterada pela IN SDA no. 7, de 12/04/2016, republicada em 02/05/2016). Os fertilizantes, corretivos, inoculantes e biofertilizantes, para serem produzidos, importados ou comercializados, deverão atender aos limites estabelecidos nesta Instrução Normativa no que se refere às concentrações máximas admitidas para agentes fitotóxicos, patogênicos ao homem, animais e plantas, metais pesados tóxicos, pragas e ervas daninhas. Brasília: Diário Oficial da República Federativa do Brasil; 2006

[11] Deus ACF, Bull LT, Correa JC, Villas Boas RL. Nutrient accumulation and biomass production of alfalfa after soil amendment with silicates. Revista Ceres. 2014;61:406-413. DOI: 10.1590/

[12] Mantovani JR, Campos GM, Silva AB, Marques DJ, Putti FF, Langraf PRC, et al. Steel slag to correct soil acidity and as silicon source in coffee plants. African Journal of Agricultural Research. 2016;11:543-550. DOI:

[13] Souza RTX, Korndörfer GH. Slag efficacy as a lime and silicon source for rice crops trough the biological method. Journal of Plant Nutrition. 2010;33:

S0034-737X2014000300016

10.5897/ajar2015.10535

1103-1111

S0103-90161996000200003

junho de 1986. Determina as características físicas, PN e PRNT mínimas dos corretivos da acidez do solo: Classifica os calcários agrícolas em função do PRNT e determina como será calculado o PRNT. Diário Oficial, Brasília; 14 de junho de 1986. seção 1.

p. 10.790

[2] Alcarde JA, Rodella AA. Qualidade e legislação de fertilizantes e corretivos. In: Curi N, Marques JJ, Guilherme LRG, Lima JM, Lopes AS, Alvares VVH, editors. Tópicos em Ciência do Solo. Sociedade Brasileira de Ciência do Solo;

[3] Babu T, Tubana B, Paye W, Kanke Y, Datnoff L. Establishing soil silicon test procedure and critical silicon level for rice in Louisiana soils. Communications in Soil Science and Plant Analysis. 2016:

[4] Yi H, Xu G, Cheng H, Wang J, Wan Y, Chen H. An overview of utilization of steel slag. Procedia Environmental Sciences. 2012;16:791-801. DOI: 10.1016/j.proenv.2012.10.108

[5] Shi C. Steel slag its production, processing, characteristics, and cementitious properties. Journal of Materials in Civil Engineering. 2004;16: 230-236. DOI: 10.1002/chin.200522249

[6] Torkashvand AM, Sedaghathoor S. Converter slag as a liming agent in the

International Journal of Agriculture and

[7] Deus ACF. Aplicação de corretivos de acidez do solo na implantação do sistema plantio direto [thesis]. Botucatu: Faculdade de Ciências Agronômicas de Botucatu—Universidade Estadual Paulista Júlio de Mesquita Filho; 2014

[8] Alcarde JC, Rodella AA. Avaliação química de corretivos de acidez para fins agrícolas: uma nova proposição. Scientia

amelioration of acidic soils.

Biology. 2007;9:715-720

60

2007;50:40-57. DOI: 10.1016/j.

resconrec.2006.05.008

2003. pp. 291-334

1532-2416

[15] Alcarde JC. Corretivos da acidez do solo: Características e interpretações técnicas. São Paulo—SP: Associação nacional para difusão de adubos e corretivos (ANDA); 1992. 62 p. Boletim Técnico 6

[16] Prado RM, Fernandes FM, Natale W. Uso agrícola da escória de siderurgia no Brasil—Estudos na cultura da cana-de-açúcar. Jaboticabal, Funep. 2001. 68 p

[17] Pulz AL, Crusciol CAC, Lemos LB, Soratto RP. Influência de silicato e calcário na nutrição, produtividade e qualidade de batata sob deficiência hídrica. Revista Brasileira de Ciência do Solo. 2008;32:1651-1659

[18] Carvalho-Pupatto JG, Büll LT, Crusciol CAC. Atributos químicos do solo, crescimento radicular e produtividade do arroz de acordo com a aplicação de escórias. Pesquisa Agropecuária Brasileira. 2004;39: 1213-1218

[19] Corrêa JC, Büll LT, Crusciol CAC, Fernandes DM, Peres MGM. Aplicação superficial de diferentes fontes de corretivos no crescimento radicular e produtividade da aveia preta. Revista Brasileira de Ciência do Solo. 2008;321: 583-1590

[20] Corrêa JC, Büll LT, Crusciol CAC, Tecchio MC. Aplicação superficial de escória, lama cal, lodos de esgoto e calcário na cultura da soja. Pesquisa Agropecuária Brasileira. 2008;43: 1209-1219

[21] Deus ACF, Büll LT. Eficiência de escórias de siderurgia na cultura do

feijoeiro em sistema de semeadura direta. Ciência Rural. 2013;43:1783-1789

[22] Correa JC, Freitag EE, Büll LT, Crusciol CAC, Fernandes DM, Marcelino R. Aplicação superficial de calcário e diferentes resíduos em soja cultivada no sistema plantio direto. Bragantia. 2009;68:1059-1068. DOI: 10.1590/S0006-87052009000 400027

[23] Brassioli FB, Prado RM, Fernandes FM. Avaliação agronômica da escória de siderurgia na cana-de-açúcar durante cinco ciclos de produção. Bragantia. 2009;68:381-387

[24] Flower KC, Crabtree WL. Soil pH change after surface application of lime related to the levels of soil disturbance caused by no-tillage seeding machinery. Field Crops Research. 2011;121:75-87. DOI: 10.1016/j.fcr.2010.11.014

[25] Corrêa JC, Büll LT, Crusciol CAC, Marcelino R, Mauad M. Correção da acidez e mobilidade de íons em Latossolo com aplicação superficial de escória, lama cal, lodos de esgoto e calcário. Pesquisa Agropecuária Brasileira. 2007;42:1307-1317

[26] Castro GSA, Crusciol CAC. Effects of superficial liming and silicate application on soil fertility and crop yield under rotation. Geoderma. 2013; 195–196:234-242

[27] Castro GSA, Crusciol CAC. Yield and mineral nutrition of soybean, maize, and Congo signal grass as affected by limestone and slag. Pesquisa Agropecuária Brasileira. 2013;48: 673-681. DOI: 10.1590/ S0100-204X2013000600013

[28] Castro GSA, Crusciol CAC, Costa CHM, Ferrari Neto J, Mancuso MAC. Surface application of limestone and calcium-magnesium silicate in a tropical no-tillage system. Journal of Soil Science and Plant Nutrition. 2016;16:362-379.

DOI: 10.4067/S0718-951620160050 00034

[29] Pereira HS, Gama AJM, Camargo MS, Korndörfer GH. Reatividade de escórias silicatadas da indústria siderúrgica. Ciência e Agrotecnologia. 2010;34:382-390

[30] Prado RM, Fernandes FM. Efeito da escória de siderurgia e calcário na disponibilidade de fósforo de um Latossolo Vermelho-Amarelo cultivado com cana-deaçúcar. Pesquisa Agropecuária Brasileira. 2001;36: 1199-1204

[31] Amaral Sobrinho NMB, Velloso ACX, Oliveira C. Solubilidade de metais pesados em solo tratado com resíduo siderúrgico. Revista Brasileira de Ciência do Solo. 1997;21:9-16

[32] Corrêa JC, Büll LT, Paganini WS, Guerrini IA. Disponibilidade de metais pesados em Latossolo com aplicação superficial de escória, lama cal, lodos de esgoto e calcário. Pesquisa Agropecuária Brasileira. 2008;43:411-419

[33] Sposito G. The Chemistry of Soils. New York: Oxford University Press; 2008. p. 329

[34] Silveira MLA, Alleoni LRF, Guilherme LRG. Biosolids and heavy metals in soils. Scientia Agricola. 2003; 60:793-806

[35] Deren CW, Datnoff LE, Snyder GH, Martin FG. Silicon concentration, disease response, and yield components of rice genotypes grown on flooded organic histosols. Crop Science. 1994;34: 733-737

[36] Korndörfer GH, Pereira HS, de Camargo MS. Silicatos de cálcio e magnésio na agricultura. Uberlândia: GPSi; 2003. p. 15. Boletim Técnico no 1

[37] Tavakkoli E, English P, Guppy CN. Interaction of silicon and phosphorus

mitigate manganese toxicity in rice in a highly weathered soil. Communications in Soil Science and Plant Analysis. 2011; 42:503-513

[38] Liang Y, Sun W, Zhu Y-G, Christie P. Mechanisms of silicon-mediated alleviation of abiotic stresses in higher plants: A review. Environmental Pollution, Barking. 2007;147:422-428

[39] Ning D, Song A, Fan F, Li Z, Liang Y. Effects of slag-based silicon fertilizer on rice growth and brown-spot resistance. PLoS One. 2014;9(7): e102681. DOI: 10.1371/journal. pone.0102681

[40] Ning D, Liang Y, Liu Z, Xiao J, Duan A. Impacts of steel-slag-based silicate fertilizer on soil acidity and silicon availability and metalsimmobilization in a paddy soil. PLoS One. 2016;11(12):e0168163. DOI: 10.1371/journal.pone.0168163

[41] Barbosa Filho MP, Zimmermann FJP, Silva OF. Influence of calcium silicate slag on soil acidity and upland rice grain yield. Ciência agrotecnologia. 2004;28:323-331. DOI: 10.1590/ S1413-70542004000200011

[42] Fonseca IM, Prado RM, Vidal AA, Nogueira TAR. Efeito da escória, calcário e nitrogênio na absorção de silício e na produção de capim-marandu. Bragantia. 2009;68:221-232. DOI: 10.1590/S0006-87052009000100024

**63**

**Chapter 5**

**Abstract**

*and Wensheng Qiu*

environment friendly

**1. Introduction**

Comprehensive Utilization of

Iron-Bearing Converter Wastes

*Hu Long, Dong Liu, Lie-Jun Li, Ming-Hua Bai, Yanzhong Jia* 

Basic oxygen furnace (BOF) sludge is composed of not only valuable iron but also impurities like Zn, Pb, and some alkaline oxides. It is collected from wet cleaning system in steelmaking plants. How to deal with these double identity wastes? Will the traditional landfill treatments result in environmental pollution? What technologies have been developed recently, and is it actually useful? In this chapter, physical-chemical properties and mineralogical phases of converter sludge were characterized, and different recycling technologies were introduced. The proven metalized pellet-producing process would be highlighted that green pellets made from iron-bearing sludge are dried and preheated in a traveling grate firstly, and then reduced at high temperature in a rotary kiln or a rotary hearth furnace (RHF) to get direct reduced iron (DRI), served as a good iron source for blast furnace.

**Keywords:** BOF sludge, iron bearing, metalized pellet, direct reduced iron,

more and more attention of metallurgical researchers.

BOF sludge is collected from wet cleaning system in steelmaking plants. It is composed of not only valuable iron but also impurities like Zn, Pb, and some alkaline oxides [1–3]. Traditional landfill treatments inevitably result in environmental pollution because of the contained heavy metal and the high pH values of water-absorbed soil [4, 5]. Sintering is another recycling way to treat the sludge as raw material for sintering ore and fed to the blast furnace (BF). However, it leads to the circulation and accumulation of zinc in BF [6, 7]. To decrease the negative effects on BF production and surrounding environment, new recycling technologies have been developed, one proven of which is the metalized pellet-producing process, that green pellets made from iron-bearing sludge are dried and preheated in a traveling grate firstly, and then reduced at high temperature in a rotary kiln or a rotary hearth furnace (RHF) to get direct reduced iron (DRI), served as a good iron source for electric arc furnace (EAF) or BF [8–10]. It is an appropriate method to recycle the valuable iron and remove the harmful elements, simultaneously improve the burden structure of BF, which attracts

Green pellets should be dried before charged into the consequent preheating and reduction process, or else they are easily to be cracked or pulverized owing to drastic volatilization of moisture at a high temperature, and results in the significant drop of the permeability, which will eventually lower the metallization rate of the

## **Chapter 5**

DOI: 10.4067/S0718-951620160050

Recovery and Utilization of Metallurgical Solid Waste

mitigate manganese toxicity in rice in a highly weathered soil. Communications in Soil Science and Plant Analysis. 2011;

[38] Liang Y, Sun W, Zhu Y-G, Christie P. Mechanisms of silicon-mediated alleviation of abiotic stresses in higher plants: A review. Environmental Pollution, Barking. 2007;147:422-428

[39] Ning D, Song A, Fan F, Li Z, Liang Y. Effects of slag-based silicon fertilizer on rice growth and brown-spot

resistance. PLoS One. 2014;9(7): e102681. DOI: 10.1371/journal.

[40] Ning D, Liang Y, Liu Z, Xiao J, Duan A. Impacts of steel-slag-based silicate fertilizer on soil acidity and silicon availability and metalsimmobilization in a paddy soil. PLoS One. 2016;11(12):e0168163. DOI: 10.1371/journal.pone.0168163

[41] Barbosa Filho MP, Zimmermann FJP, Silva OF. Influence of calcium silicate slag on soil acidity and upland rice grain yield. Ciência agrotecnologia.

[42] Fonseca IM, Prado RM, Vidal AA, Nogueira TAR. Efeito da escória, calcário e nitrogênio na absorção de silício e na produção de capim-marandu. Bragantia. 2009;68:221-232. DOI: 10.1590/S0006-87052009000100024

2004;28:323-331. DOI: 10.1590/ S1413-70542004000200011

42:503-513

pone.0102681

[29] Pereira HS, Gama AJM, Camargo MS, Korndörfer GH. Reatividade de escórias silicatadas da indústria siderúrgica. Ciência e Agrotecnologia.

[30] Prado RM, Fernandes FM. Efeito da escória de siderurgia e calcário na disponibilidade de fósforo de um Latossolo Vermelho-Amarelo cultivado

com cana-deaçúcar. Pesquisa Agropecuária Brasileira. 2001;36:

[31] Amaral Sobrinho NMB, Velloso ACX, Oliveira C. Solubilidade de metais pesados em solo tratado com resíduo siderúrgico. Revista Brasileira de Ciência do Solo. 1997;21:9-16

[32] Corrêa JC, Büll LT, Paganini WS, Guerrini IA. Disponibilidade de metais pesados em Latossolo com aplicação superficial de escória, lama cal, lodos de esgoto e calcário. Pesquisa Agropecuária

[33] Sposito G. The Chemistry of Soils. New York: Oxford University Press;

[35] Deren CW, Datnoff LE, Snyder GH, Martin FG. Silicon concentration, disease response, and yield components of rice genotypes grown on flooded organic histosols. Crop Science. 1994;34:

[36] Korndörfer GH, Pereira HS, de Camargo MS. Silicatos de cálcio e magnésio na agricultura. Uberlândia: GPSi; 2003. p. 15. Boletim Técnico no 1

[37] Tavakkoli E, English P, Guppy CN. Interaction of silicon and phosphorus

Brasileira. 2008;43:411-419

[34] Silveira MLA, Alleoni LRF, Guilherme LRG. Biosolids and heavy metals in soils. Scientia Agricola. 2003;

2008. p. 329

60:793-806

733-737

62

00034

2010;34:382-390

1199-1204

## Comprehensive Utilization of Iron-Bearing Converter Wastes

*Hu Long, Dong Liu, Lie-Jun Li, Ming-Hua Bai, Yanzhong Jia and Wensheng Qiu*

#### **Abstract**

Basic oxygen furnace (BOF) sludge is composed of not only valuable iron but also impurities like Zn, Pb, and some alkaline oxides. It is collected from wet cleaning system in steelmaking plants. How to deal with these double identity wastes? Will the traditional landfill treatments result in environmental pollution? What technologies have been developed recently, and is it actually useful? In this chapter, physical-chemical properties and mineralogical phases of converter sludge were characterized, and different recycling technologies were introduced. The proven metalized pellet-producing process would be highlighted that green pellets made from iron-bearing sludge are dried and preheated in a traveling grate firstly, and then reduced at high temperature in a rotary kiln or a rotary hearth furnace (RHF) to get direct reduced iron (DRI), served as a good iron source for blast furnace.

**Keywords:** BOF sludge, iron bearing, metalized pellet, direct reduced iron, environment friendly

#### **1. Introduction**

BOF sludge is collected from wet cleaning system in steelmaking plants. It is composed of not only valuable iron but also impurities like Zn, Pb, and some alkaline oxides [1–3]. Traditional landfill treatments inevitably result in environmental pollution because of the contained heavy metal and the high pH values of water-absorbed soil [4, 5]. Sintering is another recycling way to treat the sludge as raw material for sintering ore and fed to the blast furnace (BF). However, it leads to the circulation and accumulation of zinc in BF [6, 7]. To decrease the negative effects on BF production and surrounding environment, new recycling technologies have been developed, one proven of which is the metalized pellet-producing process, that green pellets made from iron-bearing sludge are dried and preheated in a traveling grate firstly, and then reduced at high temperature in a rotary kiln or a rotary hearth furnace (RHF) to get direct reduced iron (DRI), served as a good iron source for electric arc furnace (EAF) or BF [8–10]. It is an appropriate method to recycle the valuable iron and remove the harmful elements, simultaneously improve the burden structure of BF, which attracts more and more attention of metallurgical researchers.

Green pellets should be dried before charged into the consequent preheating and reduction process, or else they are easily to be cracked or pulverized owing to drastic volatilization of moisture at a high temperature, and results in the significant drop of the permeability, which will eventually lower the metallization rate of the

products in the reduction furnace, or even make the production abnormal [11, 12]. Additionally, it has been reported that about 25% of energy for pellet induration is consumed for drying [12]. Thus, the improvement of the drying performance will be energy efficient, and also the drying mechanism of iron ore pellets made from BOF sludge is extremely important.

After dried and preheated, the mainstream approach dealing with pellets is baked first and then reduced by coal or reduction gas; another way is directly reduced so-called one-step method, one proven of which is the grate-rotary kiln process with high heat transfer efficiency, where the preheated iron-bearing material instead of fired oxide pellets directly reacts with the reductant of coal at high temperature to get direct reduced iron (DRI) [13, 14]. Compared with the traditional two-step rotary kiln, the new process is simplified and the risk of kiln accretion is reduced, because of the decreasing degradation without phase transferring from hematite to magnetite, which has been developed rapidly in China [15–17]. Metalized pellets could be used as burden for electric arc furnace (EAF) or BF, and the reduction degree, compressive strength and dezincification rate are considered as three important indicators [18–21]. They were energetically investigated by metallurgical researchers recently [9, 22, 23]. Many significant researches have been carried out to understand the reduction behavior of iron-bearing materials.

In this chapter, performances of pellets prepared from the BOF sludge are briefly presented at first and then studies on drying characteristics and reduction behavior under different conditions are introduced and compared to provide scientific guidance for recycling of secondary iron-bearing resource from BOF wastes [24–26].

### **2. Brief process of metallized pellet production**

#### **2.1 Two-step method**

For traditional two-step method, oxidized pellets are prepared initially as raw materials for metallizing process, and then metallized pellets are produced through the direct reduction process, during which the temperature is below the melting point of the iron and the products referred to as direct reduced iron (DRI).

#### *2.1.1 Preparation of oxidized pellets*

The grate-rotary kiln producing line is considered and adopted as one of the most mature technologies, which has a strong adaptability to raw material and fuel, good quality, and low cost of production. The process consists of proportioning system, mixing, pelletizing system, green ball roller screen, and distribution, as well as grate-rotary kiln system for pellet indurations, finished product stock piling, and delivery system. The grate-kiln process flow is shown in **Figure 1**.

Concentrate fines are discharged to storage bins through the belt in the stockyard. Each concentrate store is equipped with disc feeder with frequency control and electric belt scale. Limestone and bentonite are delivered by tanker and then in a pneumatic transmission. Dust from multicyclone and electrostatic precipitators (ESP) for the main induced system is delivered by pneumatic transmission to dust bin. All the storage bins adopt weighing level gage to check material level in storage bin. The set value of charge ratio is automatically controlled and regulated by programmable logic controller (PLC) microprocessor. After all kinds of materials are compounded at a certain proportion, they are delivered directly to mixing room by the belt conveyor. Mixing room is usually equipped with a vertical mixer, which can mix materials both in micro- and macroway with high effectiveness, reliable operation, and simple maintenance. Materials mixed are

**65**

conveyor system.

*Process flow chart of grate-kiln pelletizing plant.*

**Figure 1.**

*Comprehensive Utilization of Iron-Bearing Converter Wastes*

delivered to pelletizing room by the belt conveyor. The belt conveyor is equipped with

Disk pelletizers are often adopted for preparing green pellets. Revolving speed and inclination of disk are adjustable to guarantee the quality. Roller screener is equipped for screening, and pellets with suitable size are delivered to the distributer system in chain grate room, while others that unqualified are returned by the return

Chain grate area is mainly consisted of shuttle-type distributor, wide belt conveyor, roller distributer, chain grate, combustion burner fan for chain grate, electric double-dumping ash valve, bucket elevator and belt conveyor, etc. Shuttle distributor discharges green pellet to wide belt conveyor under motion back and forth, and the wide belt conveyor with speed in frequency control delivers green pellets to roller distributing device. Qualified green pellets are dried and preheated in the chain grate, and delivered to rotary kiln for roasting. Chain grate is divided into four zones, which are up-draft drying zone, down-draft drying zone, preheat I zone, and preheat II zone, respectively. The thickness of material bed in chain grate is about 180– 200 mm, with the normal motion speed of 3.1 m/min. Pellets are first dried in the up-draft drying section by the recycle hot air in the temperature range of 160–250°C from the third cooling zone of annular cooler, which remove attached water in green pellets and to avoid pellets in the bottom of the grate bed from wetting. Temperature of hot returning gas from the annular cooler is in the range of 180–320°C, which can be mixed with cold air if necessary. In down-draft drying zone, 320–400°C recycle hot gas from the preheating II zone is pumped by hot-resistance draught fan across material layer from upper smoke shield, which makes green pellets dewater and dry, and can bear high-temperature stress and strain in 550–700°C in preheating I zone. The main induced draught fan is set to pump exhausted gas from air bellow, and eliminate it into atmosphere from electric precipitator. In preheating I zone, hot gas flow continues to dry green pellets through the material layer, and dried pellets begin to be oxidized, and the heat is derived from the hot exhausted gas of annular cooler II cooling zone. In preheating II zone, pellets are heated and oxidized further, and completely indurated, which makes pellets have a certain intensity, and can bear

moisture detector for check and control of water addition for palletizing.

*DOI: http://dx.doi.org/110.5772/intechopen.80329*

*Comprehensive Utilization of Iron-Bearing Converter Wastes DOI: http://dx.doi.org/110.5772/intechopen.80329*

*Recovery and Utilization of Metallurgical Solid Waste*

BOF sludge is extremely important.

products in the reduction furnace, or even make the production abnormal [11, 12]. Additionally, it has been reported that about 25% of energy for pellet induration is consumed for drying [12]. Thus, the improvement of the drying performance will be energy efficient, and also the drying mechanism of iron ore pellets made from

After dried and preheated, the mainstream approach dealing with pellets is baked first and then reduced by coal or reduction gas; another way is directly reduced so-called one-step method, one proven of which is the grate-rotary kiln process with high heat transfer efficiency, where the preheated iron-bearing material instead of fired oxide pellets directly reacts with the reductant of coal at high temperature to get direct reduced iron (DRI) [13, 14]. Compared with the traditional two-step rotary kiln, the new process is simplified and the risk of kiln accretion is reduced, because of the decreasing degradation without phase transferring from hematite to magnetite, which has been developed rapidly in China [15–17]. Metalized pellets could be used as burden for electric arc furnace (EAF) or BF, and the reduction degree, compressive strength and dezincification rate are considered as three important indicators [18–21]. They were energetically investigated by metallurgical researchers recently [9, 22, 23]. Many significant researches have been

carried out to understand the reduction behavior of iron-bearing materials.

**2. Brief process of metallized pellet production**

**2.1 Two-step method**

*2.1.1 Preparation of oxidized pellets*

In this chapter, performances of pellets prepared from the BOF sludge are briefly presented at first and then studies on drying characteristics and reduction behavior under different conditions are introduced and compared to provide scientific guidance for recycling of secondary iron-bearing resource from BOF wastes [24–26].

For traditional two-step method, oxidized pellets are prepared initially as raw materials for metallizing process, and then metallized pellets are produced through the direct reduction process, during which the temperature is below the melting point of the iron and the products referred to as direct reduced iron (DRI).

The grate-rotary kiln producing line is considered and adopted as one of the most mature technologies, which has a strong adaptability to raw material and fuel, good quality, and low cost of production. The process consists of proportioning system, mixing, pelletizing system, green ball roller screen, and distribution, as well as grate-rotary kiln system for pellet indurations, finished product stock piling,

Concentrate fines are discharged to storage bins through the belt in the stockyard. Each concentrate store is equipped with disc feeder with frequency control and electric belt scale. Limestone and bentonite are delivered by tanker and then in a pneumatic transmission. Dust from multicyclone and electrostatic precipitators (ESP) for the main induced system is delivered by pneumatic transmission to dust bin. All the storage bins adopt weighing level gage to check material level in storage bin. The set value of charge ratio is automatically controlled and regulated by programmable logic controller (PLC) microprocessor. After all kinds of materials are compounded at a certain proportion, they are delivered directly to mixing room by the belt conveyor. Mixing room is usually equipped with a vertical mixer, which can mix materials both in micro- and macroway with high effectiveness, reliable operation, and simple maintenance. Materials mixed are

and delivery system. The grate-kiln process flow is shown in **Figure 1**.

**64**

**Figure 1.** *Process flow chart of grate-kiln pelletizing plant.*

delivered to pelletizing room by the belt conveyor. The belt conveyor is equipped with moisture detector for check and control of water addition for palletizing.

Disk pelletizers are often adopted for preparing green pellets. Revolving speed and inclination of disk are adjustable to guarantee the quality. Roller screener is equipped for screening, and pellets with suitable size are delivered to the distributer system in chain grate room, while others that unqualified are returned by the return conveyor system.

Chain grate area is mainly consisted of shuttle-type distributor, wide belt conveyor, roller distributer, chain grate, combustion burner fan for chain grate, electric double-dumping ash valve, bucket elevator and belt conveyor, etc. Shuttle distributor discharges green pellet to wide belt conveyor under motion back and forth, and the wide belt conveyor with speed in frequency control delivers green pellets to roller distributing device. Qualified green pellets are dried and preheated in the chain grate, and delivered to rotary kiln for roasting. Chain grate is divided into four zones, which are up-draft drying zone, down-draft drying zone, preheat I zone, and preheat II zone, respectively. The thickness of material bed in chain grate is about 180– 200 mm, with the normal motion speed of 3.1 m/min. Pellets are first dried in the up-draft drying section by the recycle hot air in the temperature range of 160–250°C from the third cooling zone of annular cooler, which remove attached water in green pellets and to avoid pellets in the bottom of the grate bed from wetting. Temperature of hot returning gas from the annular cooler is in the range of 180–320°C, which can be mixed with cold air if necessary. In down-draft drying zone, 320–400°C recycle hot gas from the preheating II zone is pumped by hot-resistance draught fan across material layer from upper smoke shield, which makes green pellets dewater and dry, and can bear high-temperature stress and strain in 550–700°C in preheating I zone. The main induced draught fan is set to pump exhausted gas from air bellow, and eliminate it into atmosphere from electric precipitator. In preheating I zone, hot gas flow continues to dry green pellets through the material layer, and dried pellets begin to be oxidized, and the heat is derived from the hot exhausted gas of annular cooler II cooling zone. In preheating II zone, pellets are heated and oxidized further, and completely indurated, which makes pellets have a certain intensity, and can bear

impact without breakage when falling to rotary kiln from chain grate in the motion of rotary kiln. Heat source comes from 900 to 1180°C hot air flow in rotary tail. A hole is left and sealed by fireclay brick in the partition wall between the first and second preheating zones. The hole can be opened in the case of thermal compensation. Hot exhausted gas in preheating I zone through collection header pipe of air bellow two sides and hot exhausted gas in down-draft drying zone are together discharged by electrostatic precipitator, main induced draught fan, and chimney. Chimney and valve are set at the top of the shield in preheating II zone, which is used for waste gas blowing off during furnace baking and emergency failure operation. Burners are installed in the cover of chain grate for thermal compensation. Preheated pellets get enough compressive, and then enter rotary kiln through kiln tail chute.

The rotary head is equipped with natural combustion apparatus with adjustable frame shape and length. Pellets are roasted while rotating in the kiln, so that the uniformity is assured. Baking temperature in rotary kiln is 1250–1320°C, revolving speed of rotary kiln is adjusted according to raw material differences to obtain enough retention time, and pellet quality. Liner made from precast brick and refractory castables makes kiln service with better thermal shock resistance and wear resistance and heat-shielding performance. An infrared simplified scanning temperature measurement system is adopted to detect and control the temperature inside. Roasted pellets are screened and discharged to receiving hopper of annular cooler.

Annular cooler consists of rotating part, air bellow, transmission device, rack, upper shield, and the system of variable-frequency adjustable-speed. It is mainly divided into four areas: I cooling zone, 900–1100°C of hot air is directly led to rotary kiln and used to raise temperature in kiln atmosphere; II cooling zone, 500–700°C of hot air returns to upper shield in preheating I zone of chain grate; III cooling zone, 180–320°C of hot air is led to up-draft drying section in grate; IV cooling section, 85–105°C of hot air is dedusted and exhausted through the chimney, with emission dust concentration below 50 mg/Nm3 . Fans are adopted to cool down pellets step by step and control the temperature of hot wind, and the majority of the heat generated during this cooling process is effectively reutilized. Pellets below 120°C are discharged through the hopper to belt conveyor, and then delivered out.

#### *2.1.2 Preparation of metallized pellets*

The attempts to develop large-scale direct processes have embraced practically every known type of apparatus suitable for the purpose including pot furnaces, reverberatory furnaces, shaft furnaces, rotary and stationary kilns, rotary hearth furnaces, electric furnaces, various combination furnaces, fluidized bed reactors, and plasma reactors. Many reducing agents including coal, coke, graphite, char, distillation residues, fuel oil, tar, producer gas, coal gas, water gas, and hydrogen have also been tried. For handling the BOF wastes, coal-based direct reduction technologies including the rotary kiln or the rotary hearth furnace (RHF) are often adopted in consideration of better material adaptability as well as for steady and reliable operation.

The representative two-step coal-based rotary kiln reduction process to produce sponge iron is given below including major technical parameters, types of equipment used, and the flow of materials through the plant. It is mainly composed of coal shed, iron raw material shed, coal screening building, proportioning building, rotary kiln-cooling building, etc. Schematic flowsheet of this rotary-kiln sponge iron plant is shown in **Figure 2** [27].

The lump ore or pellet is transported into DRI plant by dump trucks. The iron raw material feeds the belt conveyor by wheel loader then delivered to the proportioning building. The reductant (coal) is transported into DRI plant by dump trucks. The

**67**

**Figure 2.**

*Comprehensive Utilization of Iron-Bearing Converter Wastes*

capacity of the reductant (coal) storing yard is for about 16 days. Coal is fed into the belt conveyor by wheel loader and then delivered to the coal screening building for classification. The grain size of reductant is 0–50 mm. According to the process requirement, the grain size of the coal fed at the head of rotary kiln is 3–25 mm and at the tail is 25–35 mm. The coal is separated into four granularities: 0–3, 3–25, 25–35, and 35–50 mm by linear screen. The coal with grain size 3–25 mm will be delivered to the coal hopper at the head of the rotary kiln, coal with grain size 25–35 mm is delivered to the coal bin in the proportioning building by belt conveyor, and coals with grain sizes 0–3 and 35–50 mm are delivered to power plant by truck. The desulfurizer (limestone) is transported into DRI plant by dump trucks and discharged into the receiving hopper in the proportioning building, and then delivered to the limestone bins in the proportioning building by steeply belt conveyor. The proportioning of iron raw material, limestone, and coal is completed in the proportioning building.

The rotary kiln is one of the main equipments used to produce directly reduced iron products. The mixed material fed into the rotary kiln is heated up to a certain temperature in the kiln, and then the reduction reaction will take place. Detailed process is as follows. The iron raw materials, coal, and limestone used for reduction are fed at the head and tail of the rotary kiln separately. The granular coal injection gunner and the ignitor based on diesel oil will be settled in the head of rotary kiln. The diesel oil ignitor is set to increase temperature up to the range of 600–800°C. The grain size of coal fed at the head is 3–25 mm, which is injected to the rotary kiln by granular coal injection gunner. The grain size of coal fed into the rotary kiln at the tail is 25–35 mm, together with limestone and iron raw material by belt scale. According to the chemical equation C + CO2 = 2CO, the CO will react with the oxygen contained in the pellet. The rest of the CO is burnt with the secondary injecting hot air to heat up the rotary kiln and the pellets. A series of chemical reactions take place with the iron raw materials, reductant, and desulfurizer, and then the oxidized pellets are reduced to metallized pellets, so-called sponge iron. The sponge iron is discharged to the cooler drum from the end of the rotary kiln. The temperature inside the rotary kiln is in the range of 1000–1100°C, and the retention time inside is about 5–9 h. After that, the sponge iron at high temperature

is discharged to the fixed screen and sent to the cooler drum to be cooled.

The cooler drum is self-sealed with credible sealing device at the feed end and discharge end, and operated with micropositive pressure with the inner part isolated from the outside environment (air). To avoid oxidation, the product is cooled

The belt scale is adopted to make proportioning accurate.

*DOI: http://dx.doi.org/110.5772/intechopen.80329*

*Schematic flowsheet of rotary-kiln sponge iron process.*

*Comprehensive Utilization of Iron-Bearing Converter Wastes DOI: http://dx.doi.org/110.5772/intechopen.80329*

**Figure 2.**

*Recovery and Utilization of Metallurgical Solid Waste*

dust concentration below 50 mg/Nm3

*2.1.2 Preparation of metallized pellets*

iron plant is shown in **Figure 2** [27].

impact without breakage when falling to rotary kiln from chain grate in the motion of rotary kiln. Heat source comes from 900 to 1180°C hot air flow in rotary tail. A hole is left and sealed by fireclay brick in the partition wall between the first and second preheating zones. The hole can be opened in the case of thermal compensation. Hot exhausted gas in preheating I zone through collection header pipe of air bellow two sides and hot exhausted gas in down-draft drying zone are together discharged by electrostatic precipitator, main induced draught fan, and chimney. Chimney and valve are set at the top of the shield in preheating II zone, which is used for waste gas blowing off during furnace baking and emergency failure operation. Burners are installed in the cover of chain grate for thermal compensation. Preheated pellets get

The rotary head is equipped with natural combustion apparatus with adjustable frame shape and length. Pellets are roasted while rotating in the kiln, so that the uniformity is assured. Baking temperature in rotary kiln is 1250–1320°C, revolving speed of rotary kiln is adjusted according to raw material differences to obtain enough retention time, and pellet quality. Liner made from precast brick and refractory castables makes kiln service with better thermal shock resistance and wear resistance and heat-shielding performance. An infrared simplified scanning temperature measurement system is adopted to detect and control the temperature inside. Roasted

Annular cooler consists of rotating part, air bellow, transmission device, rack, upper shield, and the system of variable-frequency adjustable-speed. It is mainly divided into four areas: I cooling zone, 900–1100°C of hot air is directly led to rotary kiln and used to raise temperature in kiln atmosphere; II cooling zone, 500–700°C of hot air returns to upper shield in preheating I zone of chain grate; III cooling zone, 180–320°C of hot air is led to up-draft drying section in grate; IV cooling section, 85–105°C of hot air is dedusted and exhausted through the chimney, with emission

step and control the temperature of hot wind, and the majority of the heat generated during this cooling process is effectively reutilized. Pellets below 120°C are

The attempts to develop large-scale direct processes have embraced practically every known type of apparatus suitable for the purpose including pot furnaces, reverberatory furnaces, shaft furnaces, rotary and stationary kilns, rotary hearth furnaces, electric furnaces, various combination furnaces, fluidized bed reactors, and plasma reactors. Many reducing agents including coal, coke, graphite, char, distillation residues, fuel oil, tar, producer gas, coal gas, water gas, and hydrogen have also been tried. For handling the BOF wastes, coal-based direct reduction technologies including the rotary kiln or the rotary hearth furnace (RHF) are often adopted in consideration of better material adaptability as well as for steady and

The representative two-step coal-based rotary kiln reduction process to produce sponge iron is given below including major technical parameters, types of equipment used, and the flow of materials through the plant. It is mainly composed of coal shed, iron raw material shed, coal screening building, proportioning building, rotary kiln-cooling building, etc. Schematic flowsheet of this rotary-kiln sponge

The lump ore or pellet is transported into DRI plant by dump trucks. The iron raw material feeds the belt conveyor by wheel loader then delivered to the proportioning building. The reductant (coal) is transported into DRI plant by dump trucks. The

discharged through the hopper to belt conveyor, and then delivered out.

. Fans are adopted to cool down pellets step by

enough compressive, and then enter rotary kiln through kiln tail chute.

pellets are screened and discharged to receiving hopper of annular cooler.

**66**

reliable operation.

*Schematic flowsheet of rotary-kiln sponge iron process.*

capacity of the reductant (coal) storing yard is for about 16 days. Coal is fed into the belt conveyor by wheel loader and then delivered to the coal screening building for classification. The grain size of reductant is 0–50 mm. According to the process requirement, the grain size of the coal fed at the head of rotary kiln is 3–25 mm and at the tail is 25–35 mm. The coal is separated into four granularities: 0–3, 3–25, 25–35, and 35–50 mm by linear screen. The coal with grain size 3–25 mm will be delivered to the coal hopper at the head of the rotary kiln, coal with grain size 25–35 mm is delivered to the coal bin in the proportioning building by belt conveyor, and coals with grain sizes 0–3 and 35–50 mm are delivered to power plant by truck. The desulfurizer (limestone) is transported into DRI plant by dump trucks and discharged into the receiving hopper in the proportioning building, and then delivered to the limestone bins in the proportioning building by steeply belt conveyor. The proportioning of iron raw material, limestone, and coal is completed in the proportioning building. The belt scale is adopted to make proportioning accurate.

The rotary kiln is one of the main equipments used to produce directly reduced iron products. The mixed material fed into the rotary kiln is heated up to a certain temperature in the kiln, and then the reduction reaction will take place. Detailed process is as follows. The iron raw materials, coal, and limestone used for reduction are fed at the head and tail of the rotary kiln separately. The granular coal injection gunner and the ignitor based on diesel oil will be settled in the head of rotary kiln. The diesel oil ignitor is set to increase temperature up to the range of 600–800°C. The grain size of coal fed at the head is 3–25 mm, which is injected to the rotary kiln by granular coal injection gunner. The grain size of coal fed into the rotary kiln at the tail is 25–35 mm, together with limestone and iron raw material by belt scale. According to the chemical equation C + CO2 = 2CO, the CO will react with the oxygen contained in the pellet. The rest of the CO is burnt with the secondary injecting hot air to heat up the rotary kiln and the pellets. A series of chemical reactions take place with the iron raw materials, reductant, and desulfurizer, and then the oxidized pellets are reduced to metallized pellets, so-called sponge iron. The sponge iron is discharged to the cooler drum from the end of the rotary kiln. The temperature inside the rotary kiln is in the range of 1000–1100°C, and the retention time inside is about 5–9 h. After that, the sponge iron at high temperature is discharged to the fixed screen and sent to the cooler drum to be cooled.

The cooler drum is self-sealed with credible sealing device at the feed end and discharge end, and operated with micropositive pressure with the inner part isolated from the outside environment (air). To avoid oxidation, the product is cooled down below 120°C indirectly by spraying water to the outside surface of the cooler drum. The material will stay inside for about 25–40 min.

The cooled product is delivered to the product sorting room to screening and classification in order to separate the DRI, magnetic powder, nonmagnetic powder, and return coal fines. The product discharged from the cooler drum is delivered to the screen equipment and separated into two granularities: >4 and <4 mm. To minimize the iron content in nonmagnetic powder, the product of >4 mm will be proceed in three steps in magnetic separator. The magnetic material discharged from the magnetic separator is fed to the steel melt shop. The nonmagnetic material is discharged from the bottom of magnetic separator, regarded as return coal, and delivered to proportioning building. The product of <4 mm is separated in two serial elutriator for pneumatic classification: the light one such as ash is dedusted, and the heavier one is pneumatic delivered to the single magnetic separator. After magnetic classification, the nonmagnetic powder is delivered to nonmagnetic bin by belt conveyor and bucket elevator and then transferred by trucks; the magnetic material will be separated in elutriator, delivered to magnetic bin by belt conveyor and then pressed into block, and finally delivered to the steel melt shop too.

#### **2.2 One-step method**

The "one-step" method is mainly composed of concentrate pelletizing—preheating—direct reduction (coal-based kiln reduction/rotary hearth furnace)—cooling. Compared with the traditional two-step method, the preheated pellets with certain intensity are directly delivered to the direct reduction furnace, which not only shortens the process line with satisfactory product quality, but also saves the energy.

The key equipment reform and technologies of one-step kiln process are primarily researched and applied into operation in China. Reduction behavior of two kinds of pellets using noncoking coal as reductant is studied and compared. The one is preheated pellet made of magnetite concentrate with composite binder, and the other is fired oxide pellets containing bentonite as binder [15]. Reducibility, compress strength, porosity, and microphases evolution are measured. Results show that preheated pellets possess much better reducibility than fired oxide pellets, which is ascribed to their higher effective diffusivity due to higher porosity. The compressive strength increases obviously after 30 min reduction and achieves a high value at the end of reduction, while the value of metalized pellets from reduction of oxidized pellets is much lower, because of more cracks and fractures formed. Xinjiang magnetite concentrate in China was studied by one-step process for direct reduction. The results show that for Xinjiang magnetite assaying with 69.21% Fe, damp milling and adding agent can improve the quality of green balls obviously. After drying, green balls are preheated at 800°C for 10 min, pellets with compressive strength of 581 N/pellet are achieved, preheated pellets were directly reduced at 1050°C for 80 min, and directly reduced iron assaying 90.33% of total iron and 85.05% of metallic iron and 94.15% of metallization degree are achieved. Compared with the traditional direct reduction of fired oxide pellets in coal-based rotary kilns, one-step process for direct reduction can avoid high-temperature oxidation of pellets at 1150–1300°C, and possess some advantages such as greater economic profit and good quality of direct reduced iron [28]. Weike one-step DRI plant with the annual output of 62,000 ton designed by Changsha Metallurgical Design and Research Institute in China started production in 2002, after more than 2 years trial test and technology renovation [29].

The FASTMET process, developed during the early 1990s by Midrex Direct Reduction Corporation to provide a coal-based process for North American locations, is very similar to the rotary hearth pioneered by Inmetco in Ellwood City,

**69**

**Figure 3.**

*Schematic flowsheet of FASTMET process [30].*

*Comprehensive Utilization of Iron-Bearing Converter Wastes*

per year capacity was set up in 1978 at Ellwood City, Pennsylvania.

Pennsylvania for treating waste dusts from steel plants and also a proposed process studied by Salem Furnace Company in Carnegie, Pennsylvania. The nucleus of the FASTMET process originated with the development of the heat fast process in the mid-1960s. The heat fast process consisted of the following steps: (1) mixing and pelletization of iron ore fines and pulverized coal, (2) drying the green pellets on a grate, (3) prereduction on an RHF, and (4) cooling in a shaft furnace. The next step in the evolution of the FASTMET process was the development of the Inmetco process for reduction of stainless steel mill wastes in 1974. The process consisted of the following steps: (1) mixing and pelletization of mill wastes and pulverized coal, (2) prereduction of the green pellets on an RHF, (3) discharge of hot pellets into transfer bins, and (4) charging of hot pellets into a submerged arc furnace. The process was tested in a pilot plant located at Port Colborne, Ontario, and a commercial unit of 60,000 tons

Midrex revived investigations in 1989 and tested a wide range of raw materials in its laboratory in Charlotte, North Carolina. A 2.5 m (8.2 ft) diameter pilot RHF with a capacity of 150 kg/h of reduced iron was installed in 1991 to simulate the reduction portion of the process. This process simulator was utilized to develop data for the design of an industrial unit. Based on the successful laboratory and pilot plant tests, Midrex and its parent company Kobe Steel started construction of an FASTMET demonstration plant in April 1994 at the Kakogawa works of Kobe Steel in Japan. The plant has a production capacity of 2.6 tones/h and was commissioned in September 1995. The demonstration plant is reportedly operating under stable conditions, and several tests have been conducted to develop process parameters for scale-up to a 60 tone/h industrial scale unit. Tests have also been made for producing hot briquetted iron (HBI) and for integrating the FASTMET process with DRI

In the FASTMET process, shown schematically in **Figure 3**, iron ore concentrate,

reductant, and binder are mixed and formed into green pellets that are dried at 120°C and fed to the rotary hearth furnace. The pellets are placed on a solid hearth

As the hearth rotates, the pellets are heated to 1250–1350°C by means of fuel burners firing into the freeboard above the hearth. Reduction to metallic iron is completed in 6–12 min, depending on the materials, temperature, and other

*DOI: http://dx.doi.org/110.5772/intechopen.80329*

melting in an electric arc furnace.

one to two layers deep as shown in **Figure 4** [30–32].

#### *Comprehensive Utilization of Iron-Bearing Converter Wastes DOI: http://dx.doi.org/110.5772/intechopen.80329*

*Recovery and Utilization of Metallurgical Solid Waste*

melt shop too.

**2.2 One-step method**

drum. The material will stay inside for about 25–40 min.

down below 120°C indirectly by spraying water to the outside surface of the cooler

The cooled product is delivered to the product sorting room to screening and classification in order to separate the DRI, magnetic powder, nonmagnetic powder, and return coal fines. The product discharged from the cooler drum is delivered to the screen equipment and separated into two granularities: >4 and <4 mm. To minimize the iron content in nonmagnetic powder, the product of >4 mm will be proceed in three steps in magnetic separator. The magnetic material discharged from the magnetic separator is fed to the steel melt shop. The nonmagnetic material is discharged from the bottom of magnetic separator, regarded as return coal, and delivered to proportioning building. The product of <4 mm is separated in two serial elutriator for pneumatic classification: the light one such as ash is dedusted, and the heavier one is pneumatic delivered to the single magnetic separator. After magnetic classification, the nonmagnetic powder is delivered to nonmagnetic bin by belt conveyor and bucket elevator and then transferred by trucks; the magnetic material will be separated in elutriator, delivered to magnetic bin by belt conveyor and then pressed into block, and finally delivered to the steel

The "one-step" method is mainly composed of concentrate pelletizing—preheating—direct reduction (coal-based kiln reduction/rotary hearth furnace)—cooling. Compared with the traditional two-step method, the preheated pellets with certain intensity are directly delivered to the direct reduction furnace, which not only shortens the process line with satisfactory product quality, but also saves the energy. The key equipment reform and technologies of one-step kiln process are primarily researched and applied into operation in China. Reduction behavior of two kinds of pellets using noncoking coal as reductant is studied and compared. The one is preheated pellet made of magnetite concentrate with composite binder, and the other is fired oxide pellets containing bentonite as binder [15]. Reducibility, compress strength, porosity, and microphases evolution are measured. Results show that preheated pellets possess much better reducibility than fired oxide pellets, which is ascribed to their higher effective diffusivity due to higher porosity. The compressive strength increases obviously after 30 min reduction and achieves a high value at the end of reduction, while the value of metalized pellets from reduction of oxidized pellets is much lower, because of more cracks and fractures formed. Xinjiang magnetite concentrate in China was studied by one-step process for direct reduction. The results show that for Xinjiang magnetite assaying with 69.21% Fe, damp milling and adding agent can improve the quality of green balls obviously. After drying, green balls are preheated at 800°C for 10 min, pellets with compressive strength of 581 N/pellet are achieved, preheated pellets were directly reduced at 1050°C for 80 min, and directly reduced iron assaying 90.33% of total iron and 85.05% of metallic iron and 94.15% of metallization degree are achieved. Compared with the traditional direct reduction of fired oxide pellets in coal-based rotary kilns, one-step process for direct reduction can avoid high-temperature oxidation of pellets at 1150–1300°C, and possess some advantages such as greater economic profit and good quality of direct reduced iron [28]. Weike one-step DRI plant with the annual output of 62,000 ton designed by Changsha Metallurgical Design and Research Institute in China started production in

2002, after more than 2 years trial test and technology renovation [29].

The FASTMET process, developed during the early 1990s by Midrex Direct Reduction Corporation to provide a coal-based process for North American locations, is very similar to the rotary hearth pioneered by Inmetco in Ellwood City,

**68**

Pennsylvania for treating waste dusts from steel plants and also a proposed process studied by Salem Furnace Company in Carnegie, Pennsylvania. The nucleus of the FASTMET process originated with the development of the heat fast process in the mid-1960s. The heat fast process consisted of the following steps: (1) mixing and pelletization of iron ore fines and pulverized coal, (2) drying the green pellets on a grate, (3) prereduction on an RHF, and (4) cooling in a shaft furnace. The next step in the evolution of the FASTMET process was the development of the Inmetco process for reduction of stainless steel mill wastes in 1974. The process consisted of the following steps: (1) mixing and pelletization of mill wastes and pulverized coal, (2) prereduction of the green pellets on an RHF, (3) discharge of hot pellets into transfer bins, and (4) charging of hot pellets into a submerged arc furnace. The process was tested in a pilot plant located at Port Colborne, Ontario, and a commercial unit of 60,000 tons per year capacity was set up in 1978 at Ellwood City, Pennsylvania.

Midrex revived investigations in 1989 and tested a wide range of raw materials in its laboratory in Charlotte, North Carolina. A 2.5 m (8.2 ft) diameter pilot RHF with a capacity of 150 kg/h of reduced iron was installed in 1991 to simulate the reduction portion of the process. This process simulator was utilized to develop data for the design of an industrial unit. Based on the successful laboratory and pilot plant tests, Midrex and its parent company Kobe Steel started construction of an FASTMET demonstration plant in April 1994 at the Kakogawa works of Kobe Steel in Japan. The plant has a production capacity of 2.6 tones/h and was commissioned in September 1995. The demonstration plant is reportedly operating under stable conditions, and several tests have been conducted to develop process parameters for scale-up to a 60 tone/h industrial scale unit. Tests have also been made for producing hot briquetted iron (HBI) and for integrating the FASTMET process with DRI melting in an electric arc furnace.

In the FASTMET process, shown schematically in **Figure 3**, iron ore concentrate, reductant, and binder are mixed and formed into green pellets that are dried at 120°C and fed to the rotary hearth furnace. The pellets are placed on a solid hearth one to two layers deep as shown in **Figure 4** [30–32].

As the hearth rotates, the pellets are heated to 1250–1350°C by means of fuel burners firing into the freeboard above the hearth. Reduction to metallic iron is completed in 6–12 min, depending on the materials, temperature, and other

**Figure 3.** *Schematic flowsheet of FASTMET process [30].*

#### **Figure 4.**

*Cross section and plan view of the rotary hearth furnace [30].*

factors. The DRI is discharged at approximately 1000°C and can be hot charged to an adjacent melter, hot briquetted, or cooled indirectly before storage and/or shipment. The residence time of the pellets in the ?RHF is 12 min. The hot, reduced iron from the RHF is partially cooled to about 1000°C by a water-cooled discharge screw. The product can be obtained either in the form of cold DRI, hot DRI, or HBI. The product can be discharged from the RHF either to a transfer device for conveying the hot DRI directly to an adjacent steelmaking facility, or by gravity to a briquetting system for producing HBI. The off-gas from the RHF flows to a gas handling system, where the SO2, NOx, and particulates can be reduced to the desired limits. The hot off-gas is used for preheating the combustion air for the RHF burners and to supply the heat for drying. The process is designed to recycle all process water. All fines generated in the process are recycled though the feed.

#### **3. Properties of pellets made from BOF wastes**

General metallized pellet production processes are introduced above. In this section, the detailed properties of pellets made from BOF wastes, drying, and reduction behavior will be set forth further.

#### **3.1 Generation and properties of BOF wastes**

Converter sludge is a kind of black slurry with a high water content. It becomes a dense lump after dehydration and then dispersed into fine particles with large specific surface area after dispersion, among which the content of particle with a size below 0.075 mm is larger than 70%, while the percentage below 0.048 mm is larger than 50%. As the dust and mud are so fine that the surface activity is relatively large, it is easy to be absorbed and blown up into the air after drying, which seriously pollutes the surrounding environment. In terms of chemical composition, the total iron content is high and the impurity content is low. Most of them have simple composition, high content of iron ore, and relatively few impurities, which is conducive to comprehensive recovery and utilization. However, a strong alkaline hydroxide would like to be formed after absorbing water because of the contained CaO, MgO, K2O, and Na2O, which may lead to the increase of pH of the water and soil around and is bad for the growth of crops. Hence, reasonable recycling of BOF wastes is very important.

**71**

**Table 3.**

**Table 2.**

*Comprehensive Utilization of Iron-Bearing Converter Wastes*

Chemical composition of the converter sludge obtained from a steelmaking company is shown in **Table 1**. Then, mineralogical phase was analyzed through the Laitz DMRX polarization microscope and the mineralogical content was character-

**Item TFe FeO CaO MgO SiO2 MnO ZnO Al2O3 PbO K2O Na2O** wt, % 54.53 58.54 16.38 5.75 2.31 0.9 0.77 0.74 0.36 0.18 0.1

To investigate the properties of pellets made from BOF sludge, the raw material was dried (at 105°C for 24 h in a drying oven) and finely ground with the size distribution listed in **Table 2**. Then, they were continuously charged into a pelletizing disk to prepare the green pellets. After that, the initial moisture content was obtained through drying method. In total, 100 g of green pellets were weighed and dried in the oven at 200°C for 24 h, and the difference of weights before and after drying was calculated as the moisture content. The compressive strength was measured according to the standard of ISO470016, and the falling strength (drop no.) was counted through repeated pellet falling from a height of 0.5 m to the steel plate with the thickness of 0.01 m until it cracked. In total, 10 balls were measured and the average was taken. The bursting temperature was defined as the maximum temperature at which bursting rate was less than 4%. In total, 50 pellets were placed in a baking cup and heated for 3 min at the predetermined temperature with the flow rate of 1.5 m/s, then moved out, and observed. If two of them were cracked, the relative tempera-

Properties of green pellets were listed in **Table 3**. Moisture content was in the range of 15.29–16.78%, which was much higher compared to ordinary iron ore pellets (about 7–9%) [17, 18], and would make the drying more difficult. Pellets were strong enough with both high compressive strength and falling strength. However, the bursting temperature was low, so the temperature in the primary drying should

**Figure 5** shows optical microstructures of the converter sludge. The major ironbearing phases are magnetite (Fe3O4), iron, and wustite (Fe1 − xO) (**Figure 5a** and **b**). Some of hematite (Fe2O3) (**Figure 5a**) is also observed. Most of the iron-bearing phases are spherical, with the grain size smaller than 50 μm. Gangues observed are mainly composed of silicate crystal phase and glass phase, as shown in **Figure 5b** and **c**, and

**Size, mm >0.5 0.5–0.3 0.3–0.15 0.15–0.105 0.105–0.076 <0.076** wt, % 36.74 8.46 11.24 1.33 14.33 27.90

> **Falling strength (no. of drops/p)**

**Bursting temperature (°C)**

**Compressive strength (N/p)**

Value 15.29–16.78 11.27–16.27 >20 150

*DOI: http://dx.doi.org/110.5772/intechopen.80329*

*Major chemical composition of converter sludge.*

**Table 1.**

ized through X-ray diffraction (XRD) analysis.

ture was recorded as a bursting temperature.

be set as 150°C to avoid great bursting.

*Size distribution of converter sludge after ground.*

**(wt, %)**

*Properties of green pellets made from converter sludge.*

**Item Moisture** 

also coke particles are found in **Figure 5c** and **d**.

**3.2 Properties of pellets prepared from BOF sludge**


#### **Table 1.**

*Recovery and Utilization of Metallurgical Solid Waste*

*Cross section and plan view of the rotary hearth furnace [30].*

factors. The DRI is discharged at approximately 1000°C and can be hot charged to an adjacent melter, hot briquetted, or cooled indirectly before storage and/or shipment. The residence time of the pellets in the ?RHF is 12 min. The hot, reduced iron from the RHF is partially cooled to about 1000°C by a water-cooled discharge screw. The product can be obtained either in the form of cold DRI, hot DRI, or HBI. The product can be discharged from the RHF either to a transfer device for conveying the hot DRI directly to an adjacent steelmaking facility, or by gravity to a briquetting system for producing HBI. The off-gas from the RHF flows to a gas handling system, where the SO2, NOx, and particulates can be reduced to the desired limits. The hot off-gas is used for preheating the combustion air for the RHF burners and to supply the heat for drying. The process is designed to recycle all process

water. All fines generated in the process are recycled though the feed.

General metallized pellet production processes are introduced above. In this section, the detailed properties of pellets made from BOF wastes, drying, and

Converter sludge is a kind of black slurry with a high water content. It becomes a dense lump after dehydration and then dispersed into fine particles with large specific surface area after dispersion, among which the content of particle with a size below 0.075 mm is larger than 70%, while the percentage below 0.048 mm is larger than 50%. As the dust and mud are so fine that the surface activity is relatively large, it is easy to be absorbed and blown up into the air after drying, which seriously pollutes the surrounding environment. In terms of chemical composition, the total iron content is high and the impurity content is low. Most of them have simple composition, high content of iron ore, and relatively few impurities, which is conducive to comprehensive recovery and utilization. However, a strong alkaline hydroxide would like to be formed after absorbing water because of the contained CaO, MgO, K2O, and Na2O, which may lead to the increase of pH of the water and soil around and is bad for the growth of crops. Hence, reasonable recycling of BOF

**3. Properties of pellets made from BOF wastes**

reduction behavior will be set forth further.

**3.1 Generation and properties of BOF wastes**

**70**

**Figure 4.**

wastes is very important.

*Major chemical composition of converter sludge.*

Chemical composition of the converter sludge obtained from a steelmaking company is shown in **Table 1**. Then, mineralogical phase was analyzed through the Laitz DMRX polarization microscope and the mineralogical content was characterized through X-ray diffraction (XRD) analysis.

#### **3.2 Properties of pellets prepared from BOF sludge**

To investigate the properties of pellets made from BOF sludge, the raw material was dried (at 105°C for 24 h in a drying oven) and finely ground with the size distribution listed in **Table 2**. Then, they were continuously charged into a pelletizing disk to prepare the green pellets. After that, the initial moisture content was obtained through drying method. In total, 100 g of green pellets were weighed and dried in the oven at 200°C for 24 h, and the difference of weights before and after drying was calculated as the moisture content. The compressive strength was measured according to the standard of ISO470016, and the falling strength (drop no.) was counted through repeated pellet falling from a height of 0.5 m to the steel plate with the thickness of 0.01 m until it cracked. In total, 10 balls were measured and the average was taken.

The bursting temperature was defined as the maximum temperature at which bursting rate was less than 4%. In total, 50 pellets were placed in a baking cup and heated for 3 min at the predetermined temperature with the flow rate of 1.5 m/s, then moved out, and observed. If two of them were cracked, the relative temperature was recorded as a bursting temperature.

Properties of green pellets were listed in **Table 3**. Moisture content was in the range of 15.29–16.78%, which was much higher compared to ordinary iron ore pellets (about 7–9%) [17, 18], and would make the drying more difficult. Pellets were strong enough with both high compressive strength and falling strength. However, the bursting temperature was low, so the temperature in the primary drying should be set as 150°C to avoid great bursting.

**Figure 5** shows optical microstructures of the converter sludge. The major ironbearing phases are magnetite (Fe3O4), iron, and wustite (Fe1 − xO) (**Figure 5a** and **b**). Some of hematite (Fe2O3) (**Figure 5a**) is also observed. Most of the iron-bearing phases are spherical, with the grain size smaller than 50 μm. Gangues observed are mainly composed of silicate crystal phase and glass phase, as shown in **Figure 5b** and **c**, and also coke particles are found in **Figure 5c** and **d**.


#### **Table 2.**

*Size distribution of converter sludge after ground.*


#### **Table 3.**

*Properties of green pellets made from converter sludge.*

**Figure 5.** *Optical microstructures of the converter sludge.*

**Figure 6.** *XRD analysis of the converter sludge.*

This mineralogical composition of converter sludge is verified through XRD analysis shown in **Figure 6**. The particularly intense peaks of magnetite, iron, and wustite prove that they mainly comprise iron contained phase. The content of hematite is relatively lower. For the slag phases observed above, they are predominantly identified as CaO and CaCO3.

**73**

*Comprehensive Utilization of Iron-Bearing Converter Wastes*

directly increases the risk of bursting during the drying.

**4. Drying mechanism of BOF sludge pellets**

properties [35, 36].

green pellets.

introduction about the experiments.

according to the following equations.

The CaCO3 is formed during the pelletizing with the reaction of formed slaking Ca(OH)2 and CO2 in the air, and two positive charges of Ca2+ will produce strong electrostatic adsorption, which makes the green pellets strong enough [33]. However, so much lime in the sludge also brings the issue of much moisture content in the pellet (~16.52% in average) because of its high hydrophilic ability, which

Green pellets should be dried before being charged into the consequent preheating and reduction process or else they are easily to be cracked or pulverized owing to drastic volatilization of moisture at a high temperature, and this results in the significant drop of the permeability, which will eventually lower the metallization rate of the products in the reduction furnace, or even make the production abnormal. Additionally, it has been reported that about 25% of energy for pellet induration is consumed for drying [12]. Thus, the improvement of the drying performance will be energy efficient. The drying mechanism of iron ore pellets has been studied by several researchers [12, 34–36]. Two-stage drying is assumed for most drying models at first, involving surface evaporation and internal drying after a critical moisture content is reached [12]. Then, four-step drying kinetics of individual pellet is proposed and verified through experimental and numerical research by Tsukerman et al. [34]. Feng et al. investigate effects of some parameters on drying

Further research about drying characteristics of converter sludge pellets was studied to promote its recycle and reutilization [36]. Influence of factors including temperature, time, and flow on their drying properties were studied and optimized through experiments in order to get better reuse of secondary resources through the grate-kiln (or RHF) metalized pellet-producing process. Following is a brief

In an actual production, drying in the traveling grate was divided into two stages [37]. This drying test was performed in the baking cup (with diameter of 80 mm and length of 300 mm) equipped with a crossflow adjusting system to simulate the two-stage thermal condition. The schematic was shown in **Figure 7**. Pellets are divided into three layers and placed in the baking cup (each layer with the height of 60–70 mm, and separated by a meshed stainless steel plate). Afterward, they were quickly covered by the burner and dried according to the scheduled time, flow, and temperature. Finally, they were moved out and cooled naturally. The bursting pellets for each layer were collected and weighed, respectively, and the remaining moisture was measured using the same method as the

An orthogonal array was applied in this drying test. Four technical parameters were selected based on operation experience in pelletizing plant: first drying stage time (t1: 5, 7, 9 min), the second drying temperature (T2: 200, 300, 400°C), second drying time (t2: 2, 4, 6 min), and second drying flow rate (v2: 1.0, 1.4, 1.8 m/s, standard state), respectively. The temperature and flow rate in the first drying stage were set as fixed factors (T1 = 150°C; v1 = 1.5 m/s) according to the previous bursting temperature measurement. Bursting rate of pellets and the dehydration rate were considered as two major indicators of drying characteristics and calculated

Busting rate (%) = m1/m0 × 100 (1)

*DOI: http://dx.doi.org/110.5772/intechopen.80329*

*Recovery and Utilization of Metallurgical Solid Waste*

**72**

**Figure 6.**

**Figure 5.**

*Optical microstructures of the converter sludge.*

nantly identified as CaO and CaCO3.

*XRD analysis of the converter sludge.*

This mineralogical composition of converter sludge is verified through XRD analysis shown in **Figure 6**. The particularly intense peaks of magnetite, iron, and wustite prove that they mainly comprise iron contained phase. The content of hematite is relatively lower. For the slag phases observed above, they are predomi-

The CaCO3 is formed during the pelletizing with the reaction of formed slaking Ca(OH)2 and CO2 in the air, and two positive charges of Ca2+ will produce strong electrostatic adsorption, which makes the green pellets strong enough [33]. However, so much lime in the sludge also brings the issue of much moisture content in the pellet (~16.52% in average) because of its high hydrophilic ability, which directly increases the risk of bursting during the drying.

## **4. Drying mechanism of BOF sludge pellets**

Green pellets should be dried before being charged into the consequent preheating and reduction process or else they are easily to be cracked or pulverized owing to drastic volatilization of moisture at a high temperature, and this results in the significant drop of the permeability, which will eventually lower the metallization rate of the products in the reduction furnace, or even make the production abnormal. Additionally, it has been reported that about 25% of energy for pellet induration is consumed for drying [12]. Thus, the improvement of the drying performance will be energy efficient. The drying mechanism of iron ore pellets has been studied by several researchers [12, 34–36]. Two-stage drying is assumed for most drying models at first, involving surface evaporation and internal drying after a critical moisture content is reached [12]. Then, four-step drying kinetics of individual pellet is proposed and verified through experimental and numerical research by Tsukerman et al. [34]. Feng et al. investigate effects of some parameters on drying properties [35, 36].

Further research about drying characteristics of converter sludge pellets was studied to promote its recycle and reutilization [36]. Influence of factors including temperature, time, and flow on their drying properties were studied and optimized through experiments in order to get better reuse of secondary resources through the grate-kiln (or RHF) metalized pellet-producing process. Following is a brief introduction about the experiments.

In an actual production, drying in the traveling grate was divided into two stages [37]. This drying test was performed in the baking cup (with diameter of 80 mm and length of 300 mm) equipped with a crossflow adjusting system to simulate the two-stage thermal condition. The schematic was shown in **Figure 7**. Pellets are divided into three layers and placed in the baking cup (each layer with the height of 60–70 mm, and separated by a meshed stainless steel plate). Afterward, they were quickly covered by the burner and dried according to the scheduled time, flow, and temperature. Finally, they were moved out and cooled naturally. The bursting pellets for each layer were collected and weighed, respectively, and the remaining moisture was measured using the same method as the green pellets.

An orthogonal array was applied in this drying test. Four technical parameters were selected based on operation experience in pelletizing plant: first drying stage time (t1: 5, 7, 9 min), the second drying temperature (T2: 200, 300, 400°C), second drying time (t2: 2, 4, 6 min), and second drying flow rate (v2: 1.0, 1.4, 1.8 m/s, standard state), respectively. The temperature and flow rate in the first drying stage were set as fixed factors (T1 = 150°C; v1 = 1.5 m/s) according to the previous bursting temperature measurement. Bursting rate of pellets and the dehydration rate were considered as two major indicators of drying characteristics and calculated according to the following equations.

$$\text{Dehydration rate (\%)} \ = \ (\text{m}\_2 \text{ - m}\_3)/\text{m}\_2 \times 100 \tag{2}$$

where, m1 is the weight of bursting pellets, m0 is the weight of total pellets, m2 is the weight of water in green pellets, and m3 is the weight of water in dried pellets.

**Figure 7.**

*Schematic of the drying simulator.*

**75**

ture and flow rate.

**Figure 9.**

*Dehydration rate of dried pellets.*

19.16%, respectively.

the differential pressure of vapor.

**5. Reduction mechanism of BOF sludge pellets**

*Comprehensive Utilization of Iron-Bearing Converter Wastes*

**Figure 8** shows the bursting rate of pellets in each layer for the nine tests. High bursting rate means poor drying performance. It is found that bursting rate of the upper pellets in nos. 3, 6, and 2 is the worst, with the values of 46.41, 32.47, and 23.12%, respectively. Common conditions they share are short drying time (5–7 min) in first drying section, high level of temperature (300–400°C), and fast flow rate (1.4–1.8 m/s) in second drying section. It can be speculated that if the first drying time is not long enough, cracking rate of pellets will go up during the second drying section caused by the excessive expansion force generated through rapid and intense vaporization of residual moisture in the interior of pellet at high tempera-

**Figure 9** shows the dehydration rate of pellets in each layer. Obviously, the bottom pellets have the lower dehydration percentage compared with the upper and middle one, the lowest value of which are nos.1, 2, and 6, with 15.58, 32.31, and

Actually, moisture evaporation is a dynamic balance of liquid water gasification and vapor condensation, and evaporation rate is the difference of these two reactions [25]. It follows that the moisture evaporation velocity depends on the temperature and the pressure difference between saturated and ambient vapor. The higher the temperature and pressure difference, the faster is the evaporation rate. So, this is the reason why the dehydration rate in the bottom level is the lowest. For one thing, the temperature at the bottom is lower than the upper one as the endothermic evaporation reaction takes place when gas flows from up to down. For another, the vapor generated in the upper gradually enters into the main flow, which will lower

Most DRI production is melted in electric arc furnaces for steelmaking. Minor

amounts may be charged into the ironmaking blast furnace. So the reduction degree, compressive strength, and dezincification rate are considered as three important indicators. They were energetically investigated by metallurgical researchers recently. The study of reduction behavior of the composite briquettes shows that both the metallization and dezincification ratios increased with the increasing temperature and the time, but first increased and then decreased with

*DOI: http://dx.doi.org/110.5772/intechopen.80329*

**Figure 8.** *Bursting rate of dried pellets.*

*Comprehensive Utilization of Iron-Bearing Converter Wastes DOI: http://dx.doi.org/110.5772/intechopen.80329*

**Figure 9.** *Dehydration rate of dried pellets.*

*Recovery and Utilization of Metallurgical Solid Waste*

Dehydration rate (%) = (m2 − m3)/m2 × 100 (2)

where, m1 is the weight of bursting pellets, m0 is the weight of total pellets, m2 is the weight of water in green pellets, and m3 is the weight of water in dried pellets.

**74**

**Figure 8.**

*Bursting rate of dried pellets.*

**Figure 7.**

*Schematic of the drying simulator.*

**Figure 8** shows the bursting rate of pellets in each layer for the nine tests. High bursting rate means poor drying performance. It is found that bursting rate of the upper pellets in nos. 3, 6, and 2 is the worst, with the values of 46.41, 32.47, and 23.12%, respectively. Common conditions they share are short drying time (5–7 min) in first drying section, high level of temperature (300–400°C), and fast flow rate (1.4–1.8 m/s) in second drying section. It can be speculated that if the first drying time is not long enough, cracking rate of pellets will go up during the second drying section caused by the excessive expansion force generated through rapid and intense vaporization of residual moisture in the interior of pellet at high temperature and flow rate.

**Figure 9** shows the dehydration rate of pellets in each layer. Obviously, the bottom pellets have the lower dehydration percentage compared with the upper and middle one, the lowest value of which are nos.1, 2, and 6, with 15.58, 32.31, and 19.16%, respectively.

Actually, moisture evaporation is a dynamic balance of liquid water gasification and vapor condensation, and evaporation rate is the difference of these two reactions [25]. It follows that the moisture evaporation velocity depends on the temperature and the pressure difference between saturated and ambient vapor. The higher the temperature and pressure difference, the faster is the evaporation rate. So, this is the reason why the dehydration rate in the bottom level is the lowest. For one thing, the temperature at the bottom is lower than the upper one as the endothermic evaporation reaction takes place when gas flows from up to down. For another, the vapor generated in the upper gradually enters into the main flow, which will lower the differential pressure of vapor.

#### **5. Reduction mechanism of BOF sludge pellets**

Most DRI production is melted in electric arc furnaces for steelmaking. Minor amounts may be charged into the ironmaking blast furnace. So the reduction degree, compressive strength, and dezincification rate are considered as three important indicators. They were energetically investigated by metallurgical researchers recently. The study of reduction behavior of the composite briquettes shows that both the metallization and dezincification ratios increased with the increasing temperature and the time, but first increased and then decreased with

the increasing C/O molar ratio [9]. The strength of the metallized pellet could be controlled by reduction temperature, sintering time, additive quality/quantity, and manner of reduction [22]. DRI strength values are found to decrease from 200 to 30 kg during reduction and then strengthened up to 50 kg as a result of sintering and fusion [23].

In order to clarify reduction mechanism of BOF sludge pellets, experiments to simulate the grate-kiln metalizing process is conducted. Flow diagram is shown in **Figure 10**, including converter sludge pellets preparing, drying, preheating in the baking cup, and subsequent direct reduction in the preheated pellets with reductant of coal in the simulated rotary kiln.

Experimental materials include the iron-bearing converter sludge and coal. Converter sludge's chemical composition and mineralogical phase are shown above. It mainly contains 54.53% TFe, 16.38% CaO, and 0.77% ZnO (weight percentage). The major iron-bearing phases are magnetite (Fe3O4), iron, and wustite (Fe1 − xO). Chemical analysis of coal as the reductant and its softening and melting

#### **Figure 10.**

*Flow diagram of direct reduction experiment.*


*ad = on air dry basis, daf = on dry ash free, FC = fixed carbon, M = moisture, A = ash, and V = volatile.*

#### **Table 4.**

*Chemical analysis of coal.*


**77**

**Figure 11.**

*Schematic of the metalizing simulator.*

*Comprehensive Utilization of Iron-Bearing Converter Wastes*

properties are shown in **Tables 4** and **5**, indicating it is suitable for direct reduction

The simulated rotary kiln is shown in **Figure 11**. It mainly consisted of a rotary drum (with a diameter of 130 mm and a length of 200 mm, made of heat-resistant

About 500 g of preheated pellets and coal at different ratio (C/O molar ratio) were put into the steel drum, which had been heated up to the target temperature in the furnace. Afterward, the direct reduction is proceeded for the predetermined residence time in the drum with a rotation speed of 30 rpm. Finally, they were moved out and cooled down to the ambient temperature. Optical microstructures of metallized pellets were analyzed through microscope. The compressive strengths before and after reduction were measured. Metallization rate was calculated on

Metallization rate (%) = MFe(%)/TFe(%) × 100 (3)

Nine tests were conducted, and three technical parameters including temperature (1000, 1050, and 1100°C), time (1.5, 2.0, 2.5 h), and coal ratio (C/O molar ratio, 1.1, 1.3, and 1.5) were selected. Results show that the nos. 3 (T = 1050°C; t = 2.5 h; C/O = 1.5), 2 (T = 1050°C; t = 2 h; C/O = 1.3), and 6 tests (T = 1100°C; t = 2.5 h; C/O = 1.1) have the highest metallization rate of 74.7, 47.7, 45.7%, respectively. Common conditions they share are relatively long reaction time and high reduction temperature. Their corresponding compressive strengths are 1014, 897.4 and 1506.7 N/p, indicating pellets produced from certain tests meet the strength requirement of material served for BF. In addition, the residual zinc contents of these three reduced pellets are 0.44, 0.54, and 0.38%, and the average dezincification rate is calculated as 41.6%. This index can be further improved in an actual rotary kiln because the vapor of zinc produced during reduction could be brought

*DOI: http://dx.doi.org/110.5772/intechopen.80329*

steel) and an electrically heated tube furnace.

basis of chemical analysis according to the following equations.

where, MFe means metallic iron, and TFe means total iron.

with high ash melting point.

out with the flow.

#### **Table 5.**

*Softening and melting properties of coal.*

*Recovery and Utilization of Metallurgical Solid Waste*

of coal in the simulated rotary kiln.

and fusion [23].

the increasing C/O molar ratio [9]. The strength of the metallized pellet could be controlled by reduction temperature, sintering time, additive quality/quantity, and manner of reduction [22]. DRI strength values are found to decrease from 200 to 30 kg during reduction and then strengthened up to 50 kg as a result of sintering

In order to clarify reduction mechanism of BOF sludge pellets, experiments to simulate the grate-kiln metalizing process is conducted. Flow diagram is shown in **Figure 10**, including converter sludge pellets preparing, drying, preheating in the baking cup, and subsequent direct reduction in the preheated pellets with reductant

Experimental materials include the iron-bearing converter sludge and coal. Converter sludge's chemical composition and mineralogical phase are shown above. It mainly contains 54.53% TFe, 16.38% CaO, and 0.77% ZnO (weight percentage). The major iron-bearing phases are magnetite (Fe3O4), iron, and wustite (Fe1 − xO). Chemical analysis of coal as the reductant and its softening and melting

**Composition FC, ad M, ad A, ad V, ad V, daf** wt, % 76.18 0.72 9.68 13.42 14.98

*ad = on air dry basis, daf = on dry ash free, FC = fixed carbon, M = moisture, A = ash, and V = volatile.*

**Softening temperature**

1125 1180 1210 1280

**Half global temperature**

**Flowing temperature**

**76**

**Table 5.**

**Table 4.**

Value, °C

**Figure 10.**

*Chemical analysis of coal.*

**Item Distortional** 

*Softening and melting properties of coal.*

**temperature**

*Flow diagram of direct reduction experiment.*

properties are shown in **Tables 4** and **5**, indicating it is suitable for direct reduction with high ash melting point.

The simulated rotary kiln is shown in **Figure 11**. It mainly consisted of a rotary drum (with a diameter of 130 mm and a length of 200 mm, made of heat-resistant steel) and an electrically heated tube furnace.

About 500 g of preheated pellets and coal at different ratio (C/O molar ratio) were put into the steel drum, which had been heated up to the target temperature in the furnace. Afterward, the direct reduction is proceeded for the predetermined residence time in the drum with a rotation speed of 30 rpm. Finally, they were moved out and cooled down to the ambient temperature. Optical microstructures of metallized pellets were analyzed through microscope. The compressive strengths before and after reduction were measured. Metallization rate was calculated on basis of chemical analysis according to the following equations.

Metallization rate (%) = MFe(%)/TFe(%) × 100 (3)

where, MFe means metallic iron, and TFe means total iron.

Nine tests were conducted, and three technical parameters including temperature (1000, 1050, and 1100°C), time (1.5, 2.0, 2.5 h), and coal ratio (C/O molar ratio, 1.1, 1.3, and 1.5) were selected. Results show that the nos. 3 (T = 1050°C; t = 2.5 h; C/O = 1.5), 2 (T = 1050°C; t = 2 h; C/O = 1.3), and 6 tests (T = 1100°C; t = 2.5 h; C/O = 1.1) have the highest metallization rate of 74.7, 47.7, 45.7%, respectively. Common conditions they share are relatively long reaction time and high reduction temperature. Their corresponding compressive strengths are 1014, 897.4 and 1506.7 N/p, indicating pellets produced from certain tests meet the strength requirement of material served for BF. In addition, the residual zinc contents of these three reduced pellets are 0.44, 0.54, and 0.38%, and the average dezincification rate is calculated as 41.6%. This index can be further improved in an actual rotary kiln because the vapor of zinc produced during reduction could be brought out with the flow.

**Figure 11.** *Schematic of the metalizing simulator.*

#### **Figure 12.**

*Optical reflecting microstructures of the reduced pellets, 200×: (a) and (b) interior and (c) and (d) exterior. L: silicate, SFCA: composite calcium ferrite, Fe: metallic iron, and FexO: wustite.*

**Figure 12** shows optical microstructures of the reduced pellets. A lot of wustite exists in the interior of metalized pellets as shown in **Figure 12a** and **b**, while a large amount of metallic iron, which looks much whiter and brighter than wustite, is mainly observed in the exterior shown in **Figure 12c** and **d**. It can be deduced that the reduction condition in the out part of pellets is much better than the interior at the beginning, and the compact shell of iron rapidly formed in the initial makes the diffusion of reduction gas more difficult from outside to the inner.

#### **6. Conclusions**

Converter sludge is a kind of useful secondary resource rich in valuable iron and calcium oxide. High initial moisture in converter sludge enhanced the bursting risk during drying and made this process difficult. The upper layer bursting rate and the bottom layer dehydration rate are considered as main indicators of drying performance. Technical factors of temperature and retention time in the drying section have remarkable influence on the drying performance, which should be paid close attention in future.

Two-step and one-step coal-based methods have been extensively researched recently and adopted into operation of the BOF wastes recycling. Effects of direct reduction parameters including temperature, time, and coal ratio on the metallization rate and compressive strength are also studied. Results show that reduction time and temperature have remarkable influence on the metallization rate. The

**79**

provided the original work is properly cited.

Technology Beijing, Beijing, P. R. China

\*Address all correspondence to: longhu042@126.com

*Comprehensive Utilization of Iron-Bearing Converter Wastes*

indexes of metallization rate and compressive strength of metallized pellets reduced from the BOF sludge can satisfy the requirement of iron burden for BF. To improve the efficiency, the gas-based direct reduction especially hydrogen as the reductants may be considered to develop breakthrough technologies for emission reduction.

The financial support from Natural Science Foundation of Hebei Province in China (No. E2017203157) and China Postdoctoral Science Foundation is gratefully acknowledged. The authors also thank Professor Yanzhong Jia and Delan Liang

Mutual development of metallurgical technology and ecological environment is

, Ming-Hua Bai3

1 School of Mechanical and Automotive Engineering, South China University of

3 National Engineering Research Center for Equipment and Technology of Cold

4 School of Metallurgical and Ecological Engineering, University of Science and

2 Baowu Group Guangdong Shaoguan Iron and Steel Co., Ltd., Shaoguan,

Strip Rolling, Yanshan University, Qinhuangdao, Hebei, P. R. China

, Yanzhong Jia4

and

(University of Science and Technology Beijing) for their supports.

*DOI: http://dx.doi.org/110.5772/intechopen.80329*

**Acknowledgements**

**Conflict of interest**

**Other declarations**

our persistent pursuit.

**Author details**

Wensheng Qiu<sup>2</sup>

Guangdong, P. R. China

\*, Dong Liu2

, Lie-Jun Li1

Technology, Guangzhou, Guangdong, P. R. China

Hu Long1

There is no conflict of interest.

© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

*Comprehensive Utilization of Iron-Bearing Converter Wastes DOI: http://dx.doi.org/110.5772/intechopen.80329*

indexes of metallization rate and compressive strength of metallized pellets reduced from the BOF sludge can satisfy the requirement of iron burden for BF. To improve the efficiency, the gas-based direct reduction especially hydrogen as the reductants may be considered to develop breakthrough technologies for emission reduction.

### **Acknowledgements**

*Recovery and Utilization of Metallurgical Solid Waste*

**Figure 12** shows optical microstructures of the reduced pellets. A lot of wustite exists in the interior of metalized pellets as shown in **Figure 12a** and **b**, while a large amount of metallic iron, which looks much whiter and brighter than wustite, is mainly observed in the exterior shown in **Figure 12c** and **d**. It can be deduced that the reduction condition in the out part of pellets is much better than the interior at the beginning, and the compact shell of iron rapidly formed in the initial makes the diffusion of reduction gas more difficult from outside to the

*L: silicate, SFCA: composite calcium ferrite, Fe: metallic iron, and FexO: wustite.*

*Optical reflecting microstructures of the reduced pellets, 200×: (a) and (b) interior and (c) and (d) exterior.* 

Converter sludge is a kind of useful secondary resource rich in valuable iron and calcium oxide. High initial moisture in converter sludge enhanced the bursting risk during drying and made this process difficult. The upper layer bursting rate and the bottom layer dehydration rate are considered as main indicators of drying performance. Technical factors of temperature and retention time in the drying section have remarkable influence on the drying performance, which should be paid close attention in future. Two-step and one-step coal-based methods have been extensively researched recently and adopted into operation of the BOF wastes recycling. Effects of direct reduction parameters including temperature, time, and coal ratio on the metallization rate and compressive strength are also studied. Results show that reduction time and temperature have remarkable influence on the metallization rate. The

**78**

inner.

**Figure 12.**

**6. Conclusions**

The financial support from Natural Science Foundation of Hebei Province in China (No. E2017203157) and China Postdoctoral Science Foundation is gratefully acknowledged. The authors also thank Professor Yanzhong Jia and Delan Liang (University of Science and Technology Beijing) for their supports.

## **Conflict of interest**

There is no conflict of interest.

## **Other declarations**

Mutual development of metallurgical technology and ecological environment is our persistent pursuit.

## **Author details**

Hu Long1 \*, Dong Liu2 , Lie-Jun Li1 , Ming-Hua Bai3 , Yanzhong Jia4 and Wensheng Qiu<sup>2</sup>

1 School of Mechanical and Automotive Engineering, South China University of Technology, Guangzhou, Guangdong, P. R. China

2 Baowu Group Guangdong Shaoguan Iron and Steel Co., Ltd., Shaoguan, Guangdong, P. R. China

3 National Engineering Research Center for Equipment and Technology of Cold Strip Rolling, Yanshan University, Qinhuangdao, Hebei, P. R. China

4 School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, Beijing, P. R. China

\*Address all correspondence to: longhu042@126.com

© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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*Recovery and Utilization of Metallurgical Solid Waste*

reduction of BOF-powders to direct reduced iron (DRI) production. Process Safety and Environmental Protection.

[9] Xia LG, Mao R, Zhang JL, Xu XN, Wei MF, Yang FH. Reduction process and zinc removal from composite briquettes composed of dust and sludge from a steel enterprise. International Journal of Minerals, Metallurgy, and Materials. 2015;**22**(2):122-131

[10] Su FW, Lampinen HO, Robinson R. Recycling of sludge and dust to the BOF converter by cold bonded pelletizing. ISIJ International.

[11] Prieto Martinez N, Herrera Trejo M, Morales Estrella R, et al. Induration process of pellets prepared from mixed magnetite–35% hematite concentrates. ISIJ International. 2014;**54**(3):605-612

[12] Patisson F, Bellot JP, Ablitzer D. Study of moisture transfer during the strand sintering process. Metallurgical Transactions B. 1990;**21**(1):37-47

[13] Aota J, Morin L, Zhuang Q , Clements B. Direct reduced iron production using cold bonded carbon bearing pellets part l—Laboratory metallization. Ironmaking and Steelmaking. 2006;**33**(5):426-428

[14] Zhuang Q , Clements B, Aota J, Morin L. DRI production using cold bonded carbon bearing pellets part 2—Rotary kiln process modelling. Ironmaking and Steelmaking.

[15] Zhu DQ, Mendes V, Chun TJ, Pan J, Li QH, Li J, et al. Direct reduction behaviors of composite binder magnetite pellets in coal-based graterotary kiln process. ISIJ International.

2006;**33**(5):429-432

2011;**51**(2):214-219

2016;**102**:410-420

2004;**44**(4):770-776

[1] Cristina N, Lobato C, Villegas EA, Mansur MB. Management of solid wastes from steelmaking and

galvanizing processes: A brief review. Resources, Conservation and Recycling.

[2] She XF, Xue QG, Dong JJ, Wang JS, Zeng H, Li HF, et al. Study on basic properties of typical industrial dust from iron and steel plant and analysis of its utilization. The Chinese Journal of Process Engineering. 2009;**9**:7-12 (in

[3] Zhang YB, Liu BB, Xiong L, Li GH, Jiang T. Recycling of carbonaceous ironbearing dusts from iron & steel plants by composite agglomeration process (CAP). Ironmaking and Steelmaking.

[4] Das B, Prakash S, Reddy PSR, Misra VN. An overview of utilization of slag and sludge from steel industries. Resources, Conservation and Recycling.

[5] López FA, Balcázar N, Formoso A, Pinto M, Rodriguez M. The recycling of Linz-Donawitz (LD) converter slag by use as a liming agent on pasture land. Waste Management and Research.

[6] Makkonen HT, Heino J, Laitila L, et al. Optimisation of steel plant recycling in Finland: Dusts, scales and sludge. Resources, Conservation and Recycling. 2002;**35**(1-2):77-84

[7] Besta P, Samolejová A, Janovská K, Lenort R, Haverland J. Utjecaj štetnih elemenata pri proizvodnji sirovog željeza u odnosu na ulaznu i izlaznu materijalnu bilancu. Metalurgija.

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2012;**51**(3):325-328

**80**

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[19] Sun K, Lu WK. Atheoretical investigation of kinetics and mechanisms of ironore reduction in an ore/coal composite. ISIJ International. 1999;**39**(2):123-129

[20] Nascimento RC, Mouräo MB, Capocchi JDH. Kinetics and catastrophic swelling during reduction of iron ore in carbon bearing pellets. Ironmaking and Steelmaking. 1999;**26**(3):182-186

[21] Sharma MK, Solanki V, Roy GG, Sen PK. Study of reduction behaviour of prefabricated iron ore–graphite/ coal composite pellets in rotary hearth furnace. Ironmaking and Steelmaking. 2013;**40**(8):590-597

[22] Gupta RC, Gautam JP. The effect of additives and reductants on the strength of reduced iron ore pellet. ISIJ International. 2003; **43**(12):1913-1918

[23] Tsujihata K, Mitoma I, Fukagawa Y, Hashimoto S, Toda H. Apparatus for operating a shaft furnace by detecting the falling speed of the charge. Transactions of the Iron and Steel Institute of Japan. US3581070[P]. 1971.

[24] Long H, Bai MH, Jia YZ, Liang DL, Ren SB. Investigation of factors affecting drying characteristics of pellets made from iron-bearing converter sludge. Ironmaking and Steelmaking. 2016;**43**(3):1-7. DOI: 10.1080/03019233.2016.1269039

[25] Long H, Jia YZ, Liang DL, et al. Effect of parameters on reduction behaviour of preheated converter sludge pellets in grate-rotary kiln process. Ironmaking & Steelmaking. 2017;**3**:1-6

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[31] Miyagawa K, Meissner DC. Development of the FASTMET as a new direct reduction process. In: 1998 ISS Ironmaking Conference Proceedings. Vol. 57. 1998. pp. 877-881

[32] Lehmkuler HJ, Hofmann W, Fontana P, De Marchi G. INMETCO process: An attractive solution for

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**83**

Section 4

Comprehensive Utilization

of Red Mud

Section 4
