*2.2.2. Sludge*

As a result of the gas treatment, sludge from wet dedusting systems, which have a high iron content with the order of 75 to 80%, is obtained from the implantation of the dedusting systems in the steelworks. Companies that have not developed ways to recycle this waste end up destining them to the landfills, excessively increasing the cost of production, since its volume generation is considerable, reaching values of the order of 36 kg.t−1 of steel produced. One of the main problems for the recycling of steel slurry in the steelmaking process itself is its high moisture content [3].

up to 20 wt.% of fine steel sludge generated at an integrated siderurgic plant on the properties of a kaolinitic clay-based ceramic used to the produce bricks and tiles. Other authors [17] also focused on evaluating the microstructure and the inertization of potentially toxic elements through ceramic matrix by performing solution and leaching test in the ceramics with residue

1.86 0.12 74.03 0.90 16.50 3.42 0.16 0.33 2.78 —

**O Na2**

**O ZnO LoI\***

33

Recycling of Steelmaking Plant Wastes in Clay Bricks http://dx.doi.org/10.5772/intechopen.74431

**O3 Fetotal TiO2 CaO MgO K2**

**Figure 8** shows the fracture surface micrographs of the ceramic with 5% of waste incorporated. A very rough microstructure is observed with the presence of well-distributed porous particles. These particles are associated with fine steel sludge and are not adhered to the ceramic matrix. This may lead to a reduction in the mechanical strength of products incorpo-

**Figure 9** shows the fracture surface micrographs of the clay with 20% of waste incorporated. It is possible to observe that the steel sludge is relatively well distributed in the clay matrix. However, with the increase of its quantity, more regions appear with fails. In addition, increasing the waste amount, which exhibits an inert behavior during firing, reduces the amount of

In **Table 3** the leaching and solubilization results are presented, indicating the values obtained and the acceptable limit, according to the Brazilian legislation of potentially toxic metals of the formulation containing 5% of steel sludge. It is possible to observe that in the leached standard parameters, Ba, Cd, Cr, and Pb are present in quantities well below the limit values. Already solubilized, Al is present in a quantity nine times higher than the limit acceptable by norm. Al present in clay is one of its natural constituents and therefore apparently lies in equilibrium in nature. In this way its content above the stipulated limit by norm is questionable from the point of view of environmental problems. Other elements such as Cd, Cu, Fe, Mn, and Pb are in very small concentrations, being below the detection limit of the equipment.

To evaluate the effect of steel sludge incorporation on the properties of ceramics for civil construction, Vieira et al. [15] prepared specimens with additions of 0, 5, 10, and 20 wt.% of fine

It can be seen in **Figure 10** the dried bulk density and the sintered bulk density of the formulations. One should notice that steel sludge waste (SSW) additions tend to increase the dried bulk density, mainly for the 20 wt.% addition. This behavior is probably due to the higher real density of the SSW particles compared with the clay particles and also the coarser particles of

In **Figure 11**, the results of the analyzed properties of the sintered ceramics as function of residue incorporation are represented. An interesting result can be noted for water absorption;

the SSW as compared with the clay, which may favor the packaging.

clay, the main material responsible for the consolidation of the ceramic particles.

incorporation sintered at 900°C.

**Table 2.** Steel sludge chemical composition (wt.%) [15].

**SiO2 Al2**

Loss on ignition.

\*

rating higher residue content.

steel sludge into a kaolinitic clay from Brazil.

According to **Figure 7**, the steel sludge has a particle size distribution that the equivalent spherical diameter varies from 1 to 800 μm and mean particle sizes with 35.6 μm. For reddish ceramic production, this is an appropriate characteristic, in which these industries use materials with particles having sizes lower than 2000 μm.

In relation to the chemical composition (**Table 2**), the steel sludge is composed mainly by Fe, with 74.03%. The CaO comes from calcite introduced in the process to convert pig iron into steel. The small MgO content is associated with the desulfurizing agent also used in the steel process, which also contributes with CaO. The content of SiO2 can be derived from the oxidation of silicon present in pig iron, while the ZnO content is associated with the use of galvanized scrap.

The influence of steel sludge incorporation into clayey ceramic products was evaluated by Vieira et al. (2007) [16]. In this paper, the authors evaluated the influence of incorporation of

**Figure 7.** Steel sludge particle size distribution [15].


**Table 2.** Steel sludge chemical composition (wt.%) [15].

In this context, it is possible to predict that the SS particles do not react with the clay compounds. The insufficient level of chemical bonding leads the SS particles to stay loose from

As a result of the gas treatment, sludge from wet dedusting systems, which have a high iron content with the order of 75 to 80%, is obtained from the implantation of the dedusting systems in the steelworks. Companies that have not developed ways to recycle this waste end up destining them to the landfills, excessively increasing the cost of production, since its volume generation is considerable, reaching values of the order of 36 kg.t−1 of steel produced. One of the main problems for the recycling of steel slurry in the steelmaking process itself is its high moisture content [3].

According to **Figure 7**, the steel sludge has a particle size distribution that the equivalent spherical diameter varies from 1 to 800 μm and mean particle sizes with 35.6 μm. For reddish ceramic production, this is an appropriate characteristic, in which these industries use materi-

In relation to the chemical composition (**Table 2**), the steel sludge is composed mainly by Fe, with 74.03%. The CaO comes from calcite introduced in the process to convert pig iron into steel. The small MgO content is associated with the desulfurizing agent also used in the steel process,

con present in pig iron, while the ZnO content is associated with the use of galvanized scrap.

The influence of steel sludge incorporation into clayey ceramic products was evaluated by Vieira et al. (2007) [16]. In this paper, the authors evaluated the influence of incorporation of

can be derived from the oxidation of sili-

matrix and therefore generates defects such as voids and cracks in the product.

als with particles having sizes lower than 2000 μm.

32 Current Topics in the Utilization of Clay in Industrial and Medical Applications

which also contributes with CaO. The content of SiO2

**Figure 7.** Steel sludge particle size distribution [15].

*2.2.2. Sludge*

up to 20 wt.% of fine steel sludge generated at an integrated siderurgic plant on the properties of a kaolinitic clay-based ceramic used to the produce bricks and tiles. Other authors [17] also focused on evaluating the microstructure and the inertization of potentially toxic elements through ceramic matrix by performing solution and leaching test in the ceramics with residue incorporation sintered at 900°C.

**Figure 8** shows the fracture surface micrographs of the ceramic with 5% of waste incorporated. A very rough microstructure is observed with the presence of well-distributed porous particles. These particles are associated with fine steel sludge and are not adhered to the ceramic matrix. This may lead to a reduction in the mechanical strength of products incorporating higher residue content.

**Figure 9** shows the fracture surface micrographs of the clay with 20% of waste incorporated. It is possible to observe that the steel sludge is relatively well distributed in the clay matrix. However, with the increase of its quantity, more regions appear with fails. In addition, increasing the waste amount, which exhibits an inert behavior during firing, reduces the amount of clay, the main material responsible for the consolidation of the ceramic particles.

In **Table 3** the leaching and solubilization results are presented, indicating the values obtained and the acceptable limit, according to the Brazilian legislation of potentially toxic metals of the formulation containing 5% of steel sludge. It is possible to observe that in the leached standard parameters, Ba, Cd, Cr, and Pb are present in quantities well below the limit values. Already solubilized, Al is present in a quantity nine times higher than the limit acceptable by norm. Al present in clay is one of its natural constituents and therefore apparently lies in equilibrium in nature. In this way its content above the stipulated limit by norm is questionable from the point of view of environmental problems. Other elements such as Cd, Cu, Fe, Mn, and Pb are in very small concentrations, being below the detection limit of the equipment.

To evaluate the effect of steel sludge incorporation on the properties of ceramics for civil construction, Vieira et al. [15] prepared specimens with additions of 0, 5, 10, and 20 wt.% of fine steel sludge into a kaolinitic clay from Brazil.

It can be seen in **Figure 10** the dried bulk density and the sintered bulk density of the formulations. One should notice that steel sludge waste (SSW) additions tend to increase the dried bulk density, mainly for the 20 wt.% addition. This behavior is probably due to the higher real density of the SSW particles compared with the clay particles and also the coarser particles of the SSW as compared with the clay, which may favor the packaging.

In **Figure 11**, the results of the analyzed properties of the sintered ceramics as function of residue incorporation are represented. An interesting result can be noted for water absorption;

**Figure 8.** Micrograph obtained by SEM of the ceramic incorporated with 5% of steel sludge and sintered at 900° C in magnification of 800× [17].

**Figure 9.** Micrograph obtained by SEM of the ceramic incorporated with 20% of steel sludge and sintered at 900° C in magnification of 500× (a) and 1000× (b) [17].

considering the error bars, this property is little affected by the residue amount increasing. Therefore, as the open porosity of the ceramics containing residue is practically unchanged, it is correct to affirm that the partial substitution of the clay by the residue aided in the reduction of the loss on ignition. It is known that the loss on fire caused by clay is due to dehydroxylation of kaolinite to form metakaolinite; in this way, this mechanism is responsible for leaving porosity in the ceramic. When the clay is replaced by the residue, although it is reducing the content of clay minerals which are the most reactive particles and contribute most to the consolidation mechanisms during the sintering, it is also reducing the loss to fire; for this reason, this property is little changed.

This same explanation helps in the understanding of the linear shrinkage behavior. The loss on fire reduction with the SSW incorporation consequently causes the reduction of the firing linear shrinkage. This behavior assists in the ceramic production favoring the better control of the dimensions of the products, besides, of course, to avoid defects during the drying and

**Figure 10.** Dried and sintered bulk density of formulations containing steel sludge waste [15].

**Element Solubilized (mg/L) Limits (mg/L) Leached (mg/L) Limits (mg/L)** Al 1.8 0.2 19 Not required

Recycling of Steelmaking Plant Wastes in Clay Bricks http://dx.doi.org/10.5772/intechopen.74431 35

Cu 0.004 2.0 0.13 Not required Fe 0.02 0.3 0.22 Not required Mn 0.02 0.1 0.9 Not required Na 10 200 — Not required

Zn 0.02 5.0 1.3 Not required

**Table 3.** Potentially toxic metals in the leaching and solubilization extracts of the ceramic with 5% of incorporated steel

Ba 0.06 0.7 0.7 7.0 Cd <0.003 0.005 0.04 0.5 Cr (total) <0.02 0.05 <0.05 5.0

Pb <0.06 0.1 0.14 1.0

The flexural rupture strength is also represented in **Figure 11**. Although the residue incorporation does not greatly affect the open porosity of the sintered ceramics, the mechanical

sintering stages.

sludge [17].


**Table 3.** Potentially toxic metals in the leaching and solubilization extracts of the ceramic with 5% of incorporated steel sludge [17].

**Figure 10.** Dried and sintered bulk density of formulations containing steel sludge waste [15].

considering the error bars, this property is little affected by the residue amount increasing. Therefore, as the open porosity of the ceramics containing residue is practically unchanged, it is correct to affirm that the partial substitution of the clay by the residue aided in the reduction of the loss on ignition. It is known that the loss on fire caused by clay is due to dehydroxylation of kaolinite to form metakaolinite; in this way, this mechanism is responsible for leaving porosity in the ceramic. When the clay is replaced by the residue, although it is reducing the content of clay minerals which are the most reactive particles and contribute most to the consolidation mechanisms during the sintering, it is also reducing the loss to fire; for this reason,

**Figure 9.** Micrograph obtained by SEM of the ceramic incorporated with 20% of steel sludge and sintered at 900° C in

**Figure 8.** Micrograph obtained by SEM of the ceramic incorporated with 5% of steel sludge and sintered at 900° C in

this property is little changed.

magnification of 500× (a) and 1000× (b) [17].

magnification of 800× [17].

34 Current Topics in the Utilization of Clay in Industrial and Medical Applications

This same explanation helps in the understanding of the linear shrinkage behavior. The loss on fire reduction with the SSW incorporation consequently causes the reduction of the firing linear shrinkage. This behavior assists in the ceramic production favoring the better control of the dimensions of the products, besides, of course, to avoid defects during the drying and sintering stages.

The flexural rupture strength is also represented in **Figure 11**. Although the residue incorporation does not greatly affect the open porosity of the sintered ceramics, the mechanical

**Figure 11.** Sintered technical properties of formulations containing steel sludge waste [15].

strength is a property that is highly dependent on the particle consolidation during the sintering step. As seen, the mineralogical composition of this residue does not favor the sintering mechanism in these temperatures evaluated. In this way, additions of up to 5% by weight of waste are acceptable so that there is no too much reduction at the product resistance.

> to the residue content increasing, principally at 1050°C. Although the ceramic clayey body was composed of highly refractory clay, the incorporation of 20% of the residue allowed the brick

Recycling of Steelmaking Plant Wastes in Clay Bricks http://dx.doi.org/10.5772/intechopen.74431 37

The firing linear shrinkage, represented at **Figure 14**, shows that the PMW addition doesn't contribute to the increasing of this property; it is therefore a residue capable of assisting in the

In **Figure 15**, the mechanical resistance of the ceramics with PMW addition is represented. This residue with content lower than 20% was able to improve this property at all sintering

The mineralogical constitution of the PMW, which contains high amount of iron compounds, suggests an inert behavior during the sintering stage of red clay-based ceramics. Therefore, the explanation of how the residue may have acted to improve the properties may be based on dry bulk density. Probably the combination of these two raw materials helps in the better packaging at conformation stage favoring greater points of contact between the grains. Thus, there will be less void spaces which are responsible for the water absorption reduction and

**Figure 16** represents the SEM micrograph of ceramic with 0% of residue content and fired at 1050°C. The points located at this figure are derived from EDS analysis. The micrograph shows the intrinsic porosity probably related with void spaces left after the conformation step and consolidated as pores after sintering. The presence of pores can be associated with the dehydroxylation of some hydroxides and clay minerals and also with the different expansion

production at sintering temperature of 750°C and tiles at 900°C.

dimensional control of the products.

**Figure 12.** Particle size distribution of the PMW [19].

temperatures investigated.

mechanical resistance increasing.

#### *2.2.3. Dust*

Dusts are obtained in the dry cleaning systems of process gases from the sintering stage of an integrated steelmaking plant, here denoted as PMW (particulate material waste). **Table 4** shows the chemical composition of the PMW, which is predominantly formed by iron compounds such as hematite and magnetite. CaO and SiO2 also present relatively high amounts. The loss on ignition is predominantly associated with the combustion of coke fines and the decomposition of both calcite and dolomite. The amount of 2.28% of SO<sup>3</sup> suggests the presence of sulfates, possible of Ca, such as gypsum.

In **Figure 12**, the particle size distributions of the PMW with no crush processing are represented. It should be emphasized that this particle size distribution prevents its reuse in the process to which it originated. However, for reddish ceramic industry, this characteristic is ideal, since this residue can be used directly without undergoing any other crush processing.

**Figures 13**–**15** show the graphs corresponding to the results of the technological properties after firing. A remarkable behavior can be noted with the water absorption (**Figure 13**) reduction due


**Table 4.** Chemical composition of the particulate material waste (wt.%) [18].

**Figure 12.** Particle size distribution of the PMW [19].

**Fetotal SiO2 MnO SO3 Al2**

\*

Loss on ignition.

*2.2.3. Dust*

**O3 K2**

decomposition of both calcite and dolomite. The amount of 2.28% of SO<sup>3</sup>

**Table 4.** Chemical composition of the particulate material waste (wt.%) [18].

pounds such as hematite and magnetite. CaO and SiO2

ence of sulfates, possible of Ca, such as gypsum.

70.70 6.82 0.82 2.28 1.20 1.81 10.33 9.70 0.72 3.30 10.70

strength is a property that is highly dependent on the particle consolidation during the sintering step. As seen, the mineralogical composition of this residue does not favor the sintering mechanism in these temperatures evaluated. In this way, additions of up to 5% by weight of

Dusts are obtained in the dry cleaning systems of process gases from the sintering stage of an integrated steelmaking plant, here denoted as PMW (particulate material waste). **Table 4** shows the chemical composition of the PMW, which is predominantly formed by iron com-

The loss on ignition is predominantly associated with the combustion of coke fines and the

In **Figure 12**, the particle size distributions of the PMW with no crush processing are represented. It should be emphasized that this particle size distribution prevents its reuse in the process to which it originated. However, for reddish ceramic industry, this characteristic is ideal, since this residue can be used directly without undergoing any other crush processing. **Figures 13**–**15** show the graphs corresponding to the results of the technological properties after firing. A remarkable behavior can be noted with the water absorption (**Figure 13**) reduction due

waste are acceptable so that there is no too much reduction at the product resistance.

**Figure 11.** Sintered technical properties of formulations containing steel sludge waste [15].

36 Current Topics in the Utilization of Clay in Industrial and Medical Applications

**O MgO CaO ZnO C LoI\***

also present relatively high amounts.

suggests the pres-

to the residue content increasing, principally at 1050°C. Although the ceramic clayey body was composed of highly refractory clay, the incorporation of 20% of the residue allowed the brick production at sintering temperature of 750°C and tiles at 900°C.

The firing linear shrinkage, represented at **Figure 14**, shows that the PMW addition doesn't contribute to the increasing of this property; it is therefore a residue capable of assisting in the dimensional control of the products.

In **Figure 15**, the mechanical resistance of the ceramics with PMW addition is represented. This residue with content lower than 20% was able to improve this property at all sintering temperatures investigated.

The mineralogical constitution of the PMW, which contains high amount of iron compounds, suggests an inert behavior during the sintering stage of red clay-based ceramics. Therefore, the explanation of how the residue may have acted to improve the properties may be based on dry bulk density. Probably the combination of these two raw materials helps in the better packaging at conformation stage favoring greater points of contact between the grains. Thus, there will be less void spaces which are responsible for the water absorption reduction and mechanical resistance increasing.

**Figure 16** represents the SEM micrograph of ceramic with 0% of residue content and fired at 1050°C. The points located at this figure are derived from EDS analysis. The micrograph shows the intrinsic porosity probably related with void spaces left after the conformation step and consolidated as pores after sintering. The presence of pores can be associated with the dehydroxylation of some hydroxides and clay minerals and also with the different expansion

**Figure 13.** Water absorption of the clayey body as a function the amount of the PMW incorporated [19].

coefficients among the ceramic phases during the sintering stage. Due to the refractory nature of this clay, the sintering is impaired as well as the reduction of pores, event at temperatures

Recycling of Steelmaking Plant Wastes in Clay Bricks http://dx.doi.org/10.5772/intechopen.74431 39

**Figure 15.** Flexural rupture strength of the clayey body as a function the amount of the PMW incorporated [19].

The EDS spectrum of point 1 indicates the existence of Zr and Si that can correspond to zircon silicate. Punctual regions 2 and 3 are basically composed of Si, Al, and Fe, i.e., the basic constituents

**Figure 16.** SEM micrograph of ceramic with 0 wt.% of steel dust incorporated and sintered at 1050°C, including EDS

around 1050°C.

spectra of selected points [18].

**Figure 14.** Linear shrinkage of the clayey body as a function the amount of the PMW incorporated [19].

**Figure 15.** Flexural rupture strength of the clayey body as a function the amount of the PMW incorporated [19].

**Figure 13.** Water absorption of the clayey body as a function the amount of the PMW incorporated [19].

38 Current Topics in the Utilization of Clay in Industrial and Medical Applications

**Figure 14.** Linear shrinkage of the clayey body as a function the amount of the PMW incorporated [19].

coefficients among the ceramic phases during the sintering stage. Due to the refractory nature of this clay, the sintering is impaired as well as the reduction of pores, event at temperatures around 1050°C.

The EDS spectrum of point 1 indicates the existence of Zr and Si that can correspond to zircon silicate. Punctual regions 2 and 3 are basically composed of Si, Al, and Fe, i.e., the basic constituents

**Figure 16.** SEM micrograph of ceramic with 0 wt.% of steel dust incorporated and sintered at 1050°C, including EDS spectra of selected points [18].

It can be concluded by the influence investigation of the steel sludge as raw material for ceramic production in that its incorporation is technically feasible. The porous agglomerate constituents of the steel sludge do not adhere to the clayey matrix, creating regions of failure that contribute to the reduction of the mechanical strength of the final products with incorporations of residue above 5% by weight. The environmental evaluation shows excess of Al in the solubilization extract, coming from the clay. The other evaluated elements are within the limits required for both the solubilization tests and the leaching test. The fine steel sludge is a waste predominantly composed of Fe metallic, Fe oxides (magnetite and wustite), and calcium carbonate (calcite). This waste shows a fine particle size, average of 35.6 μm that is appropriate for red clay-based ceramic production. This waste contributes to increase the dried bulk density of the ceramic. Incorporations of 5 wt.% of the waste are beneficial to the ceramic since it decreased the fired linear shrinkage and does not increase the water absorption. And also, the mechanical strength

Recycling of Steelmaking Plant Wastes in Clay Bricks http://dx.doi.org/10.5772/intechopen.74431 41

does not decrease which is also a convenient result for this level of incorporation.

ics with real benefits both in the processing and in the quality of the products.

\*, Lucas Fonseca Amaral<sup>1</sup>

**Acknowledgements**

acknowledged.

**Author details**

Brazil

Carlos Maurício F. Vieira1

\*Address all correspondence to: vieira@uenf.br

UENF, Campos dos Goytacazes, RJ, Brazil

The incorporation of a particulate, PMW, waste generated in the sintering stage of an integrated steelmaking plant, caused significant changes in a kaolinitic clay-based ceramic sintered at 1050°C. Relatively large dark phases associated with Fe and Ca compounds in the waste were formed in the clayey ceramic matrix. These phases showed evidences of microcracks- and pores-induced defects. The PMW incorporation results not only in an increased amount of porosity but also pores with relatively larger sizes. It is suggested that the inert nature of the waste, as well as its different coefficient of thermal expansion with respect to the aluminum silicate matrix, is responsible for the additional defects produced in the clayey ceramic. It was found that the particulate material waste from the sintering stage of an integrated steelmaking plant has an elevated amount of Fe and Ca compounds. The incorporation of this waste, in amounts of up to 20 wt.%, into a clayey body did not change its workability and enhanced the evaluated physical and mechanical properties such as water absorption and flexural rupture strength. The results indicated that this type of waste has a potential to be used into red ceram-

The financial support provided by the Brazilian agencies, FAPERJ and CNPq, is gratefully

1 Advanced Materials Laboratory, LAMAV, State University of the Northern Rio de Janeiro,

2 Department of Materials Science, Military Institute of Engineering, IME, Rio de Janeiro, RJ,

and Sergio N. Monteiro<sup>2</sup>

**Figure 17.** SEM micrographs of ceramic with 20 wt.% of steel dust incorporated and sintered at 1050°C, including EDS spectra of selected points [18].

of a kaolinitic clay. In this case, the Si and al predominantly constitute the aluminosilicate amorphous clayey matrix.

**Figure 17** shows two SEM micrographs of ceramic specimen with 20 wt.% of dust steel waste incorporated, sintered at 1050°C. In this figure selected punctual regions, marked in the micrographs, were analyzed by EDS. In both micrographs of **Figure 17**, defects associated with microcracks and pores can be observed.

As already mentioned for the microstructure of ceramics with no dust waste addition (**Figure 16**), these defects are associated with the conformation step and further consolidation on sintering. It is important to notice in relation to **Figure 17** that the main microstructural distinction between the ceramics with residue addition and those with no waste (**Figure 16**) is the relatively larger particles apparently belonging to the waste. In fact, the EDS spectrum of the large particle in **Figure 17** (a) indicates the presence of Ca and Fe that are, as listed in **Table 4**, characteristics of the PMW. Moreover, the microcracks that surround the particles indicate that this residue can lead to occasional defects in ceramics.

It is correct mentioning that, in spite of the defects observed, this waste acts as an inert material and assists on the plasticity control of the clayey body. Despite the inert character of the residue particles, the observed microcracks (**Figure 16(a)**) may be associated due their different expansion coefficient at sintering stage, more pronounced at 1050°C. The particle analyzed in **Figure 16(b)** is relatively small and by its EDS spectrum, with Si and O, corresponds to a quartz particle, which already exists in the natural clay.
