**1. Introduction**

The history of integrated factory's steel product usually begins from a preparation of a sinter being one of the main component of a blast-furnace charge. In blastfurnace practice a sinter is a product after high temperature treatment of a mixture of iron ores and their concentrates, fluxing agents (dolomite, lime) and coke breeze. Sintering process takes place in a range of 1200–1300°C and causes partial melting of individual grains of all sinter's components, forming a compact product. The temperature has to be lower than a melting point of the mixture. There are some phase transformations and/or degradation of minerals which accompany the sintering processes. As a result, a mineralogy of a sinter is different than a mineralogy of starting components.

Generally, the mineralogy of sinters can be thought as a mineralogy of two types of compounds: oxides and silicates, including also silicate glass. The presence and the amount of individual minerals depend on the properties of and the conditions of technology (practice). One of the most important factor, characterizing a sinter, is its basicity; the value of this parameter is defined as a ratio of a content of calcium (given as calcium oxide) to a content of silicon (given as silicon dioxide).

The basicity of a sinter is the main reason of diversity in observed mineral composition and – consequently – in properties of the sinter.

The identification of mineral components can be done using various experimental techniques from which the X-ray diffraction seems to be the most important. Every crystalline chemical compound (mineral) produces its own, typical X-ray diffraction pattern which can be used in identification of it in a multiphase mixture. The individual patterns are kept in Powder Diffraction File, updated every year by the International Centre for Diffraction Data and having now (2020) more than 400,000 data of inorganic compounds. In many cases, the data for one particular compound contains also information about crystallography of this compound. It means that a calculation of a theoretical pattern of this compound is possible. In X-ray diffraction method, one can assume that the observed pattern of a multiphase powder mixture is a sum of weighed patterns of individual compounds (minerals). This assumption gives the possibility to apply the Rietveld method to study the multiphase mixtures and to calculate the fractions of individual components of the mixture.

The Rietveld method was presented for the first time in 1967 by H. Rietveld to refine crystallographic structure of a crystalline compound, using neutron diffraction [1, 2]. R. A. Young and D. B. Wiles applied the method to X-ray diffraction in 1981 [3, 4] and the next application to quantitative phase analysis was introduced by Hill and Howard in 1987 [5] and Bish and Howard in 1988 [6]. The crucial advantage of the Rietveld method in studying and quantifying mixtures is the ability to analyze the overlapped reflections. Overlapping is the most important problem in mixtures, especially in the case of low symmetry of constituents. The number of reflections can reach some hundreds in a typical 2Theta range of measurements. There is also another problem – a contribution of intensities of many small reflections to an observed intensity of a background of an experimental X-ray diffraction pattern and consequently some difficulties in refining the background. This is also the case of the presence of amorphous component. This matter was solved in the Siroquant software [7] in which the shape and intensity of the background is not refined but manually removed from a pattern. Owing to the above, the Rietveld method gives the unique opportunity for a precise quantitative description of blast furnace sinters.

The quality of sinter's pieces can be described using different indices which have to be determined by some technical tests and experiments, according to international standards [8].

The tests are carried out in conditions which simulate blast-furnace's conditions in upper part of its shaft. A sample of a sinter of 500 g is placed into a furnace heated up to 500÷550°C and is exposed to a reducing gas for 60 minutes. Then the sinter is cooled in an atmosphere of inert gas and is subjected to tumbling. The disintegration sinter's pieces gives grains of various sizes which are screened to three groups. The following indices, according to International Standard ISO 4696- 1:2007, are determined:

Static resistance to degradation (the ratio of reduced sinter with size larger than 6.3 mm after tumbling test to reduced sinter)

$$RDI - \mathbf{1}\_{\ast \colon \mathbf{3}} = \frac{m\_1}{m\_0} \times \mathbf{100\%} \tag{1}$$

**81**

**Figure 1.**

**1.1 Materials**

*Application of X-Ray Diffraction to Study Mineralogical Dependence of Reduction…*

3.15

0.5

*m* <sup>−</sup>

Static grindability (the difference between reduced sinter and the sum of reduced sinter with size larger than 6.3 mm, reduced sinter with size larger than 3.15 mm and reduced sinter with size larger than 0.5 mm divided by reduced sinter)

*m* <sup>−</sup>

of oversize particles remained on a screen of 3.15 mm after tumbling.

quantitative mineral composition of blast furnace sinters on their quality.

were calculated according to the procedure given above.

*Samples of hematite lump ore (a), magnetite concentrate (b) and sinter (c).*

*RDI*

*RDI*

0 12 ( )

− + −= × (2)

− ++ − = <sup>×</sup> (3)

0 1 100% *m mm*

0 123 ( )

0 1 100% *m mmm*

where: m0 [g] – mass of a sample after reduction before tumbling m1 [g] – mass of oversize particles remained on a screen of 6.3 mm after tumbling m2 [g] – mass

m3 [g] – mass of oversize particles remained on a screen 0.5 mm after tumbling. From technological point of view, the most important index is a static susceptibility to degradation and a question of dependence of its value on a mineralogical composition of a sinter is still to be answered. Previous examinations showed that there was a connection between quantities of mineral components of sinters and their reducibilities [9] and this work is a continuation of studying a dependence of

All sinters were prepared from raw materials which were used in Polish steel plants. There were two kinds of iron ores and three kinds of concentrates of other iron ores (**Figure 1**). Six different mixtures were prepared, each one consisted of different combinations of ores and concentrates but with a planned basicity (**Table 1**). Basicity was calculated as a ratio of calcium content recalculated to CaO to silicon content given as SiO2. Sintering process was carried out in laboratory conditions with application of lime and dolomite in a conventional sinter pot of a diameter of 490 mm [10]. Ten laboratory tests were done for each kind of mixture (**Figure 2**); then three samples characterized by optimal moisture with the highest productivity were selected for further investigations (**Table 2**). The RDI values

*DOI: http://dx.doi.org/10.5772/intechopen.95086*

Static susceptibility to degradation (the difference between reduced sinter and the sum of reduced sinter with size larger than 6.3 mm and reduced sinter with size larger than 3.15 mm divided by reduced sinter)

*Application of X-Ray Diffraction to Study Mineralogical Dependence of Reduction… DOI: http://dx.doi.org/10.5772/intechopen.95086*

$$RDI - \mathbf{1}\_{-3.15} = \frac{m\_0 - \left(m\_1 + m\_2\right)}{m\_0} \times \mathbf{100\%} \tag{2}$$

Static grindability (the difference between reduced sinter and the sum of reduced sinter with size larger than 6.3 mm, reduced sinter with size larger than 3.15 mm and reduced sinter with size larger than 0.5 mm divided by reduced sinter)

$$RDI - \mathbf{1}\_{\text{-0.5}} = \frac{m\_0 - \left(m\_1 + m\_2 + m\_3\right)}{m\_0} \times \mathbf{100\%} \tag{3}$$

where: m0 [g] – mass of a sample after reduction before tumbling m1 [g] – mass of oversize particles remained on a screen of 6.3 mm after tumbling m2 [g] – mass of oversize particles remained on a screen of 3.15 mm after tumbling.

m3 [g] – mass of oversize particles remained on a screen 0.5 mm after tumbling. From technological point of view, the most important index is a static susceptibility to degradation and a question of dependence of its value on a mineralogical composition of a sinter is still to be answered. Previous examinations showed that there was a connection between quantities of mineral components of sinters and their reducibilities [9] and this work is a continuation of studying a dependence of quantitative mineral composition of blast furnace sinters on their quality.

#### **1.1 Materials**

*Iron Ores*

The basicity of a sinter is the main reason of diversity in observed mineral composi-

The identification of mineral components can be done using various experimental techniques from which the X-ray diffraction seems to be the most important. Every crystalline chemical compound (mineral) produces its own, typical X-ray diffraction pattern which can be used in identification of it in a multiphase mixture. The individual patterns are kept in Powder Diffraction File, updated every year by the International Centre for Diffraction Data and having now (2020) more than 400,000 data of inorganic compounds. In many cases, the data for one particular compound contains also information about crystallography of this compound. It means that a calculation of a theoretical pattern of this compound is possible. In X-ray diffraction method, one can assume that the observed pattern of a multiphase powder mixture is a sum of weighed patterns of individual compounds (minerals). This assumption gives the possibility to apply the Rietveld method to study the multiphase mixtures

The Rietveld method was presented for the first time in 1967 by H. Rietveld to refine crystallographic structure of a crystalline compound, using neutron diffraction [1, 2]. R. A. Young and D. B. Wiles applied the method to X-ray diffraction in 1981 [3, 4] and the next application to quantitative phase analysis was introduced by Hill and Howard in 1987 [5] and Bish and Howard in 1988 [6]. The crucial advantage of the Rietveld method in studying and quantifying mixtures is the ability to analyze the overlapped reflections. Overlapping is the most important problem in mixtures, especially in the case of low symmetry of constituents. The number of reflections can reach some hundreds in a typical 2Theta range of measurements. There is also another problem – a contribution of intensities of many small reflections to an observed intensity of a background of an experimental X-ray diffraction pattern and consequently some difficulties in refining the background. This is also the case of the presence of amorphous component. This matter was solved in the Siroquant software [7] in which the shape and intensity of the background is not refined but manually removed from a pattern. Owing to the above, the Rietveld method gives the unique opportunity for a precise quantitative description of blast

The quality of sinter's pieces can be described using different indices which have to be determined by some technical tests and experiments, according to interna-

Static resistance to degradation (the ratio of reduced sinter with size larger than

1

*<sup>m</sup>* − =× <sup>+</sup> (1)

0

6.3

1 100% *<sup>m</sup> RDI*

Static susceptibility to degradation (the difference between reduced sinter and the sum of reduced sinter with size larger than 6.3 mm and reduced sinter with size

The tests are carried out in conditions which simulate blast-furnace's conditions in upper part of its shaft. A sample of a sinter of 500 g is placed into a furnace heated up to 500÷550°C and is exposed to a reducing gas for 60 minutes. Then the sinter is cooled in an atmosphere of inert gas and is subjected to tumbling. The disintegration sinter's pieces gives grains of various sizes which are screened to three groups. The following indices, according to International Standard ISO 4696-

and to calculate the fractions of individual components of the mixture.

tion and – consequently – in properties of the sinter.

**80**

furnace sinters.

tional standards [8].

1:2007, are determined:

6.3 mm after tumbling test to reduced sinter)

larger than 3.15 mm divided by reduced sinter)

All sinters were prepared from raw materials which were used in Polish steel plants. There were two kinds of iron ores and three kinds of concentrates of other iron ores (**Figure 1**). Six different mixtures were prepared, each one consisted of different combinations of ores and concentrates but with a planned basicity (**Table 1**). Basicity was calculated as a ratio of calcium content recalculated to CaO to silicon content given as SiO2. Sintering process was carried out in laboratory conditions with application of lime and dolomite in a conventional sinter pot of a diameter of 490 mm [10]. Ten laboratory tests were done for each kind of mixture (**Figure 2**); then three samples characterized by optimal moisture with the highest productivity were selected for further investigations (**Table 2**). The RDI values were calculated according to the procedure given above.

**Figure 1.** *Samples of hematite lump ore (a), magnetite concentrate (b) and sinter (c).*


#### **Table 1.**

*The planned basicity values of each kind of mixtures.*

#### **Figure 2.**

*The experimental site for sintering iron ores and waste products in Sie*ć *Badawcza* Ł*ukasiewicz - Instytut Metalurgii* Ż*elaza.*


**Table 2.**

*The RDI values of the chosen sinters.*
