ON THE RELATIONSHIP BETWEEN COMPONENTS IN IRON ORES OF THE TASHTAGOL DEPOSIT

P. I. Raiskii

(Presented by the scientific seminar of the Department of Mine Surveying and Geodesy)

The study of the chemical-technological composition of iron ores is of great practical importance for metallurgy. Meanwhile, in the geological literature on deposits of Gornaya Shoria this question has been treated with insufficient completeness for practical purposes.

As a rule, the literature indicates only the limits of variation in the content of the various components in the ore. For example, for the ores of the Tashtagol deposit it is stated that their content of $\mathrm{SiO_2}$ varies from 6 to 18%. The same is said with respect to $\mathrm{CaO}$, $\mathrm{Al_2O_3}$, and other components.

In the literature not a word is said about how the content of $\mathrm{SiO_2}$, $\mathrm{CaO}$, and other components changes in ores with different iron contents; therefore metallurgists reproach geologists for giving an incomplete characterization of the material composition of iron ores.

To study the material composition of iron ores during the period of exploration and exploitation of a deposit, dozens, and sometimes hundreds, of analyses are carried out for the various components that enter into their composition. However, these rich data, without their corresponding analysis, likewise do not fully reveal the picture of the quantitative changes of the various components in ores with different iron contents.

If, however, the regular interrelationships between the various components in iron ores are studied, these interrelationships will reveal the picture of how the content of the various components changes depending on the change in their iron content.

Knowledge of the interrelationships between the various components in iron ores will make it possible to reduce the number of analyses for their determination, and will facilitate the process of averaging ores during their extraction, which is very important for obtaining ore raw material with a constant chemical-mineralogical composition.

The use of averaged ore raw material in metallurgy, in turn, will improve the operation of the blast furnace and increase the coefficient of metal extraction from the ore.

Relationship of $\mathrm{SiO_2}$, $\mathrm{CaO}$, $\mathrm{Al_2O_3}$, and $\mathrm{MgO}$ with Fe and $\mathrm{Fe_2O_3}$

In work [1] we indicated that in the iron ores of the deposits of Gornaya Shoria the content of most of the components entering

included in their composition is inversely dependent on the content of ore iron Fe in them; that is, with an increase in the iron content in the ore, the content of the components decreases.

Further studies of the interrelationships between the components showed that the amount of SiO₂, CaO, Al₂O₃, and MgO in the ore also depends on its content of FeO and Fe₂O₃.

In different grades of iron ore, at one and the same content of ore iron, the amount of FeO and Fe₂O₃ is different. If the FeO content in the ore decreases, then the Fe₂O₃ content increases and, conversely, with an increase in the FeO content, the Fe₂O₃ content in the ore decreases.

In both the first and the second cases, the amount of SiO₂, CaO, Al₂O₃, and MgO also decreases or increases. Thus, the content of the above-mentioned oxides in the ore is a function of its content of FeO and Fe₂O₃.

To study the question of how changes in the amount of FeO and Fe₂O₃ in the ore affect the content of other components in it, we constructed graphs of the dependence of the content of the oxides SiO₂, CaO, Al₂O₃, and MgO in the ore on its content of FeO and Fe₂O₃. Two such graphs are shown in Figs. 1 and 2.

Fig. 1. Graph of the dependence of the CaO content in the ore on its FeO content.

Studies showed that the content of the oxides SiO₂, CaO, Al₂O₃, and MgO in iron ores is in an inverse, almost rectilinear dependence on their content of FeO and Fe₂O₃. At the same time, it was established that all the above-mentioned oxides, both with FeO and with Fe₂O₃, have two clearly expressed regions of correlation dependence, which are shifted relative to one another (Figs. 1, 2).

The upper correlation relationship of SiO₂, CaO, Al₂O₃, and MgO with FeO and Fe₂O₃ is characteristic of iron ores in which the content of FeO and Fe₂O₃ is equal to or close to the content of FeO and Fe₂O₃ for pure magnetite ores.

For pure magnetites, the content of FeO and Fe₂O₃ can be calculated by the formulas

\[ \mathrm{FeO}_M = 0.43\,\mathrm{Fe}_{\text{ore}}, \tag{1} \]

\[ \mathrm{Fe}_2\mathrm{O}_{3M} \cong \mathrm{Fe}_{\text{ore}}. \tag{2} \]

Fig. 2. Graph of the dependence of the Al₂O₃ content in the ore on the Fe₂O₃ content in it.

Relation (1) is known from textbooks of analytical chemistry. The parameters of equality (2) were determined by us by the method of correlation theory from 430 analyses. The calculations are not given here.

The lower region of the correlation relationship of the oxides SiO₂, CaO, Al₂O₃, and MgO with FeO and Fe₂O₃ corresponds to those ores in which the contents of FeO and Fe₂O₃ differ sharply from the FeO and Fe₂O₃ contents calculated by formulas (1) and (2).

For practical purposes it is important to know not only the form, but also the degree of reliability of the interrelationship between the components. The degree of reliability of a rectilinear correlation relationship is assessed by means of the correlation coefficient. If the correlation coefficient is close to unity or equal to unity, then there is a rectilinear relationship between the components.

The investigations showed that the degree of reliability of the relationship of the oxides SiO₂, CaO, Al₂O₃, and MgO with Fe₂O₃ is sufficiently high, since the correlation coefficients are, in magnitude, close to unity (Table 1). The relationship of CaO with Fe₂O₃ is especially good (the correlation coefficient is equal to 0.97).

With FeO, the oxides of silicon, aluminum, and others have a weaker relationship than with Fe₂O₃. In particular, the relationship of metal oxides with FeO will be poor if the relationship between them is considered as a single statistical population, i.e., if it is not divided into two regions. In this case, in individual samples the maximum deviation of the CaO content in the ore from the CaO value calculated from the smoothed curve is more than 5%.

Thus, the investigations have established (Figs. 1, 2) that the amounts of FeO and Fe₂O₃ in iron ores substantially influence the formation of the number of regions of interrelationship among the oxides SiO₂, CaO, Al₂O₃, and MgO. For each region, the components SiO₂ and others are interrelated in different quantitative ratios, which is confirmed by the research data given below.

Table 1

Assessment of the reliability of the relationship of SiO₂, CaO, Al₂O₃, and MgO with Fe, Fe₂O₃, and (FeO + Fe₂O₃)

Relationship among the oxides SiO₂, CaO, Al₂O₃, and MgO. A characterization of the material composition of iron ores will be more complete if we study the question of the quantitative relationships in which the components SiO₂, CaO, Al₂O₃, and MgO that make up their composition are connected.

To resolve this question, we constructed various graphs, namely:

a) graphs of the dependence of the content in the ore of CaO, Al₂O₃, and MgO on the content in it of SiO₂;

b) graphs of the dependence of the content in the ore of Al₂O₃ and MgO on the content in it of CaO;

c) a graph of the dependence of the content in the ore of MgO on the content in it of Al₂O₃.

One of these graphs, as an example, is given in Fig. 3 (see p. 114).

The construction of the graphs showed that between the oxides SiO₂, CaO, and others there is an almost rectilinear dependence. At the same time it should be noted that, in the iron ores, we established two regions of correlation relationship: SiO₂ with CaO, Al₂O₃, and MgO; CaO with Al₂O₃ and MgO; and Al₂O₃ with MgO, which are displaced parallel to one another (Fig. 3).

The upper correlation relationship between the oxides Si, Ca, Al, and Mg pertains to those iron ores in which the FeO and Fe₂O₃ content is equal or close to the FeO and Fe₂O₃ content for pure magnetites (Fig. 3).

The lower region of the correlation relationship among the above-listed components is characteristic of ores in which the FeO and Fe₂O₃ content is either greater or less than in pure magnetite ores. Each of these correlation relationships pertains to different ore types.

Since in each ore type the components SiO₂, CaO, Al₂O₃, and MgO are interrelated in different quantitative ratios, the relationship

between them must be established separately for each ore variety.

The degree of relationship between the oxides SiO₂, CaO, Al₂O₃, and MgO is sufficiently high, since the correlation coefficients are close in magnitude to unity (Table 2). The relationship of SiO₂ with MgO and CaO, and of Al₂O₃ with MgO, is especially good.

Fig. 3. Graph of the dependence of the CaO content in the ore on the SiO₂ content in it.

Table 2

Assessment of the reliability of the relationship between the components
SiO₂, CaO, Al₂O₃, MgO

Studies have established that the most advantageous function for expressing these relationships in analytical form is an exponential function of the form

\[ y = Ae^{Bx} + C, \tag{3} \]

where \(e\) is the base of natural logarithms.

For the various relationships, we determined, by the method of means, the parameters \(C\), \(A\), and \(B\) of formula (3). The results of the determination are presented in Table 3.

Verification of the parameters of the formulas in Table 3 was carried out by comparing the contents of Al₂O₃ and MgO in the ore, calculated by formulas (3Б)—(3Е).

Table 3

Empirical formulas expressing the relationship between SiO₂, CaO, Al₂O₃, and MgO in analytical form

Note: 1) 26, 3.2, 7.45 are coefficients numerically equal to the average content in the earth’s crust of Si, Ca, and Al, % (according to the diagram in work (2)).
2) The values of SiO₂, CaO, and Al₂O₃ in formulas (3А)—(3Е) of Table 3 are in relative units.

The difference in the contents of Al₂O₃ and MgO in the ore, calculated by different formulas, proved to be insignificant (Table 4).

Relationship of SiO₂, CaO, Al₂O₃, and MgO with (FeO + Fe₂O₃)

Comparing the results of analyses of iron ore for various components, it was noted that in those samples in which the FeO content in the ore is less than the FeO content calculated by formula (1), the Fe₂O₃ content in these samples is greater than the Fe content of the ores. Conversely, in those samples in which the FeO content in the ore is greater than the FeO calculated by formula (1), the Fe₂O₃ content in such samples is less than the Fe content of the ores.

In both the first and the second cases, the contents of SiO₂, CaO, Al₂O₃, and MgO in the ore vary greatly; therefore, we investigated the correlation relationship of these components with (FeO + Fe₂O₃).

[Figure: graph with vertical axis “SiO₂ content in ore, %” and horizontal axis “(FeO + Fe₂O₃) content in ore, %”; plotted points and a decreasing curve labeled 1.]

Fig. 4. Graph of the dependence of the SiO₂ content in the ore on the content in it of (FeO + Fe₂O₃).

Graphs were constructed for the dependence of the oxides of Si, Ca, Al, and Mg on (FeO + Fe₂O₃), and the reliability of the relationship between them was evaluated (Table 1). One such graph is shown in Fig. 4.

Table 4

Comparative table of the contents of CaO, Al₂O₃, and MgO in the ore, calculated by formulas (3A)—(3E)

Studies have shown that the relationship of \(\mathrm{SiO_2}\), \(\mathrm{CaO}\), \(\mathrm{Al_2O_3}\), and \(\mathrm{MgO}\) with \((\mathrm{FeO}+\mathrm{Fe_2O_3})\) is inverse, almost rectilinear, and sufficiently reliable.

The degree of reliability of the relationship of the oxides of Si, Ca, Al, and Mg with \((\mathrm{FeO}+\mathrm{Fe_2O_3})\) is higher than with ore Fe. This can be judged from the values of the correlation coefficients in Table 1. The better relationship of \(\mathrm{SiO_2}\), \(\mathrm{CaO}\), \(\mathrm{Al_2O_3}\), and \(\mathrm{MgO}\) with \((\mathrm{FeO}+\mathrm{Fe_2O_3})\) than with ore Fe is well confirmed by the graph in Fig. 4 and by others, which are not presented here. The contents of the oxides of Si, Ca, Al, and Mg in individual samples according to analyses, relative to the calculated contents by formulas (4)—(7), do not exceed the following limits: for \(\mathrm{SiO_2}\)—2%, \(\mathrm{CaO}\)—1.5%, \(\mathrm{Al_2O_3}\)—1%, and \(\mathrm{MgO}\)—0.2%. For the relationships of \(\mathrm{SiO_2}\), \(\mathrm{CaO}\), \(\mathrm{Al_2O_3}\), and \(\mathrm{MgO}\) with ore Fe, these limits of deviation are twice as large.

In analytical form, for magnetite ores the relationship of \(\mathrm{SiO_2}\), \(\mathrm{CaO}\), \(\mathrm{Al_2O_3}\), and \(\mathrm{MgO}\) with \((\mathrm{FeO}+\mathrm{Fe_2O_3})\) can be expressed by the following empirical formulas:

\[ \mathrm{SiO_2},\% = 85 e^{-1.166(\mathrm{FeO}+\mathrm{Fe_2O_3})} - 26; \tag{4} \]

\[ \mathrm{CaO},\% = 29.2 - 15.2 e^{0.7(\mathrm{FeO}+\mathrm{Fe_2O_3})}; \tag{5} \]

\[ \mathrm{Al_2O_3},\% = 27 e^{-1.35(\mathrm{FeO}+\mathrm{Fe_2O_3})} - 7.45; \tag{6} \]

\[ \mathrm{MgO},\% = 6.52 e^{-0.96(\mathrm{FeO}+\mathrm{Fe_2O_3})} - 2.35, \tag{7} \]

where \(e\) is the base of natural logarithms.

In formulas (4)—(7), \((\mathrm{FeO}+\mathrm{Fe_2O_3})\) must be taken in relative units.

Conclusions

On the basis of the obtained results of studying the relationship of the contents of the oxides \(\mathrm{SiO_2}\), \(\mathrm{CaO}\), \(\mathrm{Al_2O_3}\), and \(\mathrm{MgO}\) in iron ores with their contents of \(\mathrm{FeO}\) and \(\mathrm{Fe_2O_3}\), the following conclusions can be drawn.

1. In the iron ores of the Tashtagol deposit, the contents of \(\mathrm{SiO_2}\), \(\mathrm{CaO}\), \(\mathrm{Al_2O_3}\), and \(\mathrm{MgO}\) are in an inverse, almost rectilinear dependence on the contents in them of \(\mathrm{FeO}\) and \(\mathrm{Fe_2O_3}\). Between the contents of the oxides \(\mathrm{SiO_2}\), \(\mathrm{CaO}\), \(\mathrm{Al_2O_3}\), and \(\mathrm{MgO}\) themselves there is also a nearly rectilinear, sufficiently reliable correlation.

2. The amount of \(\mathrm{SiO_2}\), \(\mathrm{CaO}\), \(\mathrm{Al_2O_3}\), and \(\mathrm{MgO}\) in iron ores depends strongly on the degree of their oxidation, i.e., on their content of \(\mathrm{Fe_2O_3}\) and \(\mathrm{FeO}\). For each type of ore, the oxides \(\mathrm{SiO_2}\), \(\mathrm{CaO}\), \(\mathrm{Al_2O_3}\), and \(\mathrm{MgO}\) are interrelated in different quantitative ratios; therefore, the dependence among them must be established separately for each type of ore.

3. Between the content of \(\mathrm{SiO_2}\), \(\mathrm{CaO}\), \(\mathrm{Al_2O_3}\), and \(\mathrm{MgO}\) in the ore and the content in it of \((\mathrm{FeO}+\mathrm{Fe_2O_3})\), there is likewise an inverse, sufficiently reliable, almost linear dependence. The relationship of \(\mathrm{SiO_2}\) and \(\mathrm{Al_2O_3}\) with \((\mathrm{FeO}+\mathrm{Fe_2O_3})\) is especially good (the correlation coefficients are close to unity).

4. Comparing the values of the correlation coefficients in Table 1 for the relationships of the oxides \(\mathrm{SiO_2}\), \(\mathrm{CaO}\), \(\mathrm{Al_2O_3}\), and \(\mathrm{MgO}\) with Fe, \(\mathrm{Fe_2O_3}\), and \((\mathrm{Fe_2O_3}+\mathrm{FeO})\), it may be observed that the best relationship is that of \(\mathrm{SiO_2}\) and \(\mathrm{Al_2O_3}\) with \((\mathrm{FeO}+\mathrm{Fe_2O_3})\), and that of \(\mathrm{CaO}\) and \(\mathrm{MgO}\) with \(\mathrm{Fe_2O_3}\). Therefore, for practical purposes, the content in the ore of \(\mathrm{SiO_2}\) and \(\mathrm{Al_2O_3}\) is best found from the dependence of \(\mathrm{SiO_2}\) and \(\mathrm{Al_2O_3}\) on \((\mathrm{FeO}+\mathrm{Fe_2O_3})\), and that of \(\mathrm{CaO}\) and \(\mathrm{MgO}\) from the relationship of \(\mathrm{CaO}\) and \(\mathrm{MgO}\) with \(\mathrm{Fe_2O_3}\). If the indicated dependencies are used, it is possible to determine

their content in the ore with an error of $SiO_2$—2%, $Al_2O_3$—1%, $CaO$—1%, and $MgO$—0.2%.

1. The results of our studies of the correlation relationship between the components in the iron ores of the Tashtagol deposit once again confirm the validity of the words of Academician A. E. Fersman: “In the depths of the Earth there is not a chaotic accumulation of elements and their compounds, but an extraordinary order reigns, determined by regular properties and interrelations among geochemical elements” [3].

REFERENCES

1. Raiskii P. I. On the correlation relationship between components in magnetite ores of the deposits of Gornaya Shoria. Izvestiya vuzov, Gornyi zhurnal, No. 9, 1959.
2. Surveyor’s Handbook. Metallurgizdat, 1958.
3. Fersman A. E. Geochemistry, Vol. 1, 1934.