Interaction of Ilmenite with Calcium Carbonate

E. P. Solomatina, P. G. Usov

(Presented by the scientific seminar of the Department of Technology of Silicates, Inorganic Substances, and Electrochemical Production)

The study of the interaction of calcium oxide with titanium dioxide has been carried out for various purposes.

Loshkarev [1] studied the effect of titanium dioxide on the sintering of lime. He concluded that the strongest sintering action is observed with the addition of 3–3.5% titanium dioxide and, at the same time, the sintering temperature of lime is significantly reduced.

In carrying out studies on the production of titanium cements, Ershov [2] studied the compositions and properties of calcium titanates. The phase diagram of the system CaO—TiO₂ has at present been insufficiently studied. The compounds in this system that are indisputably established and well studied are CaTiO₃—perovskite—and Ca₃Ti₂O₇ [3]. These compounds and the kinetics of their formation were studied by Mamykin and Loshkarev [4], who confirmed the presence of only two compounds. They concluded that the rate of the reaction forming calcium monotitanate is approximately 1.5–2 times greater than the rate of formation of Ca₃Ti₂O₇; therefore, in FeTiO₃—CaO mixtures, calcium monotitanate will first form, followed by its saturation with CaO and the formation of Ca₃Ti₂O₇, capable of existing in equilibrium with CaO.

The compounds Ca₂TiO₄ and Ca₃TiO₅, shown on Berezhnoi’s diagram [5], are at present questionable.

In addition to the compounds CaTiO₃ and Ca₃Ti₂O₇, Roth [10] describes the compound Ca₄Ti₃O₁₀, which melts incongruently, forming CaTiO₃ and liquid.

We set ourselves the task of studying the process of interaction of ilmenite with calcium carbonate in order to develop a technology for the use of local raw material.

The investigation was carried out on mixtures of FeTiO₃ with CaO, taken in stoichiometric ratios of 1:1, 1:2, and 1:3. Calcium oxide was introduced in the form of chemically pure calcium carbonate. From the mixtures, tablets 14 mm in diameter and 2 mm high were pressed and fired in an electric furnace with carborundum heating elements.

The course of the reactions forming calcium titanates was monitored by determining free calcium oxide in the samples after firing, using a method in which the sample was treated with a solution of ammonium chloride [6].

The results of experiments elucidating the influence of time and temperature on the course of the reactions are given in Table 1 and shown graphically in Figs. 1 and 2.

It is seen from Table 1 that complete binding of CaO is achieved in charge 1 \((\mathrm{FeTiO_3}:\mathrm{CaCO_3}=1:1)\) after firing at 1300° and holding for 2 hours, in

![Figure 1 graph: binding of CaO by ilmenite as a function of temperature. Vertical axis: % CaO bound; horizontal axis: temperature, °C. Curves 1–3 correspond to charges FeTiO₃:CaO = 1:1, 1:2, and 1:3.]

Fig. 1. Binding of CaO by ilmenite as a function of temperature (holding time 20 min): — charge FeTiO₃:CaO = 1:1; -·- charge FeTiO₃:CaO = 1:2; —x—x— charge FeTiO₃:CaO = 1:3

![Figure 2 graph: binding of CaO by ilmenite as a function of holding time at 1300°. Vertical axis: % CaO bound; horizontal axis: holding time, min. Curves 1–3 correspond to charges FeTiO₃:CaO = 1:1, 1:2, and 1:3.]

Fig. 2. Binding of CaO by ilmenite as a function of holding time (1300°): — charge FeTiO₃:CaO = 1:1; -·- charge FeTiO₃:CaO = 1:2; —x—x— charge FeTiO₃:CaO = 1:3

Table 1

in charge 2 \((\mathrm{FeTiO_3}:\mathrm{CaCO_3}=1:2)\), the bound CaO amounts to 80%, and in charge 3 \((\mathrm{FeTiO_3}:\mathrm{CaCO_3}=1:3)\), to 60% of the theoretically introduced amount of calcium oxide.

We carried out a thermodynamic analysis of solid-phase reactions in the systems under study, with the formation of calcium titanates of different compositions.

The following reactions were considered:

\[ \begin{aligned} \mathrm{I}\quad 1)\;& \mathrm{FeTiO_3+CaCO_3=CaTiO_3+FeO+CO_2},\\ 2)\;& \mathrm{FeTiO_3+CaCO_3=\frac{1}{2}(Ca_2TiO_4)+\frac{1}{2}TiO_2+FeO+CO_2},\\ 3)\;& \mathrm{FeTiO_3+CaCO_3=\frac{1}{3}(Ca_3Ti_2O_7)+\frac{1}{3}TiO_2+FeO+CO_2},\\ 4)\;& \mathrm{FeTiO_3+CaCO_3=\frac{1}{3}(Ca_3TiO_5)+\frac{2}{3}TiO_2+FeO+CO_2},\\ 5)\;& \mathrm{FeTiO_3+CaCO_3=\frac{1}{4}(Ca_4Ti_3O_{10})+\frac{1}{4}TiO_2+FeO+CO_2}. \end{aligned} \]

\[ \begin{aligned} \mathrm{II}\quad 1)\;& \mathrm{FeTiO_3+2CaCO_3=CaTiO_3+CaO+FeO+2CO_2},\\ 2)\;& \mathrm{FeTiO_3+2CaCO_3=Ca_2TiO_4+FeO+2CO_2},\\ 3)\;& \mathrm{FeTiO_3+2CaCO_3=\frac{1}{2}Ca_3Ti_2O_7+\frac{1}{2}CaO+FeO+2CO_2},\\ 4)\;& \mathrm{FeTiO_3+2CaCO_3=\frac{1}{3}Ca_3TiO_5+\frac{1}{2}CaO+FeO+2CO_2},\\ 5)\;& \mathrm{FeTiO_3+2CaCO_3=\frac{1}{3}Ca_4Ti_3O_{10}+\frac{2}{3}CaO+FeO+2CO_2}. \end{aligned} \]

\[ \begin{aligned} \mathrm{III}\quad 1)\;& \mathrm{FeTiO_3+3CaCO_3=CaTiO_3+2CaO+FeO+3CO_2},\\ 2)\;& \mathrm{FeTiO_3+3CaCO_3=Ca_2TiO_4+CaO+FeO+3CO_2},\\ 3)\;& \mathrm{FeTiO_3+3CaCO_3=\frac{1}{2}Ca_3Ti_2O_7+\frac{3}{2}CaO+FeO+3CO_2},\\ 4)\;& \mathrm{FeTiO_3+3CaCO_3=Ca_3TiO_5+FeO+3CO_2},\\ 5)\;& \mathrm{FeTiO_3+3CaCO_3=\frac{1}{3}Ca_4Ti_3O_{10}+\frac{5}{3}CaO+FeO+3CO_2}. \end{aligned} \]

The known thermochemical data necessary for the calculation were taken from reference tables [7]; the missing quantities were calculated by the method proposed by Zharkova [8]. The values of \(\Delta Z_T\) in the temperature interval \(1200\text{--}1600^\circ\mathrm{K}\) were calculated from the following equations:

\[ \begin{aligned} \mathrm{I}\quad 1)\;& \Delta Z_T=-14240-3{,}31T\ln T+1{,}23T^2\cdot10^{-3}+0{,}36T^{-1}\cdot10^5+20{,}7T;\\ 2)\;& \Delta Z_T=-4290-2T\ln T+1{,}23T^2\cdot10^{-3}+13{,}5T;\\ 3)\;& \Delta Z_T=-6780-2{,}48T\ln T+1{,}23T^2\cdot10^{-3}+14{,}7T;\\ 4\text{--}5)\;& \Delta Z_T=5750-2{,}48T\ln T+1{,}28T^2\cdot10^{-3}+15{,}8T; \end{aligned} \]

\[ \begin{aligned} \mathrm{II}\quad 1)\;& \Delta Z_T=-14240-3{,}31T\ln T+1{,}23T^2\cdot10^{-3}+0{,}36T^{-1}\cdot10^5+20{,}7T;\\ 2)\;& \Delta Z_T=-14330-1{,}48T\ln T+1{,}23T^2\cdot10^{-3}+7T;\\ 3)\;& \Delta Z_T=-12920-2{,}48T\ln T+1{,}53T^2\cdot10^{-3}+13{,}3T;\\ 4)\;& \Delta Z_T=-4200-2{,}89T\ln T+1{,}80T^2\cdot10^{-3}+18T;\\ 5)\;& \Delta Z=5820-2{,}48T\ln T+1{,}23T^2\cdot10^{-3}+15{,}8T; \end{aligned} \]

\[ \begin{aligned} \mathrm{III}\quad 1)\;& \Delta Z_T=-14240-3{,}31T\ln T+1{,}23T^2\cdot10^{-3}+0{,}36T^{-1}\cdot10^5+20{,}7T;\\ 2)\;& \Delta Z_T=-14330-1{,}48T\ln T+1{,}23T^2\cdot10^{-3}+7T;\\ 3)\;& \Delta Z_T=117145+7{,}25T\ln T+1{,}68T^2\cdot10^{-3}-0{,}81T^{-1}\cdot10^5-73{,}5T;\\ 4)\;& \Delta Z_T=5730-2{,}48T\ln T+1{,}36T^2\cdot10^{-3}+21T;\\ 5)\;& \Delta Z_T=9000+7{,}52T\ln T+1{,}23T^2\cdot10^{-3}-52{,}1T. \end{aligned} \]

The results of the thermodynamic analysis are summarized in Table 2 and presented graphically in Fig. 3.

Table 2 (continued)

\(\Delta Z_T\), kcal/mol, at temperature, °K

Fig. 3. Dependence of \(\Delta Z_T\) of reactions in the system \(\mathrm{FeTiO_3—CaO}\) on temperature in the range 1073–1573°K: — reactions in a charge \(\mathrm{FeTiO_3:CaO}=1:1\); –·– reactions in a charge \(\mathrm{FeTiO_3:CaO}=1:2\); —x—x— reactions in a charge \(\mathrm{FeTiO_3:CaO}=1:3\).

Consideration of the data obtained shows that, for all ratios of the starting substances, beginning at \(1100^\circ\mathrm{C}\) the formation of all calcium titanates becomes thermodynamically probable.

For all ratios \(\mathrm{FeTiO_3:CaO}\), the formation of calcium monotitanate is more thermodynamically probable; and at ratios \(\mathrm{FeTiO_3:CaO}=1:2\) and \(1:3\), along with \(\mathrm{CaTiO_3}\), the formation of \(\mathrm{Ca_3Ti_2O_7}\) is also probable.

The sequence of formation of calcium titanates cannot be determined from thermodynamic data alone, since the occurrence of one or another reaction will depend not only on the magnitude of \(\Delta Z_T\), but also on kinetic factors, the principal one of which is the rate at which the given process takes place [9].

The study of the kinetics of the interaction of ilmenite with calcium carbonate is the objective of further investigations.

LITERATURE

1. B. A. Loshkarev. Refractories, No. 7, p. 310, 1950.
2. E. D. Ershov. Transactions of Giprocement, issue 1, p. 5, L., 1940.
3. A. S. Berezhnoy. Refractories, No. 8, p. 350, 1950.
4. P. S. Mamykin, B. A. Loshkarev. Refractories, No. 5, p. 215, 1950.
5. N. A. Toropov et al. Phase Diagrams of Silicate Systems. Izd. “Nauka,” M.—L., 1965.
6. E. A. Guber. Dissertation, Tomsk, 1965.
7. V. I. Babushkin, G. M. Matveev, O. P. Mchedlov-Petrosyan. Thermodynamics of Silicates. Publishing House for Construction Literature, M., 1965.
8. L. A. Zharkova. Journal of Physical Chemistry, vol. 36, 8, 1962.
9. Silicates and Oxides in High-Temperature Chemistry, ed. M. A. Matveev, M., 1963.
10. Coughanour L. W. R. S. Roth, V. A. de Prosse. Jour. Res. Nat. Bur. Stand., 52, No. 1, 37, 1954.