Entrained-flow chlorination of ilmenite to produce titanium tetrachloride and metallic iron
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I.
This overall reaction consists of two main reactions:
INTRODUCTION
T I T A N I U M is extracted from minerals, such as ilmenite, by chlorination with chlorine. In commercial operations, the relatively high iron content is converted to iron chloride, which constitutes a loss of chlorine values and creates a waste disposal problem. There are numerous methods proposed in the literature for recovering chlorine from iron chloride. However, none of these processes appear to be in large-scale operation, due apparently to operating difficulties. Normally, partial chlorination of ilmenite results in selective chlorination of the iron oxide content, leaving residual titanium oxide. Selective chlorination of ilmenite to yield titanium tetrachloride and metallic iron is possible under special conditions. Wilcox Iu showed that such a selective chlorination was possible at 1523 K or higher. Bonsack [2~indicated that reactors promoting concurrent flow of gas and solids, with no backmixing, are needed. Glaeser 13,41 indicated that FeCI2 or restricted ratios of FeCI2/C12 were required as the chlorinating agent. Othmer 151 used titanium tetrachloride as the chlorinating agent in a method that produced metallic iron and titanium dioxide or titanium tetrachloride from minerals such as ilmenite. In these processes, the key reaction that yields titanium tetrachloride and metallic iron is thought to be 2FeC12 (v) + TiO2 (s) + 2C = TiCI4 (v) + 2Fe(s) + 2CO
[1]
Under the reaction conditions for these processes, the stable species of Ti oxide is Ti203, so the key reaction is more correctly written:
2C12 + FeTiO3 + 2C = 0.5TIC14 + FeC12 + 0.5TIO2 + 2CO
[41
followed by FeC12 + 0.5TIO2 + C = 0.5TIC14 + Fe + CO
[5]
Reaction [4] must go essentially to completion before Reaction [5] can occur, because the chlorinating reactivity of FeC12 vapor depends on its dissociation: FeC12 (v) = Fe (s) + C12
[6]
Calculation of C12 partial pressures at 1473 to 1673 K from thermochemical data 161indicates that only very low pressures are possible, about 0.1 Pa at a total pressure of 10 s Pa. FeC12 is therefore an effective chlorinating agent only after the reaction of Clz in Reaction [3] or [4] is essentially complete. In the above reactions, FeTiO3 is used to illustrate the chemistry. The actual F e / T i ratio in natural ilmenites will show considerable variations. The extent of the FeC12 reaction to form metallic iron has been reported 12~3'41 for equilibrium conditions. The actual yields under more practical, time-restrictive conditions are lower, apparently because key Reaction [5] is relatively slow compared to Reaction [4]. This is not unexpected in view of the low partial pressure of C12 from dissociating FeC12 vapor. The purpose of this investigation was to determine the extent of the key reaction alone, that is, in the absence of added C12.
4FeC12 (v) + Ti203 (s) + 3C = 2TIC14 (v) + 4Fe (s) + 3CO
[2]
In a process using C12 as the sole chlorinating agent, t2j the C12/ilmenite ratio is controlled so that the overall reaction could be
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