Phase Development in Carbothermal Reduction of Ilmenite Concentrates and Synthetic Rutile

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The phase development in the course of carbothermal reduction of ilmentie concentrates and synthetic rutile was studied in temperature programmed reduction (350–1600°C) and isothermal reduction at 1100°C in hydrogen and 1300°C in argon and helium. Ilmenites and synthetic rutile were reduced in a tube reactor with continuously flowing gas. The rate and extent of reduction were monitored by online off-gas analysis. Samples reduced to different extent were subjected to XRD and SEM/BSE analyses. Pseudorutile and ilmenite were the main phases in ilmenite concentrates; rutile was the main phase in synthetic rutile. The phase changes in the course of reduction followed the same sequence in both hydrogen and inert gases. Pseudorutile was converted to ilmenite and titania; iron oxides in ilmenite were quickly reduced to metallic iron. Titania was reduced to titanium suboxides and further to titanium oxycarbide. Reduction of ilmenites and synthetic rutile in hydrogen was much faster than in inert atmosphere. The rate of conversion of titanium oxides to oxycarbide was affected by iron content in the ilmenites. The reduction of lower grade ilmenite with high iron content was faster in hydrogen; but slower in an inert gas. The latter was attributed to the higher porosity of highly weathered ilmenite and synthetic rutile.