Phase Development in Carbothermal Reduction and Nitridation of Ilmenite Concentrates

Abstract

The phase development in the course of carbothermal reduction and nitridation of ilmentie concentrates and synthetic rutile was studied in temperature programmed reduction (623–1873 K) and isothermal reduction experiments. Ilmenites and synthetic rutile were reduced in a tube reactor with continuously flowing hydrogen-nitrogen mixture or pure nitrogen. 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. Pseudorutile was first converted to ilmenite and titania which occurred at temperatures below 623 K; iron oxides in ilmenite were quickly reduced to metallic iron. Titania was reduced to titanium suboxides and further to titanium oxycarbonitride. Reduction of ilmenites and synthetic rutile in hydrogen-nitrogen mixture was much faster than in pure nitrogen. The rate of conversion of titanium oxides to oxycarbonitride was affected by iron content in the ilmenites. The rate of reduction increased with increasing iron content in ilmenite (decreasing grade) when ilmenites were reduced in the hydrogen-nitrogen gas mixture, but decreased with decreasing ilmenite grade in reduction experiments in nitrogen; reduction in nitrogen was the fastest for synthetic rutile. The difference in the reduction behaviour was attributed to different chemical compositions and morphologies of ilmenites of different grades.

Keywords

• ilmenite
• reduction
• nitridation
• phase development