Isothermal reduction and nitridation kinetics of ilmenite concentrate in ammonia gas.

• Isothermal kinetics of reduction and nitridation of ilmenite concentrate by ammonia gas is studied. • Both model–free and model–fitting methods are used to compare the isothermal kinetics. • The mechanism function and apparent activation energy of the reduction and nitridation stages are obtained. • The mechanism on reduction and nitridation is discussed. Low-temperature chlorination is considered a suitable process for ilmenite containing high contents of MgO and CaO. However, reduction carbonization or nitridation is essential to convert titanium oxide to carbide or nitride, which can be enriched by magnetic separation. In this paper, the isothermal reduction–nitridation kinetics of Panzhihua ilmenite concentrate in an ammonia atmosphere was investigated. Both model–free and model–fitting methods were used to compare the isothermal kinetics. The reaction process can be divided into two successive stages: the reduction reaction and the nitridation reaction. The average apparent activation energy for the reduction reaction was 139.63 kJ/mol, obtained by the model–free method. The reduction process can also be subdivided into two stages by the model–fitting method. The chemical reaction (G(α) = 1–(1– α)1/3 = kt) and three–dimensional diffusion (G (α) = [1–(1– α)1/3]2 = kt) were identified as the mechanism function for the reduction process. The activation energies of these two stages were 121.73 kJ/mol and 141.40 kJ/mol, respectively. The function G(α) = 1–(1– α)1/3 = kt , which also corresponds to the chemical reaction mechanism (R 3), exhibited the best fit for the nitridation stage. The corresponding activation energy was 32.10 kJ/mol. Metallic iron and Ti 3 O 5 were formed in the reduction stage, while Ti 3 O 5 was then transformed to Ti(N,O) in the nitridation stage. [ABSTRACT FROM AUTHOR]