Sintering reactions of magnetite concentrates under various atmospheres

Sintering reactions of magnetite concentrates were studied under various atmospheres using a bench-scale infrared hearing furnace. The results show that the ability of magnetite to participate in reaction (reactivity) is dependent on gangue level and gangue minerals in the ore, and magnetite in easy-fusing ores has a high reactivity. The reactivity is remarkably improved by sintering in oxidising atmospheres without increasing temperature. Calcium ferrites can form prior to the oxidation of magnetite in atmospheres with very low oxygen partial pressure (P-O2) in the present of silica, the amount of calcium ferrites formed by this mechanism is negligible. The resulting sinters consist predominantly of magnetite and silicates. If cooled in high p(O2) after sintering in N-2, significant SFCA (silicoferrite of calcium and aluminium) forms and becomes the major bonding phase. The SFCA formation mechanism is likely to be via reactions of magnetite and melt in the presence of oxygen. This is considered to be the main route of SFCA formation in magnetite sintering. Most of the magnetite is oxidised to hematite in an oxidising atmosphere. Mineral formation in sintering of oxidised magnetite is similar to that observed for hematite in terms of dependencies on temperature, basicity and alumina content. Based on observations in this work, the following are suggested to develop SFCA and improve sinter quality in magnetite sintering: (1) increase the hematite level in ore blend; (2) develop magnetite oxidation; and (3) adopt low coke and oxidising atmosphere sintering practice.