Sintering reactions of magnetite concentrates were studied under vario
us atmospheres using a bench-scale infrared hearing furnace. The resul
ts show that the ability of magnetite to participate in reaction (reac
tivity) is dependent on gangue level and gangue minerals in the ore, a
nd 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 oxidati
on 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 predomi
nantly of magnetite and silicates. If cooled in high p(O2) after sinte
ring in N-2, significant SFCA (silicoferrite of calcium and aluminium)
forms and becomes the major bonding phase. The SFCA formation mechani
sm 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 depend
encies on temperature, basicity and alumina content. Based on observat
ions in this work, the following are suggested to develop SFCA and imp
rove 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.