Oxidation of Fe1−xS Pellet

The oxidation of iron sulfide pellet was studied at 773 to 973 K in a mixed O2–N2 gas stream. The composition of iron sulfide was Fe0.90S to Fe1.00S. The oxygen partial pressure in the gas stream was between 5.05×103 and 2.02×104 Pa. The results were compared with those in the oxidation of dense plates of iron sulfide reported in a previous paper. In the oxidation of the pellet of higher sulfur activity, the pellet mass was decreased from the start of oxidation accompanied by the evolution of SO2 gas. The rate of oxidation was controlled by gas film mass transfer in the initial stage of oxidation and by gas diffusion through the outer oxide layer of the pellet in the subsequent stage. In the oxidation of the pellet of lower sulfur activity, on the other hand, the pellet mass was increased in the initial stage of oxidation, which was followed by a decrease of the mass. The evolution of SO2 gas was observed from the start of oxidation. This observation is different from that in the oxidation of dense plates of iron sulfide: no SO2 gas was evolved during the period of mass increase. It was found that the preferential oxidation of iron which resulted in a mass increase took place in the inner core of the pellet simultaneously with the oxidation of sulfide of higher sulfur activity in the outer layer of the pellet which was accompanied by the evolution of SO2 gas. It was also found that the preferential oxidation of iron in the sulfide particles of which the pellet consisted took place in a very short time. The overall rate of oxidation of the pellet was analysed by a simplified model.