Carbothermal solid state reduction of manganese oxide and ores in different gas atmospheres

摘要

The aim of the project was to establish rate and mechanisms of solid state reduction of manganese ores. The project studied carbothermal reduction of manganese oxide MnO, two Groote Eylandt (Australian) and Wessels (South African) manganese ores in hydrogen, helium and argon atmospheres at temperatures up to 1400C for MnO and 1200C for manganese ores. Experiments were conducted in the fixed bed reactor with on-line off-gas analysis. The major findings are as follows.•Rate and degree of reduction of MnO and ores increased with increasing temperature. •Reduction of MnO and manganese ores at temperatures up to 1200C was faster in helium than in argon, and much faster in hydrogen than in helium. The difference in MnO reduction in hydrogen and helium decreased with increasing temperature to 1400C.•Addition of up to 7 vol% of carbon monoxide to hydrogen had no effect on MnO reduction at 1200C.•In the process of carbothermal reduction of ores in hydrogen at 1200C, silica was reduced.•Reduction of both GE ores was slower than of Wessels ore. This was attributed to high content of iron oxide in the Wessels ore.•Carbon content in the graphite-ore mixture had a strong effect on phases formed in the process of reduction; thus, in the reduction of Wessels ore with 12-16 wt% C, a-Mn and Mn23C6 were formed; when carbon content was above 20 wt%, oxides were reduced to carbide (Mn,Fe)7C3.•Kinetic analysis showed that mass transfer of intermediate CO2 from oxide to graphite in carbothermal reduction in inert atmosphere was a contributing factor in the rate control.•High rate of reduction of manganese oxide in hydrogen was attributed to formation of methane which facilitated mass transfer of carbon from graphite to oxide. Hydrogen was also directly involved in reduction of manganese ore reducing iron oxides to metallic iron and higher manganese oxides to MnO.Reduction of Wessels and Groote Eyland Premium Fines ores in the solid state is feasible at temperatures up to 1200C; while temperature for solid state reduction of Groote Eyland Premium Sands is limited by 1100C.