Carbothermal Solid State Reduction of Manganese Ores : 1. Manganese Ore Characterisation

The South African Wessels and Australian Groote Eylandt manganese ores were characterized using XRD, optical, SEM and EPMA analyses. Two grades of Groote Eylandt ore were examined, one of them contained a high concentration of silica, 34.4 mass%. Wessels ore had high iron oxide and calcia content, and low concentration of silica. Major manganese-containing phases were bixbyite, braunite, manganite and hausmannite in Wessels ore, and pyrolusite in Groote Eylandt ore; both grades of Groote Eylandt ore contained silica inclusions. In the process of sintering in air and argon at 1000°C, MnO2 was reduced to Mn2O3 and Mn3O4, while in sintering in hydrogen manganese oxides were reduced to MnO and iron oxides to metallic iron. In the process of sintering of high-silica Groote Eylandt ore at 1200°C in inert atmosphere, tephroite was formed which was partially decomposed to rhodonite and MnO with increasing sintering time to 30 min. In the ore sintered at 1200°C in hydrogen for 1 h, major phases identified by XRD analysis were MnO, silica and tephroite.