Removal of harmful elements and sodium carbonate reinforced carbothermic reduction of siderite ore with high phosphorus and sulphur content

Abstract

Siderite ore from Huimin, Yunnan, China is characterised by high phosphorus and sulphur content. In this study, the beneficiation of this iron ore by carbothermic reduction and by a combined dressing-metallurgy process that included reverse flotation, sodium carbonate reinforced carbothermic reduction and magnetic separation were investigated. In the carbothermic reduction process, pyrite was converted to iron sulphide (FeS) and phosphorus compounds remained as fluorapatite in the gangue phases. These compounds lead to excess phosphorus and sulphur concentrations in the iron concentrate. Therefore, the removal of the phosphorus and sulphur from raw ore by reverse flotation prior to the reduction process was necessary. The use of Na₂CO₃ as a pulp pH modifier proved important for the non-synchronous removal of sulphur and phosphorus. Reduced ore produced without a Na₂CO₃ additive to the reduction process had iron particulates of small size (<10 μm) and an abundance of fayalite components. The formation of fayalite in the reduction process appeared to be the main hindrance to the reduction of siderite. When Na₂CO₃ was added to the reduction process to ore mass ratio of 5% after sulphur and phosphorus removal, the reduction of siderite was reinforced. After the grinding and magnetic separation process, an iron concentrate with 65⋅85% Fe was obtained. The iron concentrate also had a decreased content of phosphorus (0⋅21%) and sulphur (0⋅28%) and can be served as raw material in ironmaking.