Pressure leaching technique for manganese smelter dust

Pressure leaching of manganese smelter dust with air as pressurized gas in a sulfuric acid medium was investigated. Optimum operating parameters were established as follows: liquid-to-solid ratio (mL/g), 5:1; initial sulfuric acid concentration, 120 g/L; leaching temperature, 120 °C; air pressure, 0.8 MPa; ore ratio (manganese smelter dust amount/pyrite amount), 1:0.5; leaching time, 2 h; and agitation speed, 500 r/min. Extraction rates of manganese and iron were obtained at 96.1% and 7%, respectively, under these conditions; and residual percentage of final acid was about 34.9%. Manganese can be effectively separated from impurities, such as iron, through leaching process. Leaching efficiency of manganese increased from 72.9% to 96.1%, whereas that of iron and the residual percentage of final acid both decreased with increase in leaching time from 40 min to 120 min. Pyrite was coated by elemental sulfur when temperature was higher than 119 °C, resulting in its inability to act as a reductant and to react with manganese dioxide. Therefore, leaching temperature must be lower than 120 °C. Pressure leaching technique for manganese smelter dust was proven to be effective and reliable.