Reductive leaching of indium and zinc from zinc neutral leach residue with sulphuric acid and sulphur dioxide

Indium and zinc extractions from zinc neutral leach residue were investigated with sulphuric acid and sulphur dioxide. Sulphur dioxide maintained a low concentration of Fe3+ in the solution and promoted the decomposition of zinc ferrite. More zinc, indium, and iron dissolve into the solution, while copper co-precipitates with arsenic and sulphur into the residue. The optimal reductive leaching conditions were determined as 120 g/L H2SO4, 200 kPa sulphur dioxide partial pressure, a liquid-to-solid ratio of 8 mL/g and a stirring speed of 500 r/min at 105 degrees C for 4 h. Extractions of 95.24% of zinc, 98.66% of iron, 95.04% of indium and 0.036% of copper were achieved. Copper in final residue exist as sulphides and can be recovered by subsequent oxygen pressure leaching. Selective recovery of valuable metals from zinc neutral leach residue is realised.