High-Zinc Recovery from Residues by Sulfate Roasting and Water Leaching

An integrated process for the recovery of zinc that is generated from zinc hydrometallurgy in residues was developed. A mixture of residue and ferric sulfate was first roasted to transform the various forms of zinc in the residue, such as ferrite, oxide, sulfide, and silicate, into zinc sulfate. Next, water leaching was conducted to extract the zinc while the iron remained in the residue as ferric oxide. The effects of the roasting and leaching parameters on zinc recovery were investigated. A maximum zinc recovery rate of 90.9% was achieved for a mixture with a ferric sulfate/residue weight ratio of 0.05 when roasting at 640A degrees C for 30 min before leaching with water at room temperature for 20 min using a liquid/solid ratio of 10. Only 0.13% of the iron was dissolved in the water. Thus, the leaching liquor could be directly returned for zinc smelting.