Recovery of Lead and Silver from Zinc Leaching Residue Using Methanesulfonic Acid

A solvometallurgical route for the recovery of lead and silver from the leaching residue of the zinc roast-leach-electrowin process was developed. Methanesulfonic acid was selected as the lixiviant because of the high solubility of lead and silver methanesulfonate salts. The direct leaching of the residue with methanesulfonic acid showed a high codissolution of gypsum and a low dissolution of lead (present as anglesite), requiring a high liquid-to-solid ratio. Two pretreatment processes were investigated to improve the leaching efficiency. First, the gypsum was selectively removed via Randall extraction using water as a solvent. Pure gypsum was obtained in this step, and the solvent could be reused multiple times. Second, the solubility of lead was increased by transforming the anglesite into cerussite via a carbonation reaction with sodium carbonate. When the carbonation reaction was performed before the removal of gypsum, a significant excess of sodium carbonate was required because the gypsum was also transformed into calcium carbonate. However, when the carbonation was done on the gypsum-free material, a stoichiometric amount of sodium carbonate was sufficient. The carbonation reaction drastically increased the lead dissolution, and the liquid-to-solid ratio requirements decreased. The leaching efficiency for both silver and lead using methanesulfonic acid as the lixiviant after Randall extraction and the carbonation reaction was around 80%.