Selective extraction and recovery of tin from hazardous zinc-leaching residue by oxalic acid/sulfuric acid mixture leaching and hydrolytic precipitation

Zinc-leaching residue (ZLR) with 0.46% Sn and 54% Pb brings potential threats to environment but is worthy to recover valuable metals. Reduction of Sn(IV) to Sn(II) is critical for tin extraction. In this work, selective extraction and recovery of tin from ZLR via oxalic acid/sulfuric acid leaching and hydrolytic precipitation was proposed. Various reductants were attempted, and the oxalic acid shows superior tin leaching efficiency. The effects of reduction leaching and hydrolysis parameters on the separation of Sn and Pb were systematically investigated. After leaching by 24 g/L oxalic acid in 0.50 mol/L H2SO4 at 60 °C for 30 min with L/S ratio of 10 mL/g and stirring speed of 400 r/min, 90.5% Sn is leached into the solution, and 99.8% Pb is simultaneously concentrated in the leaching residue. In the hydrolysis process, tin sediment with recovery of 93.8% and content of 46.4% was obtained. The as-prepared tin and lead products can directly act as concentrates for the tin and lead smelting. The oxalic acid reduction leaching mechanism of tin was also discussed. Based on the reduction leaching behaviors of tin from ZLR, the possible Sn leaching enhancement via oxalic acid addition in the existing industrial zinc-leaching process was proposed in this work.