Recyclable Recovery of Lead from Zinc Hydrometallurgy Residue: By NH4Cl-MgCl2 Leaching and Novel Cyclone-Electrowinning

Lead sulfate residue, generated from the leaching of low-grade zinc oxide derived from rotary kilns with a lead content of 35–45%, is toxic and hazardous. Nonetheless, it also constitutes a valuable secondary lead resource. In this study, a novel, recyclable method was employed to recover lead. The results of the Response Surface analysis demonstrated that the leaching rate of lead achieved 97% when the main leaching reagent NH4Cl was 200 g L–1, the assistant leaching reagent MgCl2 was 140 g L–1 along with the leaching time of 1.5 h and temperature of 90 °C by utilizing CaCl2 as a sulfate radical precipitator and fixing a liquid–solid ratio of 20:1. Lead powder was obtained by utilizing a novel upside-down cyclone-electrowinning method without harmful gas emission. The current density in relation to current efficiency (CE) and power consumption was also investigated. The electrolyte could be recycled back for leaching after ammonia supplementation, thus forming a circular procedure, providing an effective and environmentally friendly method for disposing the lead sulfate residue.