High purity metal lead recovery from zinc direct leaching residue via chloride leaching and direct electrolysis

Abstract

Clean and efficient recovery of lead from zinc direct leaching residue has good environmental and economic benefits. The paper firstly developed a clean and efficient electrolysis process to prepare metal lead from solid lead chloride obtained by leaching zinc direct leaching residue with brine. The solid lead chloride pellets could be well converted into metal lead by direct electrolysis in NH3-NH4Cl electrolyte at constant voltage. Metal lead with 99.1% lead purity was finally obtained by constant voltage electrolysis, and the corresponding extent of lead conversion, current efficiency, and specific energy consumption were 99.32%, 96.75% and 0.575 kW·h/kg respectively. Furthermore, the main technical parameters were also determined, such as a voltage of 2.15 V, working temperature of 45 °C, NH4Cl concentration of 2.0 mol/L, pellet thickness of 1.5 mm and time of 70 min. In addition, the mechanism of the direct electrolysis from solid lead chloride to metal lead in NH3-NH4Cl electrolyte was also proposed, which indicated that the rapid diffusion of electrolyte formed a good conductive network was critical in promoting the direct electrolysis of solid lead chloride. Moreover, the process proposed gives a feasible alternative to recycle lead from zinc direct leaching residue with an environment-friendly method.