Green hydrometallurgical extraction of metallic lead from spent lead paste in the methanesulfonic acid system

Abstract

As the mainstream process for recycling waste lead-acid battery paste to produce metallic lead ingots, pyrometallurgical smelting generally suffers from disadvantages such as high energy consumption, lead vapor and sulfur dioxide emissions. Hydrometallurgical extraction has received widespread attention because of its energy-saving and environmentally-friendly features. An innovative and efficient process for the hydrometallurgical recovery of lead paste was presented in this paper. In order to significantly improve the leaching efficiency of lead, PbSO4 in the lead paste was firstly converted into acid-soluble Pb3(CO3)2(OH)2 or NaPb2(CO3)2OH in Na2CO3 solution. At the same time, the insoluble PbO2 was reduced to PbO by the addition of Na2SO3. The pretreated product was then leached in MSA solution to obtain the lead-containing leachate, which was finally electrodeposited to produce lead deposits and to regenerate MSA. Under the optimized conditions, a dense and flat lead plate (purity greater than 99.99 %) could be obtained and the total lead recovery ratio in the whole process can reach 95.28 %. The cathode current efficiency and specific energy consumption in the lead electrodeposition procedure were 99.31 % and 598.91 kWh/t Pb, respectively. The electrolyte waste could be returned to the leaching process as the leaching agent. In contrast to the traditional fluorosilicate/fluoroborate and chloride systems, the environmentally-friendly MSA system with high lead solubility and low volatility, has promising applications in the field of lead hydrometallurgy.