Refining of Secondary Pb with Retention of Sn Using Al and Ca Additions

Abstract

Lead grid from spent lead-acid batteries contains significant amounts of tin and antimony. In classical pyro-refining processes of lead, tin oxidizes and is transferred to dross, making its recovery problematic and expensive. This paper presents an innovative method of pyro-refining lead using metallic aluminum and calcium to purify the lead from contaminants while retaining a higher amount of tin than in the traditional process. The changes in the chemical composition of an impure lead alloy containing tin, under the influence of refining by adding Al and/or Ca, are discussed based on laboratory-scale studies. Microanalysis of the metallic dross formed during the process was conducted. Analyses of the metallic dross microstructures showed that lead impurities, such as Sb, As, Cu, Se, and Te, tend to accumulate in areas containing Al or Ca. The amount and form of dross produced in industrial practice indicate that its removal would be challenging. Therefore, in the second part of the study, the metallic dross was subjected to a reduction process, and the resulting products were analyzed for their chemical and phase composition. The analyses indicate that the degree of impurities return to the lead during reduction varied significantly depending on the method used.