RI 8602 Electrolytic Method for Recovery of Lead From Scrap Batteries

Bench-scale research at the Bureau of Mines has resulted in the successful development of a combination electrorefining-electrowinning method for recycling all the lead in scrap batteries. The method reduces energy consumption and eliminates toxic emissions, in contrast to present pyrometallurgical smelting, and the lead produced is pure enough for use in maintenance-free batteries. Anodes cast from molten lead scrap were electrorefined in 1-and 2-liter plastic cells using an electrolyte composition of 70 g/l Pb and 90 g/l free H2SiF6 (fluosilicic acid). Both reagent-grade and waste H2SiF6 were used. Cathode starting sheets were made from refined lead. Aloes, and later bone gelatin, and calcium lignin sulfonate addition agents were employed. The sludge remaining after separation of the lead metal was treated in a two-step leaching operation to solubilize the lead for recovery by electrowinning. Conditions for electrowinning were essentially the same as for electro-refining, except that insoluble Pb02-Ti (lead dioxide-coated titanium) anodes were used. The best results for both electrorefining and electrowinning were obtained with a current density of 170 amp/m2 and a cell temperature of 25° to 35° C. Cathode purity ranged from about 99.9 to 99.99+ pct Pb. Maximum energy consumption after 3 days, for electrorefining and electrowinning, was 90 and 700 kwhr per metric ton of refined lead, respectively.