TIN RECOVERY FROM AN ELECTROPLATING SLUDGE

Tin electroplating from a fluoroborate electrolyte produces sludge containing approximately 50% tin. It can be extracted by leaching the sludge with concentrated hydrochloric acid at room temperature for one month or by boiling in 10% HCl solution for two hours. Electrowinning from H2SnCl6 solution with a steel cathode and graphite anodes permits recovery of tin with 93% efficiency at tin concentrations in the electrolyte exceeding 50 g/l and a current density of 5 A/dm2. The cell is covered with a box with air passing through two washers filled with 15-20% NaOH solution. Chlorine gas evolved at the anodes is adsorbed in washers; sodium hypochlorite, of more than 10% strength in solution, is yielded as a byproduct, with 80% efficiency.