Sequential and Selective Separation of Tin and Lead from Solder of Waste Printed Circuit Boards: Electrochemical Study

Separation of tin and lead from solder scrap material collected from the dismantling of printed circuit boards was studied with the aim of recycling the tin and isolating the lead. The study focussed on scrap solder recovered from waste printed circuit boards with a metal content of 62.1% Sn, 28.6% Pb, with 9.3% other metals as impurities. Separation of Sn was achieved through electrorefining, for which the solder was cast into an anode electrode, while a titanium cathode was used to plate the dissolved Sn. The effect of current density, Sn electrolyte concentration, HCl concentration, electrode spacing, and temperature on the voltage required for electrorefining, morphology, and mass of refined tin was studied. A bright, feather-like Sn deposit was obtained at optimum conditions, which were achieved at a current density of 150 A/m 2 , electrolyte concentration of 5 g/L Sn 2+ , HCl concentration of 7.3 g/L, electrode spacing of 1.5–2.0 cm, and a temperature of 25 °C with a current efficiency of > 97%. After electrorefining, the black film remaining on the anode was scraped off, characterized by EDS, and found to be lead oxide (PbO). Removal of the PbO film with 10% HNO 3 and HCl were attempted, with HNO 3 performing better. The dissolved lead could be recovered as PbCl 2 from either solution.