Recovery of precious metals from electronic scrap by hydrometallurgical processing routes

Abstract

Although copper is the principal metal in most electronic scrap, printed circuit boards in mobile phones also contain a significant amount of silver, gold and palladium. A bench-scale extraction study was carried out on the applicability of economically feasible hydrometallurgical processing routes to recover these precious metals. The starting material contained 27.37% copper, 0.52% silver, 0.06% gold and 0.04% palladium. In a first step, the following leaching solutions were applied: an oxidative sulfuric acid leach to dissolve copper and part of the silver; an oxidative chloride leach to dissolve palladium and copper; and cyanidation to recover the gold, silver, palladium and a small amount of the copper. A thiourea leach, as an alternative to cyanidation, was also investigated but did not give a sufficiently high yield. To recover the metals from each leaching solution, the following methods were evaluated: cementation, precipitation, liquid/solid ion exchange and adsorption on activated carbon. Precipitation with NaCl was preferred to recuperate silver from the sulfate medium; palladium was extracted from the chloride solution by cementation on aluminum; and gold, silver and palladium were recovered from the cyanide solution by adsorption on activated carbon. The optimized flowsheet pe united the recovery of 93% of the silver, 95% of the gold and 99% of the palladium.