Gold leaching from waste mobile phone PCBs in a solution mixture of sodium persulfate and potassium iodide

Gold is one of the most fascinating resources in the waste mobile phones’ printed circuit boards (WMPPCBs). In this study, a new process for recovering Au from WMPPCBs by the Na2S2O8-KI system was developed. This process comprises a two-stage leaching process to provide a separation of copper and gold from WMPPCBs. 98% Cu and 78% Fe were dissolved by the 1st base metals' leaching (H2SO4-H2O2 leaching) step. The leaching of gold from the solid reside of 2nd leaching step was performed to study the effect of Na2S2O8 concentration, KI concentration, temperature, and solid-liquid ratio in Na2S2O8-KI leaching system. The results showed that removing most of Cu greatly promoted the leaching efficiency of gold in Na2S2O8-KI leaching system. The mechanism of gold leaching was studied by the thermodynamic analysis. Leaching kinetics data showed that gold leaching followed an intermediate-controlled mechanism with Ea, 30.3 kJ mol−1. The best conditions for leaching of gold in Na2S2O8-KI system were determined to be 0.02 M Na2S2O8, 0.15 M KI, 40 ℃, a solid-liquid ratio of 1: 20 (g/mL), and a stirring speed of 200 rpm. Under the optimal leaching parameters, the efficiency of gold leaching from WMPPCBs attained 96% after 120 min. Due to the non-toxic and low-cost properties of Na2S2O8, the Na2S2O8-KI leaching process is more sustainable than conventional processes (cyanide leaching et al.).