Recovery of Gold and Silver from Secondary Sources of Electronic Waste Processing by Thiourea Leaching

Abstract

Fine materials, such as flue dust, generated during processing of electronic waste (e-waste) contain valuable metal resources, such as Au and Ag. However, recovery of valuable metals from this flue dust has not been extensively studied. In this study, a leaching process was investigated for effective recovery of Au and Ag from flue dust. In particular, thiourea was used as leaching reagent to replace cyanide, which has environmental problems. The effects of various parameters on the process, such as leaching time (1–10 h), thiourea concentration (20–60 g/L), and pulp density (20–100 g/L) as well as reaction temperature (20–60°C), were systematically examined. One- and two-step leaching methods were proposed to recover Au and Ag, respectively. Au and Ag leaching efficiencies of about 90% and 100% were obtained by one-step thiourea leaching. However, metals such as Fe and Al were also dissolved together. In the two-step process, Fe and Al were dissolved using H2SO4 as a first step, then Au and Ag were recovered using thiourea leaching. Using this two-step process, Au and Ag were dissolved at higher purity than when using the one-step leaching process, achieving leaching efficiencies of about 98% and 100%, respectively. This investigation will lead to a cost-effective method for recovering precious metals from secondary waste.