Behavior of gold and non-ferrous metals during low-temperature chlorination roasting of e-waste

Abstract

Based on a literature review, the relevance and necessity of processing e‑waste are shown. Pyro-, hydro- and biometallurgical methods for processing e‑waste are briefly described, and the advantages and disadvantages of existing technologies are compared. The efficiency and the environmental and health impacts of various technologies are analyzed.

The low-temperature chlorination technology applied to e‑waste processing is given a thermodynamic interpretation to obtain additional information necessary for better understanding of the behavior of gold and other non-ferrous metals with low metal content. The mechanism of the interaction between e‑waste elements and gaseous chlorine during low-temperature roasting was studied. The behavior of metals at low temperatures of chlorination of e‑waste (below 673 K) was assessed from the changes in the thermodynamic quantities of the system. Thermodynamic calculations were conducted to determine the Gibbs free energy (\(\Updelta {G}_{T}^{0}\)) of the reactions between e‑waste elements and gaseous chlorine at various temperatures. Based on the thermodynamic calculations of the reactions of precious (gold, silver, platinum, palladium) and other non-ferrous metals (Cu, Pb, Zn) with gaseous chlorine at low chlorination temperatures of 323–673 K, it was established that it is possible to selectively recover gold as sublimates Au₂Cl_6(g) and to produce a solid-phase cinder containing solid chlorides of precious and non-ferrous metals. The low-temperature chlorination roasting of e‑waste is a good prerequisite for the integrated recovery of gold and other precious and non-ferrous metals with high efficiency. The obtained results will be used for the selection, justification, and science-based design of innovative technology for processing e‑waste, using not only gaseous chlorine, but also solid chlorine-containing reagents (CaCl₂, NaCl).