R-007

Wen Xuan

wen.xuan@univ-lorraine.fr

Benjamin Rotonnelli, Calogera Bertoloni, Stéphanie Michel, Sophie Legeai, François Lapicque

Université de Lorraine , France 

Electroleaching-electrodeposition of gold in choline chloride based deep eutectic solvents for gold recovery from electronic waste

The accumulating Electronic waste (WEEE) represents a serious environmental challenge while potentially serving as a valuable secondary resource for precious metals. This study focuses on developing electroleaching-electrodeposition (E-E) process in a single cell, with simultaneous dissolution of the precious metal-blend anode, and selectivity cathode electrodeposition of the targeted metal. Use of deep eutectic solvents (DES) instead of conventional cyanide-based liquors can improve the process efficiency and avoid environmental issues. 

The feasibility of recovering silver on silver electrode using this method when silver is the sole metal present in the system was recently demonstrated in a dedicated lab cell enabling E-E process, from ethaline 1 : 2 (choline chloride and ethylene glycol), propeline 1 : 3 (choline chloride and propylene glycol) DES. Here, the technical feasibility of extracting gold from gradually more complex anode and electrolytic solution through the E-E process was investigated, in view to production of pure gold with perfectly recyclable DES. A new cell was designed and manufactured by 3-D printing for the study of gold. During each step, physicochemical characterization of 10-30 µm thick deposit was performed to evaluate its weight, compactness and purity. Dedicated electrochemical measurements could indicate on the charge and mass transfer kinetics at the vicinity of the depositing surface.

First tests conducted with gold species at the electrode and in the solution, could validate the overall process: gold anode oxidizes exclusively to [AuCl2]- species, and both electrochemical reactions were achieved with current efficiency larger than 98%: high recyclability of the DES bath can thus be expected. Moreover, carbon-based materials e.g. fuel cell gas diffusion layers were shown effective alternatives as cathode substrate for Au electrodeposition, with comparable current efficiency at the two electrodes. The last part of the work focuses on a binary (Au-Ag) system at the anode and in the bath and the selectivity of the process where recovery of pure gold at the cathode is targeted. The presentation also discusses the efficiency of the process in the more real case depending on the nature/composition of the anode blend (pure alloy or sintered bimetallic phase), and on whether the run was conducted at a fixed current density or at a fixed potential of one of the two electrodes.