Highly efficient electroextraction of gold and simultaneous iodine regeneration using ionic liquid 1-ethyl-3-methylimidazolium dicyanamide

Abstract

The iodination method is a cyanide-free and efficient gold-leaching process, but a large amount of electric energy is consumed for hydrogen evolution during the process of gold recovery by electrodeposition in the iodide/H2O system. Herein, [C2MIM][N(CN)2] ionic liquids were developed as electrolytes to overcome the limitations of water-based solvents for higher current efficiency by extending the electrochemical window. And the three-dimensional carbon felt with a high surface area and abundant active sites was selected as the cathode material to enhance the deposition rate. Cyclic voltammetry test demonstrated that both Au+ reduction and I- oxidation are irreversible processes controlled by diffusion with the diffusion coefficients of 1.48 × 10-7 cm2/s and 2.91 × 10-7 cm2/s at 20 °C, respectively. The optimal current efficiency (88.03%), specific energy consumption (216.37 kWh/t) and recovery of gold (95.77%), and iodine (85.75%) were obtained by regulating the electrodeposition parameters, including applied potential, temperature, and stirring speed. Moreover, the gold leaching and deposition efficiency were stable at approximately 93% and 95% with 0.2% iodine supplement for four cyclic leaching-electrodeposition. SEM-EDS, XRD, and XPS analysis showed the deposits on the carbon fibers had good uniformity, and the deposit composition contained Au0, Cu0, and CuO. [C2MIM][N(CN)2] ionic liquid is an attractive alternative to non-concentrated aqueous electrolytes for high-efficiency and low-power electrodeposition applications.