Novel recovery of a low-concentration gold thiosulfate complex through electroreduction via a walnut shell charcoal electrode

Abstract

Low-concentration Au(S2O3)23− recovery is an urgent issue to facilitate the application of thiosulfate leaching instead of cyanide leaching in factories. Herein, this work presents a novel recovery of low-concentration Au(S2O3)23− combining adsorption and electrodeposition (electroreduction) to realize high Au(S2O3)23− recovery in the form of gold particles (Au0). Walnut shells were used as the raw material for the successful preparation of charcoal with porous structure and rich oxygen-containing functional groups. Walnut shell charcoal (WSC) as the electrode achieved efficient recovery of low-concentration Au(S2O3)23−. The recovery under low-concentration conditions was higher than 90%, with the highest reduction of 46.97 mg·g−1. Applying a suitable low voltage (0.8 V) facilitated low-concentration Au(S2O3)23− recovery, which was immensely improved than that without voltage. Au(S2O3)23− recovery performances under applied voltage via the WSC electrode were related to electrochemical abilities, including reaction intensity and charge transfer. More reactive sites containing suitable pores and oxygen functional groups were beneficial for the reduction reaction. This work offers a new way to recover low-concentration Au(S2O3)23− via cheap charcoal electrodes from solutions for application in the cyanide-free leaching method in industry.