Electrochemical reduction and recovery of trace gold(I) from environmentally friendly thiosulfate leaching solutions using carbon electrodes

Efficient recovery of Au(S₂O₃)₂³⁻ at low concentrations is a key challenge for the development of environmentally friendly, cyanide-free thiosulfate leaching methods in industry. In the study, carbon materials including activated carbon (AC), graphite, and graphene were used as electrodes for electrochemical reduction and recovery (electro reduction-recovery) of trace gold(I) from thiosulfate leaching solutions (Au(S₂O₃)₂³⁻). The results demonstrated that Au(S₂O₃)₂³⁻ could be efficiently recovered in the form of Au⁰ with nearly 100 % recovery from both simulated and actual gold ore leaching solutions, significantly simplifying traditional recovery and reduction processes. Even in the presence of impurities such as cations and S₂O₃²⁻, recovery remained high, around 90 %. Among the parameters studied, applied voltage was the most critical for optimizing recovery, as it enhanced ion migration and significantly improved gold reduction. The study investigated the relationship between the intrinsic properties of carbon materials and their electrochemical reduction and recovery capabilities. Rich porosity of carbon materials promoted interactions with Au(S₂O₃)₂³⁻, enhancing the electric double layer capacity, while π–π∗ satellite transitions played a dominant role in the charge transfer, thereby improving the reduction rate. This research offers new insights of the mechanisms behind the recovery of trace Au(S₂O₃)₂³⁻ from thiosulfate leaching solutions through carbon electrodes.