Direct recovery of low concentrated Au(S₂O₃)₂^3- from the pregnant leaching solution via activated carbon electrode: from lab to pilot-scale experiment

Thiosulfate gold extraction technology has garnered significant attention for its eco-friendly nature and broad ore adaptability. However, the absence of efficient methods to recovery Au(S₂O₃)₂^3- from leaching solutions has hindered its industrial implementation. To address this challenge, this study is based on thiosulfate leaching solution from quartz-type gold ores, designed an activated carbon-modified titanium electrode (Ti@AC) with a porous structure on the surface. This electrode facilitates the direct reduction of low-concentration Au(S₂O₃)₂^3- to metallic gold (Au⁰) in solution, achieved a gold recovery of 99.58%, surpassing other recovery methods from leaching solution by 30-80%. After 10 consecutive 200 L pilot-scale tests, the Ti@AC electrode demonstrated remarkable stability, consistently maintaining a recovery above 98% and yielding a total of 20.23 g of gold. The porous architecture of the AC promotes the adsorption of low-concentration Au(S₂O₃)₂^3-, while its low charge transfer resistance facilitates the efficient conversion of Au(S₂O₃)₂^3- to Au⁰. Besides, the reduction reaction generates a concentration gradient near the cathode, promoting the diffusion of Au(S₂O₃)₂^3- toward the electrode and ensuring an efficient recovery process. This study provides a feasible strategy for the direct reduction of low-concentration precious metal ions to monomers with higher recovery and lower costs, which is broadly promising of industrial application.