Direct recovery of low-concentration \bf Au(\bf S_\bf 2\bf O_\bf 3)_\bf 2^\bf 3- from pregnant leach solution using an activated carbon-coated titanium electrode

Thiosulfate gold extraction technology has gained considerable interest owing to its environmental compatibility and broad applicability to diverse ore types. However, the lack of efficient methods to recover \mathrmAu(\mathrmS_2\mathrmO_3)_2^3- from leaching solutions has hindered its industrial implementation. To address this challenge, this study used a thiosulfate leaching solution from quartz-type gold ores to design an activated carbon-coated titanium electrode (Ti@AC) with a porous surface structure. This electrode facilitated the direct reduction of low-concentration \mathrmAu(\mathrmS_2\mathrmO_3)_2^3- to metallic gold (Au⁰) in solution, achieving a gold recovery of 99.58%, surpassing other recovery methods from the leaching solution by 30%‒80%. After ten consecutive 200 L pilot-scale tests, the Ti@AC electrode demonstrated remarkable stability, consistently maintaining a recovery >98% and yielding 20.23 g of gold. The porous architecture of the activated carbon (AC) promoted the adsorption of low-concentration \mathrmAu(\mathrmS_2\mathrmO_3)_2^3- , while its low charge transfer resistance facilitated the efficient conversion of \mathrmAu(\mathrmS_2\mathrmO_3)_2^3- to Au⁰. Moreover, the reduction reaction generated a concentration gradient near the cathode, promoting the diffusion of \mathrmAu(\mathrmS_2\mathrmO_3)_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 high recovery and low costs, which is promising for industrial applications.