Efficient and stable leaching of gold in a novel ethydiaminedhephen acetic-thiosulfate system

Gold thiosulfate leaching is renowned for its non-toxic and high leaching efficiency. However, in traditional thiosulfate leaching systems, the presence of a high mixed potential and oxidizing metal ions in the solution environment leads to the consumption of thiosulfate through oxidation and causes passivation of the gold surface. Here, we proposed a novel thiosulfate leaching system mainly using non-toxic copper-ethydiaminedhephen acetic (EDDHA) replacing the conventional copper-ammonia. In this system, the gold leaching process mainly catalyzed by the stable Cu-EDDHA complex ion (as oxidizing agent analyzed by UV–vis spectrophotometer). The complexation of Cu(II) attributed to EDDHA reduces the mixed potential in the leaching process. The coordination also prevents the oxidation of thiosulfate by free copper ions. Accordingly, thiosulfate consumption during leaching is minimized, as it mitigates oxidation and self-decomposition. Besides, Raman and XPS spectrum demonstrate that introduce of EDDHA into the thiosulfate system can effectively eliminate the harmful surface passivation of gold, which enhance the gold leaching efficiency. In addition, by fulfilling a set of conditions, a gold extraction of 82.84 % can be attained in new system compared with 56.02 % for conventional cyanide leaching. Further, adding EDDHA to the thiosulfate leach reduced the reagent consumption from 103.19 kg/t to 10.54 kg/t. The results are benefits to the development and utilization of thiosulfate gold leaching.