Selective silver electroseparation from ammoniacal thiosulfate leaching solutions using a rotating cylinder electrode reactor (RCE)

A systematic electrochemical study at controlled potential, using a rotating cylinder electrode reactor, was carried out on a synthetic solution with composition 0.2mol/L Na2S2O3, 0.05mol/L CuSO4, 0.025mol/L EDTA, 0.6 mo/L NH3, 1 × 10− 3mol/L AgNO3, which simulates actual leaching solution, to determine the conditions which permit the selective silver electroseparation with a minimum interference from the copper ions. The presence of 10 ppm of gold (5 × 10− 4M Au(I)) was found to enhance the gold–silver alloy deposition, with negligible effect on the copper ions. Those results were compared to that obtained with solutions originating from a previously characterized sulfide concentrate leach, in order to determine the influence of other impurities present in the pregnant solution, on the selective silver electrodeposition, obtaining averaging current efficiencies of 80%, with 90% of silver in the formed deposit and less than 5% of both, copper and lead, with only minor quantities of iron and zinc. Additionally, it was shown that the resulting solution could be recycled back to the leach stage, obtaining similar performances to those produced by the fresh solution, implying that it was not significantly altered in its composition, by the electroseparation process.