Ion exchange adsorption and elution for recovering gold thiosulfate from leach solutions

Abstract

A new elution process for recovering gold thiosulfate from resins is described, and is based on the concept of synergistic ion exchange. In the presence of sulfite, Au(S 2O 3) 2 3− is converted to Au(S 2O 3)(SO 3) 3−, which has a reduced affinity for strong anion exchange resins and is shown to be readily eluted by weaker eluants, such as chloride. Chloride has several advantages over other systems: it is significantly cheaper and more stable than trithionate, and the return of chloride loaded resin to the adsorption circuit is less problematic than nitrate. Using the proposed chloride + sulfite system, the majority of the gold is stripped within 2 BV of elution, and the gold can be readily recovered from the concentrated eluate using electrowinning. The copper is pre-eluted using ammonium thiosulfate, with stripping of 99.7% of the copper, and only 2.7% of the gold. The new elution process was operated in closed loop with a continuous 7 stage adsorption mini-rig, and a solution gold grade of < 0.02 mg L − 1 is obtained within 6 tanks. The composite solution tail over 24 h is 0.005 mg L − 1 gold, indicating that the elution process produces a resin which is ideally suited for recycling without regeneration.