Ion Exchange Process for Gold Recovery
Ion exchange technology adapted to the treatment of aurocyanide solutions comprises three steps: loading, elution, and recovery. Once elution is performed, the obtained solution can be treated by electrowinning. Electrolytic cells have steel wool as cathodes and stainless steel as anodes. Steel wool is smelted and gold is obtained like bullion. Some typical parameters of electrowinning are current, 0.3-0.8 amp/dm2, 0.4-0.8 kw-hr/oz. The final electrolyte is recycled to the elution step.
The adaptation of ion exchange resins and techniques to the recovery process for gold has been one of the most significant developments in process technology. Applications of ion exchange resins is based on the existence of anionic complexes of gold in cyanide solutions, which under proper conditions are selectively adsorbed from a leach liquor by suitable synthetic resins. Reversing the exchange reaction with suitable eluting reagents then produces a purified and concentrated gold solution ideally suited for the direct production of relatively high grade gold product.
Initial ion exchange installations were similar to those used in water treatment, with gold the gold bearing solutions passed through columns containing fixed beds of resin until breakthrough, i.e. until a specified low concentration of gold was reached in the discharge solution. Use of this unit in series improved the extraction of the gold from solutions and increased the working capacity of the resin. Further process improvements to fit the particular requirement of the gold standard recovery processes resulted in the development of special resins and in the use of moving beds column ion exchange. Other developments in the industry included the Resin-in-Pulp process for treatment of feed slurries from which separation of clear liquor was difficult or non-economical. Suspension of the resin directly in an agitated slurry with separation and countercurrent movement of the resin and slurry through multiple stages of a continuous operation was a concurrent development.