Recovery of Gold from Thiosulfate Solutions and Pulps with Anion- Exchange Resins

With growing environmental and occupational safety concerns over the use of cyanide in gold processing, more acceptable alternatives are receiving increased interest. The most promising of the possible alternatives is thiosulfate. However, as activated carbon is not an effective substrate for the adsorption of the gold thiosulfate complex, the thiosulfate process lacks a proven in-pulp method for recovering dissolved gold. Anion exchange resins offer a possible route for in-pulp recovery. This thesis describes the operation of a small-scale resin-in-pulp plant which demonstrated that gold could be recovered from a leach pulp to yield loadings of gold up to 6000 mg L⁻¹, while keeping copper loadings below 100 mg L⁻¹. Under ideal conditions, gold concentration in barren pulp could contain less than 0.01 mg L⁻¹. Loaded copper was displaced by gold, resulting in a significant drop in copper levels on the resin. It was found that some adsorbed gold was also recovered through the anion exchange resins. Gold was effectively eluted with a nitrate solution, allowing for recycling of the resin without regeneration. Electrochemical studies indicated that the gold thiosulfate complex could be reduced, thus conventional electrowinning may be applied for gold recovery from the eluant.