The quantification of thiosulfate and polythionates in gold leach solutions and on anion exchange resins

Analytical procedures based on ion chromatography utilising an anion exchange column and UV detection are described for the quantification of thiosulfate, polythionates and gold thiosulfate both in leach solutions and adsorbed on anion exchange resins. The analysis of resins involves a two step perchlorate strip, and since perchlorate is used as the chromatography eluent, the high background concentration in the sample has little effect on the retention. Results are reported for the analysis of gold thiosulfate leach solutions and it is shown that tetrathionate and pentathionate are the dominant reaction products from thiosulfate oxidation at pH 8.5 and 9, whilst trithionate and sulfate are formed at pH 10.4. An increase in thiosulfate consumption when increasing pH from 8.5 to 9 is attributed to the increase in the rate of copper(I) oxidation with increasing ammonia concentration. However, the rate of thiosulfate consumption is higher at pH 9.0 than pH 10.4, and this is explained in terms of the differing reaction products. The adsorption of thiosulfate, polythionates and gold thiosulfate onto anion exchange resins is also discussed with reference to the quantification of the equilibrium solution and resin concentration of each species. Isotherms for gold on resin vs. gold in solution are reported for solutions of various polythionate concentrations.