Separation of polythionates and the gold thiosulfate complex in gold thiosulfate leach solutions by ion-interaction chromatography

Abstract

A method for the separation of the polythionates (S_xO₆²⁻, x= 3–5) in gold thiosulfate leach solutions using ion-interaction chromatography with conductivity and ultraviolet (UV) detection is described. Polythionates were eluted within 18 min using an eluent comprising an acetonitrile step gradient at 0.0 min from 15% v/v to 28% v/v, 3 mM TBAOH, and 2.5 mM sodium carbonate, operated using a Dionex NS1-5 μ column with guard. The developed method was capable of separating the gold thiosulfate complex ion in standard solutions, but quantification of this species in realistic leach solutions proved impractical due to a self-elution effect that caused the gold peak to be eluted as a broad band. Detection limits for polythionates using a 10 µL injection volume ranged between 1–6 mg L⁻¹ (5–23 µM) for conductivity and 0.8–13 mg L⁻¹ (4–68 µM) for UV detection, based on a signal-to-noise ratio of 2. Calibration was linear over the ranges 5–2000, 10-2000 and 25–2500 mg L⁻¹ for trithionate, tetrathionate and pentathionate, respectively. The technique was applied successfully to leach liquors containing 0.5 M ammonium thiosulfate, 2 M ammonia, 0.05 M copper sulfate and 20 % m/v gold ore.