Use of polyethylenimine functionalised magnetic nanoparticles for gold thiosulfate recovery

Abstract The use of calcium thiosulfate (CaS2O3) as an alternative lixiviant to cyanide to treat double refractory gold ores has become an industrial reality. In this study, a novel adsorbent, polyethylenimine coated iron oxide magnetic nanoparticles (PEI-MNPs), was evaluated for the adsorption of gold from thiosulfate leaching systems that contain gold, copper and calcium thiosulfate. Particles were characterised in terms of their size and morphology, zeta potential, crystalline structure, surface properties, functional groups, magnetic properties and thermal degradation properties. The effect of nanoparticle dosage, thiosulfate concentration, copper concentration, solution pH and solution temperature on gold loading in synthetic leaching solutions was examined. In addition, adsorption kinetics and adsorption isotherms were investigated. PEI-MNPs demonstrated a positive surface charge up to a pH of 11, which facilitated electrostatic attraction of anionic gold thiosulfate complex. A higher nanoparticle dosage, lower free thiosulfate concentrations and lower temperatures favoured gold adsorption, while copper concentration and solution pH did not show a considerable effect. Gold adsorption kinetics were fast, irrespective of the solution content and reached equilibrium in less than 30 min. The adsorption isotherm data could be fitted with both the Langmuir and the Freundlich isotherm models. The adsorbent was able to be reused after a selective metal elution process.