Pentetic acid/ammonia cooperatively stabilizes Cu(II) as an efficient oxidant for green thiosulfate leaching of gold

Abstract

Thiosulfate leaching is increasingly recognized as an environmentally sustainable alternative tocyanidation for extracting gold. One of the primary challenges in this field is identifying an effective stabilizer for the Cu(II) oxidant that simultaneously ensures efficient gold leaching and low thiosulfate consumption. This work introduces pentetic acid (DTPA) as a stabilizer for Cu(II) oxidant, forming a novel oxidation system based on the stable-chelated CuDTPA3− complex. Comparative leaching using (NH4)2S2O3 and Na2S2O3 highlight the beneficial role of ammonia (NH3) in enhancing the oxidation capability of the stable CuDTPA3− complex. The proposed mechanism suggests that NH3 contributes to the formation of a mixed [Cu(DTPA)(NH3)]3− complex with enhanced chemical reactivity. Additionally, DTPA is shown to effectively maintain the stability of the leaching system, thereby improving gold leaching, reducing thiosulfate consumption, and mitigating passivation. Through precise parameters control, a satisfactory gold leaching from a pretreated gold concentrate achieved a high efficiency of 97.8 %, with a low (NH4)2S2O3 consumption (8.7 kg/t-ore). Furthermore, the actual operation process can be facile designed by using more cost-effective leaching chemicals such as Na2S2O3 with a little addition of NH4OH or various ammonium salts, like (NH4)2SO4, CH3COONH4, and NH4Cl. This study provides valuable insights for advancing the commercial viability of environmentally friendly gold leaching processes.