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 to cyanidation 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.