Alternative copper(II) catalysts for gold leaching: Use of multidentate ligands to control thiosulfate oxidation

Tiffany Brown, Adam Fischmann, Leone Spiccia*, D. C. McPhail

*Corresponding author for this work

    Research output: Contribution to conferencePaperpeer-review

    6 Citations (Scopus)

    Abstract

    In the thiosulfate gold leaching process, thiosulfate is used to complex gold following electrocatalytic oxidation of the native metal by Cu(II)-ammines. Unfortunately, Cu(II) complexes also catalyse the undesirable conversion of thiosulfate to polythionates. We have been seeking alternatives to ammonia, which fulfil the role of ammonia but minimize thiosulfate decomposition. One aspect of these studies has involved the determination of the rate of thiosulfate oxidation by the Cu(II) complexes from UV-Visible spectral changes. Various ligand classes, including pyridyls, polyamines, aminocarboxylates and picolinates, have been tested and the majority found to inhibit thiosulfate decomposition. Interesting variations in reactivity with the nature and denticity of the ligand and L/M ratio have been observed. In the case of open chain polyamine ligands with 2 to 5 nitrogen donors, the rate of thiosulfate oxidation was generally found to decrease with the denticity and the concentration of each ligand. Saturation of the Cu(II) coordination sphere appears to inhibit the oxidation of thiosulfate when excess thiosulfate is present. The Cu(II) complex of the branched polyamine ligand, tris(2-aminoethyl)amine (tren) exhibits this behaviour in excess thiosulfate. Interestingly, when the [Cu(tren)(OH2)]2+ complex is in excess oxidation of thiosulfate was observed. This unexpected finding prompted a spectrophotometric study of this reaction which has revealed that the oxidation of thiosulfate involves several processes, two of which involve the formation and decay of a tetrathionate radical.

    Original languageEnglish
    Pages213-226
    Number of pages14
    Publication statusPublished - 2003
    EventHydrometallurgy 2003: Proceedings of the 5th International Symposium - Vancouver, BC, Canada
    Duration: 24 Aug 200327 Aug 2003

    Conference

    ConferenceHydrometallurgy 2003: Proceedings of the 5th International Symposium
    Country/TerritoryCanada
    CityVancouver, BC
    Period24/08/0327/08/03

    Fingerprint

    Dive into the research topics of 'Alternative copper(II) catalysts for gold leaching: Use of multidentate ligands to control thiosulfate oxidation'. Together they form a unique fingerprint.

    Cite this