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Issue 8, 2011
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Copper(i) speciation in mixed thiosulfate-chloride and ammonia-chloride solutions: XAS and UV-Visible spectroscopic studies

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Abstract

Thiosulfate and ammonia mixtures may be more environmentally benign alternatives to cyanide for leaching Au from ores. In this method, the Cu(I)/Cu(II) couple acts as a redox mediator aiding in the oxidative dissolution of metallic Au. Information about the speciation of Cu(I) and Cu(II) in these lixiviant solutions is paramount to the optimization of gold ore processing conditions. With this in mind, we have carried out XANES, EXAFS and UV-Vis spectroscopic studies of the speciation of Cu(I) in mixed thiosulfate-chloride and ammonia-chloride solutions. In thiosulfate-chloride solutions, the EXAFS studies indicate that the geometry of the predominant Cu(I) complex is distorted trigonal (triangular planar), with an average of 2 sulfur atoms + 1 oxygen atom occupying the coordination sphere. This indicates that the stability of the [Cu(S2O3)3]5 complex is lower than previously proposed. Formation constants for Cu(I) thiosulfate complexes have been derived on the basis of systematic UV-Vis measurements of solutions with varying [S2O3]/[Cl] ratios. Only one mixed chloride-thiosulfate complex, [Cu(H2O)(S2O3)Cl]2, was found to predominate over the range of conditions investigated. For Cu(I) in ammonia-chloride solutions, our results confirm the broad stability of [Cu(NH3)2]+ and we have also identified a stable mixed amminechlorocopper(I) complex, [CuCl(NH3)]+. XAS reveals that these two complexes share a linear geometry. This study demonstrates that combinations of methods are required to decipher the geometry and thermodynamic properties of transition metal complexes in mixed ligand chemical systems where many species may coexist. Our results allow more comprehensive predictions of solution speciation and contribute to efforts to design improved methods to process gold ore with thiosulfate and ammonia lixiviants.

Graphical abstract: Copper(i) speciation in mixed thiosulfate-chloride and ammonia-chloride solutions: XAS and UV-Visible spectroscopic studies

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Publication details

The article was received on 09 Sep 2011, accepted on 21 Sep 2011 and first published on 19 Oct 2011


Article type: Paper
DOI: 10.1039/C1RA00708D
RSC Adv., 2011,1, 1554-1566

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    Copper(I) speciation in mixed thiosulfate-chloride and ammonia-chloride solutions: XAS and UV-Visible spectroscopic studies

    B. E. Etschmann, J. R. Black, P. V. Grundler, S. Borg, D. Brewe, D. C. McPhail, L. Spiccia and J. Brugger, RSC Adv., 2011, 1, 1554
    DOI: 10.1039/C1RA00708D

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