Copper(i) speciation in mixed thiosulfate-chloride and ammonia-chloride solutions: XAS and UV-Visible spectroscopic studiesElectronic Supplementary Information (ESI) available: composition of solutions for XAS and UV-Visible measurements (Tables S1-S4); results of principle component analysis and residual maps for the thiosulfate-chloride and ammonia-chloride data UV-Visible data (Figures S1-S4). See DOI: 10.1039/c1ra00708d
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...
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| Main Authors | , , , , , , , |
|---|---|
| Format | Journal Article |
| Language | English |
| Published |
14.11.2011
|
| Online Access | Get full text |
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| Summary: | 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(S
2
O
3
)
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 [S
2
O
3
]/[Cl] ratios. Only one mixed chloride-thiosulfate complex, [Cu(H
2
O)(S
2
O
3
)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(NH
3
)
2
]
+
and we have also identified a stable mixed amminechlorocopper(
i
) complex, [CuCl(NH
3
)]
+
. 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.
The identity and thermodynamic properties of copper(
i
) complexes present in mixed thiosulfate- and ammonia-chloride systems have been determined using UV-Vis and XAS methods, allowing comprehensive modelling of gold-ore processing. |
|---|---|
| Bibliography: | 10.1039/c1ra00708d Electronic Supplementary Information (ESI) available: composition of solutions for XAS and UV-Visible measurements (Tables S1-S4); results of principle component analysis and residual maps for the thiosulfate-chloride and ammonia-chloride data UV-Visible data (Figures S1-S4). See DOI |
| ISSN: | 2046-2069 |
| DOI: | 10.1039/c1ra00708d |