The solubility of Pt and Pd sulfides and Au in bisulfide solutions |
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| Authors: | S A Wood P Pan Y Zhang A Mucci |
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| Institution: | (1) Department of Geological Sciences, McGill University, H3A 2A7 Montreal, Quebec, Canada;(2) Present address: Department of Geology and Geological Engineering, University of Idaho, 83843 Moscow, ID, USA;(3) Present address: Department of Chemistry, Memorial University of Newfoundland, A1B 3X7 St. John's Newfoundland, Canada |
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| Abstract: | Two sets of measurements of the solubility of Pt and Pd in bisulfide solutions have been carried out at low temperatures. The first involved the equilibration of Pt metal with bisulfide solutions at 25 °C and pH = 6–12 for periods up to five years. These experiments yielded Pt concentrations on the order of tens of  g/L at sulfide concentrations as low as 0.001 molal under conditions too reducing to permit significant contributions from hydroxide complexes. The second set of experiments consisted of reacting PtS, PdS and Au with H2S-saturated solutions having pH values of 3–4 at 25°, 50° and 90 °C. These experiments showed that the solubilities of all three metals increased with temperature. The observed order of solubility was Au > Pt  Pd. Solubilities ranged from 10 to 75 g/L Au, 4 to 20 g/L Pt and 0.5 to 10 g/L Pd. The data do not permit definitive identification of the Pt and Pd species present in either set of experiments, but do strongly suggest that the species present under acidic and basic conditions are different. The measured solubility of gold at 25° and 50 °C is consistent with that measured in previous studies.Although the measured Pt and Pd solubilities are not as high as those estimated by theoretical methods, it is nevertheless evident that bisulfide complexation can lead to the remobilization of Pt and Pd over a wide range of pH under reducing conditions at geologically reasonable sulfide concentrations, at low as well as high temperatures. Such conditions are characteristic of a wide variety of geological environments where Pt and Pd have been inferred to have been affected by hydrothermal transport. In these cases, bisulfide complexation is far more effective than chloride or hydroxide complexes in transporting the PGE.
On leave from: Shenyang Laboratory of Rock and Mineral Resources, Ministry of Geology and Mineral Resources, People's Republic of China |
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