Stability and structure of platinum sulfide complexes in hydrothermal fluids

Knowledge of the chemical speciation platinum and solubility Pt-bearing minerals in hydrothermal fluids is required to assess Pt transport, remobilization concentration Earth’s crust. In this study, we combined PtS(s) measurements a reactor allowing fluid sampling, situ X-ray absorption spectroscopy, first-principles molecular dynamics simulations systematically investigate structure, composition stability sulfide complexes model aqueous H2S-bearing solutions up 300 °C 600 bar. The results demonstrate that tetrahydrosulfide, PtII(HS)42–, major complex saturated with over wide range dissolved hydrogen concentrations, from < 0.2 ∼ 2 molal. equilibrium constants dissolution reaction generated + 3 H2S(aq) = Pt(HS)42– H+ (β4), are described by equation log10β4 0.9 × 1000/T(K) – 19.7 (± 0.5) temperature 25–300 pressure Psat–600 Furthermore, stepwise formation four PtII-HS complexes, Pt(HS)+, Pt(HS)20, Pt(HS)3–, Pt(HS)42–, were estimated, for first time, simulations. indicate maximum form reduced H2S-dominated at moderate temperatures (≤ 350 °C) close 1 ppb near-neutral pH 6–8 concentrations 0.1 Although much greater than Pt-Cl, Pt-OH Pt-SO4 such conditions, it yet too low account significant transport most shallow-crust settings, characterized presence both sulfate. Complexes S-bearing ligands, very likely other H2S/HS–, as S3–, would be mobility. Our provide basis more systematic future studies, using approaches, role behavior group elements nature.