Stability and structure of platinum sulfide complexes in hydrothermal fluids - Archive ouverte HAL Accéder directement au contenu
Article Dans Une Revue Geochimica et Cosmochimica Acta Année : 2022

Stability and structure of platinum sulfide complexes in hydrothermal fluids

Résumé

Knowledge of the chemical speciation of platinum and the solubility of Pt-bearing minerals in hydrothermal fluids is required to assess Pt transport, remobilization and concentration in the Earth’s crust. In this study, we combined PtS(s) solubility measurements in a hydrothermal reactor allowing fluid sampling, in situ X-ray absorption spectroscopy, and first-principles molecular dynamics simulations to systematically investigate the structure, composition and stability of Pt sulfide complexes in model aqueous H2S-bearing solutions up to 300 °C and 600 bar. The results demonstrate that tetrahydrosulfide, PtII(HS)42–, is the major Pt-bearing complex in aqueous solutions saturated with PtS(s) over a wide range of dissolved hydrogen sulfide concentrations, from <0.2 to ~2 molal. The equilibrium constants of the dissolution reaction of PtS(s) generated in this study, PtS(s) + 3 H2S(aq) = Pt(HS)42– + 2 H+ (β4), are described by the equation log10β4= 0.9×1000/T(K)–19.7 (±0.5) over the temperature range 25–300 °C and pressure range Psat–600 bar. Furthermore, the stepwise formation constants of four PtII-HS complexes, Pt(HS)+, Pt(HS)20, Pt(HS)3–, and Pt(HS)42–, were estimated, for thefirst time, from molecular dynamics simulations. The generated constants indicate that the maximum solubility of platinum in the form of Pt(HS)42– in reduced H2S-dominated hydrothermal fluids at moderate temperatures (≤350 °C) is close to 1 ppb Pt at near-neutral pH of 6–8 and hydrogen sulfide concentrations of 0.1 molal. Although this solubility is much greater than that of Pt-Cl, Pt-OH and Pt-SO4 complexes at such conditions, it is yet too low to account for significant Pt transport in most shallow-crust hydrothermal settings, characterized by the presence of both sulfide and sulfate. Complexes with S-bearing ligands, very likely other than H2S/HS–, such as S3–, would be required to account for Pt hydrothermal mobility. Our results provide a basis for more systematic future studies, using combined approaches, of the role of hydrothermal fluids in the behavior of platinum group elements in nature.
Fichier principal
Vignette du fichier
PtHS_Laskar_Journal_preproof_GCA_aug22.pdf (1.31 Mo) Télécharger le fichier
Origine : Fichiers produits par l'(les) auteur(s)

Dates et versions

hal-03805655 , version 1 (07-10-2022)

Identifiants

Citer

C. Laskar, E.F. Bazarkina, M.A. Kokh, Jean-Louis F Hazemann, R. Vuilleumier, et al.. Stability and structure of platinum sulfide complexes in hydrothermal fluids. Geochimica et Cosmochimica Acta, 2022, 336, pp.407-422. ⟨10.1016/j.gca.2022.08.015⟩. ⟨hal-03805655⟩
39 Consultations
79 Téléchargements

Altmetric

Partager

Gmail Facebook X LinkedIn More