The solubility of cooperite PtS(cr) at 25 – 450 °C, Psat – 1000 bar and hydrosulfide complexing of platinum in hydrothermal fluids

Stability and structure of platinum sulfide complexes in hydrothermal fluids

“…This tendency would be in agreement with the decrease of both fluid density and dielectric constant favoring ion association and uncharged or weakly-charged species stability (Tödheide, 1982;Walther and Schott, 1988;Da Silva et al, 2009;Hou et al, 2020). For Pt, such a tendency was likely to be confirmed by Kokh et al (2017) and Filimonova et al (2021) who inferred, from bulk solubility measurements, Pt(HS) 2 0 to be the dominant Pt species in much more dilute H 2 S solutions (≤0.05 m) and temperatures of 450 °C. In addition, ion-pairing with alkali ions may contribute to the metal speciation at such conditions as shown by solubility studies (e.g., Zajacz, 2010Zajacz, , 2011.…”

“…No attempt was made to re-process in a similar way the data of Pan and Wood (1994) and Filimonova et al (2021) because their speciation is likely to be different from ours. Filimonova et al…”

“…The rare studies of Pt sulfide type complexes at hydrothermal conditions are both inconsistent and controversial. This is because all of them employed the bulk solubility approach to the PtS(s) and PtS 2 (s) solid phases using hydrothermal reactors (Gammons and Bloom, 1993;Pan and Wood, 1994;Kokh et al, 2017;Filimonova et al, 2021;Pokrovski et al, 2021). Such solubility experiments are intrinsically difficult to perform and interpret both because of the low, often ppb-level, Pt dissolved concentrations posing severe analytical challenges, and the narrow pH and sulfur concentration ranges that may practically be covered by such experiments.…”

“…More recently, Filimonova et al (2021) measured PtS(s) solubility in dilute H 2 S/HSsolutions (pH=3-8, 0.01-0.2 m S) at 50-75 °C, 1 bar, and at 450 °C, 1000 bar, using batch reactors quenched at the run end. They tentatively interpreted their data by Pt(HS) 2 0 as the dominant species, with PtS(s) solubility magnitudes matching those of Gammons and Bloom (1993) and Kokh et al (2017).…”

“…S2), compared to all other experiments conducted at pH <9. This discrepancy might be due to the formation of additional Pt-HS-S complexes at such alkaline pH (e.g., Filimonova et al, 2021), probably with the S 2ion that was predicted to form in significant amounts at pH >10 according to theoretical estimations of its dissociation constant by Phillips and Phillips (2000).…”