Sphalerite solubilities in NaHS-NaCl-H₂S aqueous solutions from 100° to 240°C

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Solubilities of sphalerite were measured in NaHS-NaCI-H₂S aqueous solutions at temperatures between 100° and 240°C. The sphalerite solubilities at the experimental condition were also calculated using the thermodynamic data for Zn-sulfide and Zn-chloride complexes. The measured solubilities are systematically higher than the calculated ones by 0.5 m to 1.5 m in log unit. These discrepancies could be reconciled if a mixed sulfide-chloride complex, Zn(HS)₂Cl^-, is assumed to be present in the solutions. The equilibrium constant (log K) for a reaction ZnS(s)+H₂S(aq)+Cl^-=Zn(HS)₂Cl^- is calculated as -3.81±0.49 at 100°C, -3.60±0.62 at 150°C, -3.55±0.66 at 200°C and -4.03±0.51 at 240°C. This result suggests that the concentration of Zn(HS)₂Cl^-is higher than that of Zn-sulfide complexes at geologically important ranges of ΣS and ΣCl. Besides the Zn-chloride complexes, Zn(HS)₂Cl^- is likely to be a significant zinc species in natural ore-forming solutions.