首页|Silver complexation in chlorine- and sulfur-rich hydrothermal fluids: Insight from ab initio molecular dynamics simulations
Silver complexation in chlorine- and sulfur-rich hydrothermal fluids: Insight from ab initio molecular dynamics simulations
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NSTL
Elsevier
Silver (Ag) is a precious metal and has been widely used in a variety of high-technology areas, and it is mainly mined from the various of hydrothermal deposits. To quantify changes of silver solubility in hydrothermal fluids, many previous studies were focused on the thermodynamic properties of silver complexation with single ligands under different P-T conditions. Recent studies have revealed that the mixed complexes of metals (including Au, Ag and Cu) are of great significance in improving their transportation efficiency. However, the behavior of mixed silver complexes is not substantially constrained by different ore formation conditions. In this study, eight ab initio molecular dynamics (MD) simulations were designed to investigate the stoichiometries and relative stabilities of AgCl(HS)(-) and Na[AgCl(HS)] complexes in solution boxes containing various Cl- and HS- concentrations within the temperature range 25 to 900 degrees C and under pressures above the water-saturation pressures. The results revealed that the AgCl(HS)(-) and Na[AgCl(HS)] complexes remained relatively stable at temperatures between 25 and 600 degrees C and 900 degrees C, respectively. The complexes were distorted linearly, and the degree of distortion increased with increasing the solution temperature. The thermodynamic properties of the AgCl(HS)(-) and Na[AgCl(HS)] complexes were obtained using ab initio thermodynamic integration under T-P conditions corresponding to those of MD simulations. The logK values for the formation of the AgCl(HS)(-) complex at 25-600 degrees C were obtained for the first time. Ag+ + Cl- + HS- = AgCl(HS)(-) The logK values for this reaction at 25 degrees C, 200 degrees C, 350 degrees C, and 600 degrees C were 13.12, 10.52, 10.46 and 10.13, respectively. The logK value for the formation of the Na[AgCl(HS)](-) complex at 900 degrees C was obtained to compare it with that of a the previous study. Ag+ + Cl- + HS- + Nat = Na[AgCl(HS)] The standard Gibbs energy for formation of Na[AgCl(HS)] complex in our study is highly consistent with that in a the previous report from Yin and Zajacz (2018). In addition, the newly obtained thermodynamic properties for the AgCl(HS) - complex were then used to build equilibrium models, which suggested that the stability of the AgCl(HS)(-) complex increases progressively with increasing temperature. Water-rock interaction modeling with and without the addition of this mixed-ligand complex indicated that the AgCl(HS)(-) complex plays at most a minor role in the transport of silver at temperatures below 200 degrees C but could be a predominant complex of silver in geofluids at elevated temperatures.
Ab initio molecular dynamicsAb initio thermodynamic integrationSilver complexMixed-ligand complexDEGREES-CTHERMODYNAMIC PROPERTIESSULFIDE COMPLEXESPREDICTIVE MODELSYSTEM H2O-NACLTEMPERATURESCOPPERSOLUBILITY1000-DEGREES-C0-DEGREES-C
NSTL
Elsevier
