Solubility of chlorargyrite (AgCl) in water vapor at elevated temperaturesand pressures

The solubility of chlorargyrite (AgCl) in undersaturated water vapor was in vestigated at temperatures of 300 to 360 degrees C and pressures up to 180 bars. It was shown that the presence of water Vapor increases the concentra tion of AgCl in the gas (vapor) phase by between 1.5 and 2 orders of magnit ude. This phenomenon is attributed to the formation of hydrated gaseous par ticles. Silver chloride dissolved in water vapor without changing its stoic hiometry (congruent dissolution, Ag:Cl = 1:1). On the basis of the experime ntal data obtained in this study, the process of chlorargyrite dissolution, and the formation of hydrated gaseous particles in water vapor can be desc ribed by the reaction: AgClcryst + 3 . H2Ogas = AgCl .(H2O)(3)(gas) Considering that Ag is coordinated by three molecules of water and one mole cule of chlorine in the AgCl .(H2O)(3)(gas) particle, it was assumed that t he silver atom is in fourfold coordination. The properties of the AgCl .(H2 O)(3) particle were refined using ab initio molecular orbital calculations, and the stable geometry of the particle was deduced to have C3 symmetry. The temperature dependence of the equilibrium constant for the reaction con trolling the formation of AgCl .(H2O)(3)(gas) is described by the equation: logK((P=1bar)) = (22.578 +/- 5.505) - (0.0255 +/- 0.0045).TK - (11987.6 +/- 658.5)/TK Preliminary calculations suggest that water vapor can transport significant quantities of silver, and that such transport may play an important role i n mobilizing silver in natural hydrothermal systems. Copyright (C) 1999 Els evier Science Ltd.