Copper in Hydrothermal Systems: a Thermodynamic Description of Hydroxocomplexes

Abstract

The experimental data available in the literature on the solubility of Cu(met.) and Cu2O (cuprite) in water under hydrothermal conditions have been processed. Key experiments were carried out on the solubility of cuprite at 300 C, saturated vapor pressure of H2O, vs. pH of the solution. As a result, a set of values of thermodynamic properties for 25°C, 1 bar and parameters of the HKF (Helgeson-Kirkham-Flowers) and AD (Akinfiev-Diamond) equation of states for Cu(I) hydroxocomplexes was obtained, which make it possible to describe their behavior in a wide range of temperatures (0 – 600 C), pressures (1 – 3000 bar) and densities of aqueous fluid (0.01 – 1 gcm–3). As it has been shown by thermodynamic modeling the Cu+ ion is prevalent in the acidic and weakly alkaline regions of the aqueous solvent over the entire temperature and pressure range studied. The effect of the neutral CuOH hydroxocomplex begins to show up in the alkaline region at T 300 C and grows with increasing temperature. The second copper hydroxocomplex Cu(OH)2– shows up only in the strongly alkaline region, and the temperature has almost no effect on its behavior