Abstract
Experiments were carried out using rapid-quench hydrothermal techniques to determine the solubility of bunsenite (NiO) in supercritical H 2O-NaCl-NiCl 2 solutions in the range 550 to 750°C, at 2 kbar. The solubility of NiO was enhanced by the formation of complexes of higher stoichiometry than NiCl 2 0 in the presence of increasing concentrations of aqueous NaCl. The results are consistent with the formation of the NiCl 3 − complex in the fluid over the entire temperature range, as a result of the reaction NiCl 2 0( aq) + Cl −( aq) = NiCl 3 −( aq). The variation in values of the equilibrium constant for the above reaction is given by logK eq = 3.40(±0.83) − 2365 (±758)/ T(° K). Despite the increase in solubility that results in the NaCl-bearing system, nickel should still remain a relatively immobile element, as compared to Ca, Mg, Fe and Mn, in supercritical aqueous Cl-bearing fluids, provided the activity of nickel in the coexisting solid mineral assemblage is not unusually high.
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