Molecular dynamics simulation of aqueous ZnCl2 solutions

An important medium for ore transport within the Earth is by hydrothermal f luids. To understand ore transportation processes by hydrothermal fluids it is necessary to determine the clustering of dissolved ionic species in aqu eous solution. We have chosen sphalerite, an important zinc containing mine ral, as an example. We describe the results of Molecular Dynamics simulatio ns to predict which chlorozinc complexes will occur at the pressures and te mperatures found in the Earth's crust. Potentials have been derived for zin c-water and zinc-chloride interactions using density functional calculation s. Although the DFT calculations provide good gas-phase clusters, the resul ting potentials do not work well when modelling aqueous solutions. We there fore describe attempts to modify the potential to compensate for these effe cts. We show that at low chloride concentrations the dominant species are Z n(H2O)(6)(2+) and ZnCl(H2O)(5)(+). At higher temperatures there are a signi ficant number of clusters which contain more than one zinc with bridging ch loride ions. In aqueous solutions with a high chloride concentration the do minant species are Zn(H2O)(6)(2+), ZnCl2 (H2O)(4)(0) and ZnCl3 (H2O)(3)(-). There are almost no clusters containing more than one zinc.