Molecular Dynamics simulation of aqueous ZnC12 solutions

An important medium for ore transport within the Earth is by hydrothermal fluids. To understand ore transportation processes by hydrothermal fluids it is necessary to determine the clustering of dissolved ionic species in aqueous solution. We have chosen sphalerite, an important zinc containing mineral, as an example. We describe the results of Molecular Dynamics simulations to predict which chlorozinc complexes will occur at the pressures and temperatures found in the Earth's crust. Potentials have been derived for zinc-water and zinc-chloride interactions using density functional calculations. Although the DFT calculations provide good gas-phase clusters, the resulting potentials do not work well when modelling aqueous solutions. We therefore describe attempts to modify the potential to compensate for these effects. We show that at low chloride concentrations the dominant species are Zn(H₂O)²⁺ ₆, and ZnC1(H₂O)⁺ ₅. At higher temperatures there are a significant number of clusters which contain more than one zinc with bridging chloride ions. In aqueous solutions with a high chloride concentration the dominant species are Zn(H₂O)²⁺ ₆, ZnC1₂(H₂O)⁰ ₄ and ZnC1₃(H₂O)^? ₃. There are almost no clusters containing more than one zinc.