Speciation of yttrium in fluorine-rich brines at hydrothermal and metamorphic conditions

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Aqueous fluids play an important role in many geological processes. They are major transport media of chemical elements in hydrothermal and metamorphic environments. Despite this importance, the thermodynamic properties of such fluids at high temperatures and pressures are not well known. One important group of elements dissolved in and transported by fluids are the rare earth elements. Molecular modeling approaches based on quantum mechanics have become a powerful and predictive tool to study the structure and thermodynamic properties of complex fluids at the same time. Here, we propose to use ab initio molecular simulations to develop speciation models of yttrium in chlorine- and fluorine-bearing fluids. Ab initio molecular dynamics simulations will be complemented by metadynamics and thermodynamic integration methods to predict the stability constants of different solute species as a function of composition, temperature and pressure. This information will be used to construct majority species diagrams and to make predictions of Y-bearing mineral solubilities in Cl- and F-bearing geological fluids. The simulations will also provide new molecular-scale insight into the transport mechanisms of rare earth elements by hydrothermal or metamorphic fluids and the deposition of related minerals.