Transport of post-transition metals in hydrothermal fluids: thermodynamics from first-principles

Since the Bronze age, the metals Sn and Pb have been of crucial economic importance. In recent years, the neighbouring elements on the periodic table, Ga and, In have come into demand because of their use in electronic devices. Together, Sn, Pb, Ga and In are referred to as the post-transition metals. These elements have unusual electronic structures and their geochemical behaviour is different from metals such as Cu and Zn. To meet future demand, we will need to locate and assess new resources of these metals. Most ore deposits of metals are usually formed by hydrothermal fluids deep in the Earth's crust. Such fluids are able to extract trace metals from large volumes of rock and concentrate them into solutions. As the hot solutions cool, depressurise or react with minerals, they will subsequently precipitate dissolved metals as sulphide or oxide minerals and form ore deposits. However, the chemical processes by which this happens is usually a mystery. Experimental investigations of the chemistry of hydrothermal fluids at high temperatures and pressures are very difficult. However, we can gain a great deal of insight on what happens in hydrothermal fluids using computational simulations based on quantum mechanics. We can now determine how metals are complexed by dissolved ligands such as Cl-, HS- and derive equilibrium constants for these reactions entirely from first-principles. This opens the door to vast new insights on the chemistry and role of fluids in the Earth's crust. The work proposed here will apply these methods to the post-transition metal complexes with ligands such as Cl-, HS- and F to develop a thermodynamic model of mineral solubilities that can be used to understand how ore-deposits of these metals form.

The obvious industrial beneficiary of this research will be the mining industry. Understanding the nature of ore-forming hydrothermal fluids is fundamental to predicting how and where ore-deposits might form. With reliable thermodynamic models on hydrothermal fluids, we would be able to perform reactive-transport simulations of ore deposit formation. Such simulations could provide important insights for prospecting and for the assessment of known deposits. Thermodynamic models of aqueous solutions and hydrothermal fluids is also necessary for the development of hydrometallurgical extraction technologies for ore-processing. At present, the large gaps in current thermodynamic models makes reactive-transport simulations impossible. The research proposed here will fill this gap for the metals Sn, Pb, Ga and In. Metals such as Ga and In are crucial for new technologies and the future will see increasing demand for new resources.