The speciation of Platinum and Palladium in aqueous carbonates*

The elements of the Platinum Group (PGEs) are considered essential commodities for the electronic and automotive industries, due to their high melting points, corrosion resistance and catalytic properties. Unfortunately, natural geochemical and petrological processes have concentrated PGE metals in rare ore deposits. It is thus important to understand how these deposits formed to eventually help discover new ores and/or improve processes for the metals’ extraction. At the fundamental level, despite recent experimental advances, the question of how hot, aqueous fluid in the Earth crust may facilitate transport of PGEs remains open. Here we investigate the speciation trend of platinum and palladium in aqueous carbonates using first principles molecular dynamics and the Qbox code (http://qboxcode.org/).  We aim at obtaining a fundamental understanding of the ion complexes at extreme conditions, including those relevant to hydrothermal and magmatic environments and we compare our results with EXAFS measurements. Specifically, we study Pt-Pd complexes in carbonate solutions under high temperature between 600K and 1000K and high pressure in range from 0.1 GPa to 10 GPa and we compute Raman spectra to identify vibrational signatures of the ions present in solution.  In addition, we aim at using our calculations to provide input for the development of a self-consistent thermodynamic solubility model as a function of temperature and pressure.