Yttrium speciation in sulfate-rich hydrothermal ore-forming fluids

Guan, Qiushi1,2, Mei,Dr Yuan1, Etschmann, Dr Barbara2, Louvel, Dr Marion3, Brugger, Professor Joel2

1CSIRO Mineral Resources, Kensington, WA 6151, Australia,, 2School of Earth, Atmosphere and Environment, Monash University, Clayton, VIC 3800, Australia,, 3Institute for Mineralogy, WWU Muenster, D-48149 Germany

Rare earth elements (REE) have in high demand due to their nearly unsubstituted applications but limited production, and their use as geochemical tracers. REE form strong complex with sulfate and these complexes in hydrothermal fluids are responsible for REE transport and deposition in a wide variety of geological environments, ranging from sedimentary basins to magmatic hydrothermal settings. However, the thermodynamic properties of most REE-sulfate complexes are derived from extrapolation of ambient temperature data. The direct information on REE-sulfate complexing under hydrothermal conditions is limited to a single study that derived formation constants for Nd, Sm and Er in sulfate solutions to 250 ˚C (Migdisov and William-Jones, 2008).

In this study, we employ ab initio molecular dynamics (MD) simulations to calculate the speciation and thermodynamic properties of yttrium(III) in sulfate solutions at temperatures and pressures up to 500 ºC and 800 bar. The calculated formation constants of Y-SO42- complexes are employed to fit the modified Ryzhenko–Bryzgalin (MRB) model, which enables the extrapolation of the formation constants to a wider temperature and pressure. The MD results were complemented by the in situ X-ray absorption spectroscopy (XAS) measurements. Our results show that yttrium(III) forms complexes with sulfate with both monodentate and bidentate structures over the investigated temperature range (200 ˚C to 500 ˚C). The thermodynamic properties for yttrium(III) sulfate complexes derived from MD enable a better modelling of REE transport in hydrothermal systems.


I’m a PhD student from School of Earth, Atmosphere and Environment, Monash University, and co-supervised at CSIRO. My work is to understand how the rare earth metals acts with different ions and ligands in geological environments by modelling the molecule behaviours with high performance computers

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