M A T T E R A T E X T R E M E S

S C I E N T I F I C H I G H L I G H T S

1 6 H I G H L I G H T S 2 0 2 1 I

Fig. 3: a) Platinum L3-edge XANES spectra of experimental S-bearing aqueous solutions recorded at 275°C and 700 bars using the BM30 autoclave and compared with quantum-chemistry simulated XANES spectra of representative [Pt-HS-S3]-type complexes

with structures optimised using molecular modelling. b) A 3D snapshot of dissolved platinum in hydrothermal fluid obtained from molecular dynamics simulations. Coupled with in-situ spectroscopy, such simulations provide information about the atomic structure and stability of chemical species in aqueous fluids that deliver critical metals to ore deposits in the Earth s crust. Water molecules are

depicted as red-and-white boomerangs; sulfur, platinum and sodium ions are shown, respectively, as yellow, brown and pink spheres.

Unexpectedly, it was found that this minor sulfur ligand binds very strongly to both Pt(II) and Pt(IV) ions, thereby enabling their transport at tenors 10 000 times more than any other Cl- or S-bearing ligand allows. The molecular structure and thermodynamic stability of the Pt-[S3

]− complexes derived in this work enables far-improved predictions of the factors controlling Pt solubility, transport and precipitation by aqueous fluids, both in natural and technological contexts. Quite remarkably, the chemical affinity of the [S3

]− ion for platinum (which is equivalent to the thermodynamic stability of a complex) is many orders of magnitude greater than for gold and other more common metals [4].

This discovery may have new applications in geosciences, economic geology and nanotechnology. Acting like powerful vehicles, the trisulfur radical ions are capable of carrying tens to hundreds of grams of Pt per cubic metre of fluid, fulfilling one of the fundamental conditions of metal ore deposit formation the presence of a metal- enriched fluid phase. Therefore, the study may offer ways to identify new potential resources of this eagerly sought metal. Furthermore, the strong selectivity of [S3

]− for Pt and, potentially, for electronically similar metals of the PGE family (e.g., Pd, Ir) could be used to improve selective extraction of those metals from ore as well as to explore new routes for PGE-based nanomaterials synthesis.

PRINCIPAL PUBLICATION AND AUTHORS

The trisulfur radical ion S3 − controls platinum transport by hydrothermal fluids, G.S. Pokrovski (a), M.A. Kokh (a), E. Desmaele (b), C. Laskar (a), E.F. Bazarkina (c,d), A.Y. Borisova (a,e), D. Testemale (c), J.-L. Hazemann (c), R. Vuilleumier (b), G. Ferlat (f), A.M. Saitta (f), Proc. Natl. Acad. Sci. U.S.A. 118(34), e2109768118 (2021); https:/doi.org/10.1073/pnas.2109768118 (a) Experimental Geosciences Team (GeoExp), Géosciences Environnement Toulouse (GET), CNRS, University of Toulouse (France) (b) PASTEUR, Département de Chimie, École Normale Supérieure, Paris (France) (c) Institut Néel and ESRF, Grenoble (France) (d) Institute of Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry (IGEM), Moscow (Russia) (e) Geological Department, Lomonosov Moscow State University (Russia) (f) IMPMC, Sorbonne Université, Paris (France)

REFERENCES

[1] D. Testemale et al., Rev. Sci. Instrum. 76, 043905-043909 (2005). [2] G.S. Pokrovski & L.S. Dubrovinsky, Science 331, 1052-1054 (2011). [3] G.S. Pokrovski & J. Dubessy, Earth Planet. Sci. Lett. 411, 298-309 (2015). [4] G.S. Pokrovski et al., Proc. Natl. Acad. Sci. U.S.A. 112, 13484-13489 (2015).