Uranyl-chloride speciation and uranium transport in hydrothermal brines: Comment on Migdisov et al. (2018) "A spectroscopic study of uranyl speciation in chloride-bearing solutions at temperatures up to 250 °C", Geochim. Cosmochim. Acta 222, 130-145
Abstract
Migdisov et al. (2018) recently reported new thermodynamic stability constants for uranyl(VI)-chloride species containing up to 2 chlorine atoms in their equatorial plane. These data were derived from in situ UV-visible spectroscopy measurements performed under acidic conditions (pH25°C = 1.5-1.8 imposed by triflic acid), at temperatures up to 250 °C and NaCl concentrations up to 1.5 M (mol l-1). Based on these thermodynamic data a new uranyl speciation model in NaCl-bearing solutions is proposed at temperatures up to 300 °C and NaCl concentrations up to 10 m (mol kg-1). These data are further used to model UO2/U3O8 solubility in hydrothermal NaCl-bearing solutions and to explain the high uranium concentration reported in fluid inclusions from unconformity-related uranium (URU) deposits having chlorinity up to 9 m (Derome et al., 2005; Richard et al., 2011). While agreeing that uranyl-chloride complexes play a key role in transporting uranium under URU deposits condition, we make the following notes about (1) the validity of Migdisov et al.'s speciation model at chlorinity above 1 m, and (2) the misuse of the thermodynamic data reported by Dargent et al. (2013).
- Publication:
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Geochimica et Cosmochimica Acta
- Pub Date:
- August 2018
- DOI:
- 10.1016/j.gca.2018.05.015
- Bibcode:
- 2018GeCoA.235..505D