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Title: Challenging the thorium-immobility paradigm

Journal Article · · Scientific Reports
ORCiD logo [1]; ORCiD logo [2];  [3]; ORCiD logo [2];  [3]; ORCiD logo [2]
  1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States); McGill Univ., Montreal, QC (Canada)
  2. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  3. McGill Univ., Montreal, QC (Canada)
+ Show Author Affiliations

Thorium is the most abundant actinide in the Earth’s crust and has universally been considered one of the most immobile elements in natural aqueous systems. This view, however, is based almost exclusively on solubility data obtained at low temperature and their theoretical extrapolation to elevated temperature. The occurrence of hydrothermal deposits with high concentrations of Th challenges the Th immobility paradigm and strongly suggests that Th may be mobilized by some aqueous fluids. Here, we demonstrate experimentally that Th, indeed, is highly mobile at temperatures between 175 and 250°C in sulfate-bearing aqueous fluids due to the formation of the highly stable Th(SO4)2 aqueous complex. The results of this study indicate that current models grossly underestimate the mobility of Th in hydrothermal fluids, and thus the behavior of Th in ore-forming systems and the nuclear fuel cycle needs to be re-evaluated.

Research Organization:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Organization:
USDOE Laboratory Directed Research and Development (LDRD) Program; USDOE National Nuclear Security Administration (NNSA)
Grant/Contract Number:
89233218CNA000001
OSTI ID:
1597339
Report Number(s):
LA-UR--19-20286
Journal Information:
Scientific Reports, Journal Name: Scientific Reports Journal Issue: 1 Vol. 9; ISSN 2045-2322
Publisher:
Nature Publishing GroupCopyright Statement
Country of Publication:
United States
Language:
English

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Properties of lithium under hydrothermal conditions revealed by in situ Raman spectroscopic characterization of Li2O-SO3-H2O (D2O) systems at temperatures up to 420 °C journal February 2017
In situ observations of liquid–liquid phase separation in aqueous MgSO4 solutions: Geological and geochemical implications journal February 2013
Sulfate brines in fluid inclusions of hydrothermal veins: Compositional determinations in the system H2O-Na-Ca-Cl-SO4 journal July 2017
An experimental study of the solubility and speciation of thorium in chloride-bearing aqueous solutions at temperatures up to 250 °C journal October 2018
Fractionation of REE, U, and Th in natural ore-forming hydrothermal systems: Thermodynamic modeling journal January 2019
Mineral chemistry of Rare Earth Element (REE) mineralization, Browns Ranges, Western Australia journal July 2013
Visual and in situ Raman spectroscopic observations of the liquid–liquid immiscibility in aqueous uranyl sulfate solutions at temperatures up to 420°C journal June 2016
Energetics of a Uranothorite (Th 1– x U x SiO 4 ) Solid Solution journal September 2016
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Hydrolysis of thorium( iv ) at variable temperatures journal January 2016
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Solubility and hydrolysis of tetravalent actinides journal January 2001
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Studies on Metal Carbonate Equilibria. 23. Complex Formation in the Th(IV)--H2O--CO2(g) System. journal January 1991
Solubility and hydrolysis of tetravalent actinides text January 1999

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