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Title: Fractionation of REE, U, and Th in natural ore-forming hydrothermal systems: Thermodynamic modeling

Abstract

This contribution presents a thermodynamic model revealing the mechanisms responsible for separation of Heavy and Light Rare Earth (HREE and LREE) phosphates in natural hydrothermal systems at temperatures of 250–350 °C. Our calculations were performed for an isothermal column of rock containing 0.5 wt% of apatite (Ca phosphate), which served as an immobilizing agent for REE dissolved in the solution. REE were transported by 10 wt% NaCl acidic solution. The model accounted for formation of REE phosphate solid solutions through a regular mixing model. It demonstrates that hydrothermal flushing can efficiently separate REE forming xenotime (HREE phosphate solid solutions) at the beginning of the column, and re-transportation of monazite (LREE rich) to the end of the column. This separation is primarily due to the fact that at elevated temperatures stability LREE chloride complexes is significantly higher than that for HREE. The model also evaluates behavior of U and Th, which accompany REE in vast majority of natural locations. It was found that U strongly fractionates to xenotime, whereas Th fractionates to monazite. Finally, this phenomenon can be explained by the differences in crystal-chemical characteristics between monazite and xenotime, and the mobility of Th in aqueous solutions at elevated temperatures.

Authors:
ORCiD logo [1];  [2]; ORCiD logo [1]; ORCiD logo [1];  [3]
  1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  2. Washington State Univ., Pullman, WA (United States). Dept. of Chemistry and Alexandra Navrotsky Inst. for Experimental Thermodynamics
  3. McGill Univ., Montreal, QC (Canada). Dept of Earth and Planetary Sciences
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
USDOE Laboratory Directed Research and Development (LDRD) Program
OSTI Identifier:
1479963
Report Number(s):
LA-UR-18-27417
Journal ID: ISSN 0021-9614
Grant/Contract Number:  
AC52-06NA25396
Resource Type:
Accepted Manuscript
Journal Name:
Journal of Chemical Thermodynamics
Additional Journal Information:
Journal Volume: 128; Journal Issue: C; Journal ID: ISSN 0021-9614
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Earth Sciences; REE hydrothermal monazite xenotime

Citation Formats

Migdissov, Artaches, Guo, Xiaofeng, Nisbet, Haylea Dawn, Xu, Hongwu, and Williams-Jones, Anthony E. Fractionation of REE, U, and Th in natural ore-forming hydrothermal systems: Thermodynamic modeling. United States: N. p., 2018. Web. doi:10.1016/j.jct.2018.08.032.
Migdissov, Artaches, Guo, Xiaofeng, Nisbet, Haylea Dawn, Xu, Hongwu, & Williams-Jones, Anthony E. Fractionation of REE, U, and Th in natural ore-forming hydrothermal systems: Thermodynamic modeling. United States. doi:10.1016/j.jct.2018.08.032.
Migdissov, Artaches, Guo, Xiaofeng, Nisbet, Haylea Dawn, Xu, Hongwu, and Williams-Jones, Anthony E. Wed . "Fractionation of REE, U, and Th in natural ore-forming hydrothermal systems: Thermodynamic modeling". United States. doi:10.1016/j.jct.2018.08.032. https://www.osti.gov/servlets/purl/1479963.
@article{osti_1479963,
title = {Fractionation of REE, U, and Th in natural ore-forming hydrothermal systems: Thermodynamic modeling},
author = {Migdissov, Artaches and Guo, Xiaofeng and Nisbet, Haylea Dawn and Xu, Hongwu and Williams-Jones, Anthony E},
abstractNote = {This contribution presents a thermodynamic model revealing the mechanisms responsible for separation of Heavy and Light Rare Earth (HREE and LREE) phosphates in natural hydrothermal systems at temperatures of 250–350 °C. Our calculations were performed for an isothermal column of rock containing 0.5 wt% of apatite (Ca phosphate), which served as an immobilizing agent for REE dissolved in the solution. REE were transported by 10 wt% NaCl acidic solution. The model accounted for formation of REE phosphate solid solutions through a regular mixing model. It demonstrates that hydrothermal flushing can efficiently separate REE forming xenotime (HREE phosphate solid solutions) at the beginning of the column, and re-transportation of monazite (LREE rich) to the end of the column. This separation is primarily due to the fact that at elevated temperatures stability LREE chloride complexes is significantly higher than that for HREE. The model also evaluates behavior of U and Th, which accompany REE in vast majority of natural locations. It was found that U strongly fractionates to xenotime, whereas Th fractionates to monazite. Finally, this phenomenon can be explained by the differences in crystal-chemical characteristics between monazite and xenotime, and the mobility of Th in aqueous solutions at elevated temperatures.},
doi = {10.1016/j.jct.2018.08.032},
journal = {Journal of Chemical Thermodynamics},
number = C,
volume = 128,
place = {United States},
year = {2018},
month = {8}
}

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