skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Solubility of U(VI) in chloride solutions. III. The stable oxides/hydroxides in MgCl 2 systems: Pitzer activity model for the system UO 2 2+–Na +–K +–Mg 2+–H +–OH –Cl –H 2O(l)

Abstract

Here we have developed new chemical, thermodynamic and activity models for the system UO 2 2+–Na +–K +–Mg 2+–H +–OH –Cl –H 2O(l) within the Pitzer approach. The new thermodynamic model is based on previously reported data treated within the SIT approach for NaCl and KCl systems, as well as on new experimental data determined in this work for the MgCl 2 system. The solubility of uranium(VI) was studied in 0.01–5.15 mol·kg w –1 MgCl 2 solutions at pH m = 4.1–9.7 (with pH m = –log [H +]). Experiments were performed under Ar atmosphere at T = (22 ± 2) °C. In all investigated systems, the solubility of U(VI) is controlled by metaschoepite, UO 3·2H 2O(cr). In contrast to previously investigated NaCl and KCl systems, no ternary Mg–U(VI)–OH(s) solid phases formed in alkaline MgCl 2 solutions within the timeframe of this study (≤ 200 days). A very significant increase in the solubility (up to 3 log 10-units) is observed in acidic to near-neutral pH m conditions when increasing MgCl 2 concentration from 0.01 to 5.15 mol·kg w –1, which reflects the strong ion interaction processes taking place in concentrated MgCl 2 brines. The solubility of UO 3·2H 2O(cr) inmore » the investigated NaCl, KCl and MgCl 2 solutions is well described with the solubility and hydrolysis constants recommended by Altmaier et al., (2017) and NEA–TDB, and a Pitzer activity model derived in the present work. The latter model considers experimental data reported in the present study and available in the literature for NaCl, KCl and MgCl 2 systems (solubility, potentiometric and spectroscopic data), in combination with well-stablished estimation methods and correlations with SIT coefficients. Finally, chemical, thermodynamic and Pitzer activity models provided in this work for the system UO 2 2+–Na +–K +–Mg 2+–H +–OH –Cl –H 2O(l) accurately describe all evaluated datasets, and represent an adequate tool for the calculation of U(VI) solubility and aqueous speciation in a variety of geochemical conditions including concentrated brine systems of relevance in salt-based repositories for nuclear waste disposal.« less

Authors:
 [1];  [2];  [2];  [2];  [2];  [2]
  1. Karlsruhe Inst. of Technology (KIT) (Germany). Inst. for Nuclear Waste Disposal; Los Alamos National Lab. (LANL), Carlsbad, NM (United States)
  2. Karlsruhe Inst. of Technology (KIT) (Germany). Inst. for Nuclear Waste Disposal
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
USDOE; Federal Ministry for Economic Affairs and Energy (BMWi) (Germany)
OSTI Identifier:
1482016
Report Number(s):
LA-UR-18-29496
Journal ID: ISSN 0021-9614
Grant/Contract Number:  
AC52-06NA25396
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Journal of Chemical Thermodynamics
Additional Journal Information:
Journal Name: Journal of Chemical Thermodynamics; Journal ID: ISSN 0021-9614
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Energy Sciences

Citation Formats

Yalçıntaş, Ezgi, Çevirim-Papaioannou, Neşe, Gaona, Xavier, Fellhauer, David, Neck, Volker, and Altmaier, Marcus. Solubility of U(VI) in chloride solutions. III. The stable oxides/hydroxides in MgCl2 systems: Pitzer activity model for the system UO22+–Na+–K+–Mg2+–H+–OH––Cl––H2O(l). United States: N. p., 2018. Web. doi:10.1016/j.jct.2018.10.019.
Yalçıntaş, Ezgi, Çevirim-Papaioannou, Neşe, Gaona, Xavier, Fellhauer, David, Neck, Volker, & Altmaier, Marcus. Solubility of U(VI) in chloride solutions. III. The stable oxides/hydroxides in MgCl2 systems: Pitzer activity model for the system UO22+–Na+–K+–Mg2+–H+–OH––Cl––H2O(l). United States. doi:10.1016/j.jct.2018.10.019.
Yalçıntaş, Ezgi, Çevirim-Papaioannou, Neşe, Gaona, Xavier, Fellhauer, David, Neck, Volker, and Altmaier, Marcus. Wed . "Solubility of U(VI) in chloride solutions. III. The stable oxides/hydroxides in MgCl2 systems: Pitzer activity model for the system UO22+–Na+–K+–Mg2+–H+–OH––Cl––H2O(l)". United States. doi:10.1016/j.jct.2018.10.019.
@article{osti_1482016,
title = {Solubility of U(VI) in chloride solutions. III. The stable oxides/hydroxides in MgCl2 systems: Pitzer activity model for the system UO22+–Na+–K+–Mg2+–H+–OH––Cl––H2O(l)},
author = {Yalçıntaş, Ezgi and Çevirim-Papaioannou, Neşe and Gaona, Xavier and Fellhauer, David and Neck, Volker and Altmaier, Marcus},
abstractNote = {Here we have developed new chemical, thermodynamic and activity models for the system UO22+–Na+–K+–Mg2+–H+–OH––Cl––H2O(l) within the Pitzer approach. The new thermodynamic model is based on previously reported data treated within the SIT approach for NaCl and KCl systems, as well as on new experimental data determined in this work for the MgCl2 system. The solubility of uranium(VI) was studied in 0.01–5.15 mol·kgw–1 MgCl2 solutions at pHm = 4.1–9.7 (with pHm = –log [H+]). Experiments were performed under Ar atmosphere at T = (22 ± 2) °C. In all investigated systems, the solubility of U(VI) is controlled by metaschoepite, UO3·2H2O(cr). In contrast to previously investigated NaCl and KCl systems, no ternary Mg–U(VI)–OH(s) solid phases formed in alkaline MgCl2 solutions within the timeframe of this study (≤ 200 days). A very significant increase in the solubility (up to 3 log10-units) is observed in acidic to near-neutral pHm conditions when increasing MgCl2 concentration from 0.01 to 5.15 mol·kgw–1, which reflects the strong ion interaction processes taking place in concentrated MgCl2 brines. The solubility of UO3·2H2O(cr) in the investigated NaCl, KCl and MgCl2 solutions is well described with the solubility and hydrolysis constants recommended by Altmaier et al., (2017) and NEA–TDB, and a Pitzer activity model derived in the present work. The latter model considers experimental data reported in the present study and available in the literature for NaCl, KCl and MgCl2 systems (solubility, potentiometric and spectroscopic data), in combination with well-stablished estimation methods and correlations with SIT coefficients. Finally, chemical, thermodynamic and Pitzer activity models provided in this work for the system UO22+–Na+–K+–Mg2+–H+–OH––Cl––H2O(l) accurately describe all evaluated datasets, and represent an adequate tool for the calculation of U(VI) solubility and aqueous speciation in a variety of geochemical conditions including concentrated brine systems of relevance in salt-based repositories for nuclear waste disposal.},
doi = {10.1016/j.jct.2018.10.019},
journal = {Journal of Chemical Thermodynamics},
issn = {0021-9614},
number = ,
volume = ,
place = {United States},
year = {2018},
month = {10}
}

Journal Article:
Free Publicly Available Full Text
This content will become publicly available on October 24, 2019
Publisher's Version of Record

Save / Share: