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)
Abstract
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 Pitzermore »
- Authors:
-
- Karlsruhe Inst. of Technology (KIT) (Germany). Inst. for Nuclear Waste Disposal; Los Alamos National Lab. (LANL), Carlsbad, NM (United States)
- 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 Volume: 131; 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. https://doi.org/10.1016/j.jct.2018.10.019
Yalçıntaş, Ezgi, Çevirim-Papaioannou, Neşe, Gaona, Xavier, Fellhauer, David, Neck, Volker, and Altmaier, Marcus. 2018.
"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. https://doi.org/10.1016/j.jct.2018.10.019. https://www.osti.gov/servlets/purl/1482016.
@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},
url = {https://www.osti.gov/biblio/1482016},
journal = {Journal of Chemical Thermodynamics},
issn = {0021-9614},
number = ,
volume = 131,
place = {United States},
year = {Wed Oct 24 00:00:00 EDT 2018},
month = {Wed Oct 24 00:00:00 EDT 2018}
}
Web of Science
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