Solubility of U(VI) in chloride solutions. II. The stable oxides/hydroxides in alkaline KCl solutions: Thermodynamic description and relevance in cementitious systems

Çevirim-Papaioannou, Neşe; Yalçıntaş, Ezgi; Gaona, Xavier; Altmaier, Marcus; Geckeis, Horst

doi:10.1016/j.apgeochem.2018.09.017

Title: Solubility of U(VI) in chloride solutions. II. The stable oxides/hydroxides in alkaline KCl solutions: Thermodynamic description and relevance in cementitious systems

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Abstract

In this study, the solubility of U(VI) is investigated from undersaturation conditions in 0.1, 0.51, 1.03, 3.31 and 4.58 m KCl–KOH solutions at pHm = 7.5–14.6 (with pH_m = –log [H⁺] in molal units). All experiments were performed under Ar atmosphere at T = (22 ± 2)°C. XRD, quantitative chemical analysis, SEM–EDS and TG–DTA confirm that K₂U₂O₇·1.5H₂O(cr) is the solid phase controlling the solubility in all evaluated systems at pH_m ≥ 9.5. Below this pH_m and with decreasing KCl concentration, the formation of sub-stoichiometric phases with K:U < 1 is indicated by XRD and solubility data. The concentration of uranium in equilibrium with K₂U₂O₇·1.5H₂O(cr) shows a pH-independent behaviour up to pH_m ≈ 11 regardless of ionic strength, whereas an increase of the solubility with a well–defined slope of +1 (log [U] vs. pH_m) is observed at pH_m ≥11. These results are consistent with the predominance of UO₂(OH)₃^– and UO₂(OH)₄^2- species as previously reported in the literature. The combination of solubility data obtained in the present study with K₂U₂O₇·1.5H₂O(cr) and the U(VI) hydrolysis scheme reported in Altmaier et al. (2017) yields a solubility product of log *K°_s,0{0.5K₂U₂O₇·1.5H₂O(cr)} = (12.0 ± 0.2). SIT ion interaction coefficients for UO₂(OH)₃^– and UO₂(OH)₄^2- with K⁺more »« less

Authors:

Çevirim-Papaioannou, Neşe ^[1]; Yalçıntaş, Ezgi ^[2];

^[1]; Altmaier, Marcus ^[1]; Geckeis, Horst ^[1]

Karlsruhe Institute of Technology (Germany)
Karlsruhe Institute of Technology (Germany); Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

Publication Date:: Wed Sep 26 00:00:00 EDT 2018

Research Org.:: Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

Sponsoring Org.:: USDOE

OSTI Identifier:: 1477656

Report Number(s):: LA-UR-18-20116
Journal ID: ISSN 0883-2927

Grant/Contract Number:: AC52-06NA25396

Resource Type:: Accepted Manuscript

Journal Name:: Applied Geochemistry

Additional Journal Information:: Journal Volume: 98; Journal Issue: C; Journal ID: ISSN 0883-2927

Publisher:: Elsevier

Country of Publication:: United States

Language:: English

Subject:: 58 GEOSCIENCES; 12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES; 36 MATERIALS SCIENCE; Environmental Protection; uranium; U(VI); solubility; hydrolysis; KCl; thermodynamics; SIT; cement

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                    Çevirim-Papaioannou, Neşe, Yalçıntaş, Ezgi, Gaona, Xavier, Altmaier, Marcus, and Geckeis, Horst. Solubility of U(VI) in chloride solutions. II. The stable oxides/hydroxides in alkaline KCl solutions: Thermodynamic description and relevance in cementitious systems.  United States: N. p., 2018. 
Web.  doi:10.1016/j.apgeochem.2018.09.017.

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                    Çevirim-Papaioannou, Neşe, Yalçıntaş, Ezgi, Gaona, Xavier, Altmaier, Marcus, & Geckeis, Horst. Solubility of U(VI) in chloride solutions. II. The stable oxides/hydroxides in alkaline KCl solutions: Thermodynamic description and relevance in cementitious systems.  United States.  https://doi.org/10.1016/j.apgeochem.2018.09.017

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                    Çevirim-Papaioannou, Neşe, Yalçıntaş, Ezgi, Gaona, Xavier, Altmaier, Marcus, and Geckeis, Horst. Wed .  
"Solubility of U(VI) in chloride solutions. II. The stable oxides/hydroxides in alkaline KCl solutions: Thermodynamic description and relevance in cementitious systems".  United States.  https://doi.org/10.1016/j.apgeochem.2018.09.017.  https://www.osti.gov/servlets/purl/1477656.

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@article{osti_1477656,

  title        = {Solubility of U(VI) in chloride solutions. II. The stable oxides/hydroxides in alkaline KCl solutions: Thermodynamic description and relevance in cementitious systems},

  author       = {Çevirim-Papaioannou, Neşe and Yalçıntaş, Ezgi and Gaona, Xavier and Altmaier, Marcus and Geckeis, Horst},

  abstractNote = {In this study, the solubility of U(VI) is investigated from undersaturation conditions in 0.1, 0.51, 1.03, 3.31 and 4.58 m KCl–KOH solutions at pHm = 7.5–14.6 (with pHm = –log [H+] in molal units). All experiments were performed under Ar atmosphere at T = (22 ± 2)°C. XRD, quantitative chemical analysis, SEM–EDS and TG–DTA confirm that K2U2O7·1.5H2O(cr) is the solid phase controlling the solubility in all evaluated systems at pHm ≥ 9.5. Below this pHm and with decreasing KCl concentration, the formation of sub-stoichiometric phases with K:U < 1 is indicated by XRD and solubility data. The concentration of uranium in equilibrium with K2U2O7·1.5H2O(cr) shows a pH-independent behaviour up to pHm ≈ 11 regardless of ionic strength, whereas an increase of the solubility with a well–defined slope of +1 (log [U] vs. pHm) is observed at pHm ≥11. These results are consistent with the predominance of UO2(OH)3– and UO2(OH)42- species as previously reported in the literature. The combination of solubility data obtained in the present study with K2U2O7·1.5H2O(cr) and the U(VI) hydrolysis scheme reported in Altmaier et al. (2017) yields a solubility product of log *K°s,0{0.5K2U2O7·1.5H2O(cr)} = (12.0 ± 0.2). SIT ion interaction coefficients for UO2(OH)3– and UO2(OH)42- with K+ are derived based on the newly generated experimental data in dilute to concentrated KCl systems and analogy with NaCl systems. This work extends the thermodynamic database available for U(VI) and allows more accurate source term calculations in the context of nuclear waste disposal under boundary conditions where significant K concentrations may be present and redox conditions lie in the stability field of U(VI). Finally, the K2U2O7·1.5H2O(cr) solid phase can be considered to control the solubility of U(VI) in the degradation phase I of cement and cementitious materials.},

  doi          = {10.1016/j.apgeochem.2018.09.017},

  journal      = {Applied Geochemistry},

  number       = C,

  volume       = 98,

  place        = {United States},

  year         = {Wed Sep 26 00:00:00 EDT 2018},

  month        = {Wed Sep 26 00:00:00 EDT 2018}

}

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https://doi.org/10.1016/j.apgeochem.2018.09.017

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