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Thermodynamic description of U(IV) solubility and hydrolysis in chloride systems: Pitzer activity model for the system U$^{4+}$–Na$^+$–Mg$^{2+}$–Ca$^{2+}$–H$^+$–Cl$^-$–OH$^-$–H$_2$O(l)

Yan, Y. 1; Çevirim-Papaioannou, N. ORCID iD icon 1; Gaona, X. ORCID iD icon 1; Fellhauer, D. 1; Altmaier, M. ORCID iD icon 1
1 Institut für Nukleare Entsorgung (INE), Karlsruher Institut für Technologie (KIT)

Abstract:

This study presents updated chemical, thermodynamic, and activity models for the system U$^{4+}$–Na$^+$–Mg$^{2+}$–Ca$^{2+}$–H$^+$–Cl$^-$–OH$^-$–H$_2$O(l)derived using the Pitzer formalism and a strict ion interaction approach. The models build on comprehensive solubility datasets in dilute to concentrated NaCl, MgCl$_2$, and CaCl$_2$ solutions. The Nuclear Energy Agency-Thermochemical Database (NEA-TDB) selection of solubility and hydrolysis constants in the reference state were taken as anchoring point, and were extended further with the solid nanocrystalline phase UO$_2$∙H$_2$O(ncr) and the ternary complex Ca$_4$[U(OH)$_8$]$^{4+}$. The former was identified in long-term solubility experiments at ambient conditions, whereas the latter has been selected in analogy to Th(IV), Np(IV), and Pu(IV) considering experimental evidences available for these An(IV) in alkaline, concentrated CaCl$_2$ solutions. These models represent an improved tool for the calculation of U(IV) solubility and aqueous speciation in a variety of geochemical conditions including concentrated brine systems relevant in salt-based repositories for nuclear waste disposal.


Verlagsausgabe §
DOI: 10.5445/IR/1000173698
Veröffentlicht am 28.08.2024
Cover der Publikation
Zugehörige Institution(en) am KIT Institut für Nukleare Entsorgung (INE)
Publikationstyp Zeitschriftenaufsatz
Publikationsmonat/-jahr 09.2024
Sprache Englisch
Identifikator ISSN: 0883-2927, 1872-9134
KITopen-ID: 1000173698
HGF-Programm 32.11.01 (POF IV, LK 01) Nuclear Waste Disposal
Erschienen in Applied Geochemistry
Verlag Elsevier
Band 171
Seiten 106091
Vorab online veröffentlicht am 06.07.2024
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