A critical review of the solution chemistry, solubility, and thermodynamics of europium: Recent advances on the Eu(III) hydrolysis

This review is aiming at providing a critical assessment of the published complexation constants and solubility products related to the hydrolysis of Eu(III) in aqueous medium. Original experimental data available from peer-reviewed scientific publications were the main source for the selection of thermodynamic data, together with technical reports and Eu(III)-data-containing thermodynamic databases starting from around 1940 until July 2023. The methodology followed by the reviewers of the Thermochemical Database Project of the Nuclear Energy Agency, which uses the Specific ion Interaction Theory (SIT) for describing activity coefficients in aqueous electrolyte solutions, was strictly applied, with a few minor deviations, however. The selected and rejected literature data were thoroughly discussed as well as the procedures enabling the derivation of recommended complexation constants, solubility products, thermodynamic functions at infinite dilution (1 bar, 25 °C), together with ion interaction coefficients ε(j;k). These recommended data complement our former study on the chloride, sulphate, and phosphate ligands and will further contribute to the establishment of a comprehensive, internally consistent, and reliable thermodynamic reference database for the chemical, geochemical, and chemotechnical modeling of europium.