A critical review of the solution chemistry, solubility, and thermodynamics of europium: recent advances on the Eu3+ aqua ion and the Eu(III) aqueous complexes and solid phases with the sulphate, chloride, and phosphate inorganic ligands

This review provides a critical assessment of the published thermodynamic data of the Eu(III) aqua ion as well as complexation constants and solubility products of Eu(III) with the SO42−, Cl−, and PO43− inorganic ligands in aqueous solution. The main source for the selection of thermodynamic data are original experimental data published in peer-reviewed papers from around 1900 until the end of 2020. This review strictly follows, with a few minor deviations, the methodology recommended by the Thermochemistry Database group of the Nuclear Energy Agency, which relies on the Specific ion Interaction Theory (SIT) for describing activity coefficients in aqueous electrolyte solutions. For each inorganic ligand, a discussion is provided on the selected as well as the rejected literature data, and the procedures leading to the derivation of recommended thermodynamic data at infinite dilution, such as solubility products and complexation constants, enthalpies and entropies of reaction, molar entropies, heat capacities, as well as ion interaction coefficients ε, are described in detail. These recommended data will contribute to the establishment of a comprehensive, internally consistent, and quality-assured thermodynamic reference database for the chemical, geochemical and chemotechnical modeling of europium and increase the robustness of applications of chemical analogies for trivalent actinides or linear free energy relationships within the lanthanide group.