Dos Santos P F, Lassin A, Gaona X, Garbev K, Altmaier M, Madé B
Institute for Nuclear Waste Disposal, Karlsruhe Institute of Technology, Karlsruhe, Germany.
Water, Environment, Process Development and Analysis Division, BRGM, Orléans, France.
Dalton Trans. 2024 Apr 2;53(14):6289-6299. doi: 10.1039/d3dt04322c.
The solubility of Eu(III) was investigated under undersaturated conditions in acidic, dilute to concentrated MgSO and NaSO solutions at = (22 ± 2) °C. After attaining equilibrium conditions, solid phases were characterized by a multi-method approach, including X-ray diffraction (XRD), Raman and infrared (IR) spectroscopy, quantitative chemical analysis (ICP-OES) and thermogravimetric analysis (TG-DTA). A total of 45 solubility samples were investigated for the systems Eu(SO)-MgSO-HO (19 samples) and Eu(SO)-NaSO-HO (26 samples). Eu(SO)·8HO(cr) was found to control the solubility of Eu(III) in all investigated MgSO solutions, as well as in dilute NaSO systems. The transformation of Eu(SO)·8HO(cr) into the double salt NaEu(SO)·2HO(cr) was observed at mNaSO > 0.01 mol kg. The latter phase is characterized by significantly lower solubility. Based on these experimental solubility measurements, thermodynamic and activity models were proposed based on the Pitzer equations considering the full dissociation of the Eu(III) species in MgSO and NaSO aqueous solutions, deliberately excluding Eu(III)-sulfate complex formation. A combination of the geochemical calculation code PhreeSCALE and the parameter estimation code PEST was used to determine the values of solubility products and binary and ternary specific interaction parameters ((0)ij, (1)ij, ϕij, , ).
