Thermodynamic investigation reveals temperature-dependent solubility and interaction parameters in uranyl nitrate aqueous systems, highlighting improved geochemical modeling of uranium waste.
The present work improves the understanding on uranium(vi) nitrate systems in acidic, moderate to high ionic strength conditions. Undersaturation solubility studies with the systems UO₂(NO₃)₂-NaNO₃-H₂O and UO₂(NO₃)₂-Mg(NO₃)₂-H₂O were conducted at T = (22 ± 0.2) °C. Corresponding solid phases UO₂(NO₃)₂·6H₂O, NaNO₃, and Mg(NO₃)₂·6H₂O were identified via X-ray powder diffraction. Experimental results are compared with literature data available for the ternary systems at T = 25 °C and indicate a strong dependence on temperature. Based on solubility and isopiestic data, an updated Pitzer model assuming the full dissociation of all involved salts is derived, including new Pitzer interaction parameters ^θUO₂²⁺$,Na$^+$, $^θ$UO$_2²⁺,Mg²⁺, ^ΨUO₂²⁺$,Na$^+$,NO$³⁻$, and $^Ψ$UO$_2²⁺,Mg²⁺,NO³⁻. The geochemical code PhreeSCALE was used together with the PhreeSCALE database and the parameter estimation software PEST.
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Häusler et al. (2026) studied this question.
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