Journal of Chemical Thermodynamics, Vol.138, 151-158, 2019
Thermodynamic interpretation of uranium (IV/VI) solubility in the presence of alpha-isosaccharinic acid
The effect of alpha-isosaccharinic acid (ISA) on the solubility and redox of tetravalent and hexavalent uranium (U(IV), U(VI)) was investigated in the hydrogen ion concentration (pH(c) = -log [H+]) range of 6-13 and at total ISA concentration ([ISA](tot)) = 10(-4)-10(-1.2) mol/dm(3) (M). The dependence of U(IV) solubility on pH(c) and [ISA](tot) suggested the existence of U(OH)(4)(ISA)(2)(2) - as a dominant species within the investigated pH(c) range of 6-12. For the U(VI)-ISA system, UO2(OH)(3)(ISA)(2)(3) - was suggested as a dominant species at pH(c) 7-13. The formation constants of the U(IV)-ISA and U(VI)-ISA complexes were determined by least squares fitting of the solubility data. The solubility of U(IV) and U(VI) in the presence of ISA and its effect on the redox behavior were thermodynamically interpreted based on the obtained constants. (C) 2019 Elsevier Ltd.