Behaviour of U(VI) solids under conditions of natural aquatic systems

Abstract Solid-liquid equilibria of U(VI) under 100, 0.98 and 0.03% CO 2 partial pressures were studied in the pH range 2.8–4.6 in 0.1 M NaClO 4 solution at 24±2 °C. UO 2 CO 3 and UO 3 ·2H 2 O are found as solubility limiting solid phases with 1g K sp (UO 2 CO 3 )=−13.89±0.11 and 1g K sp (UO 3 ·2H 2 O)=−22.28±0.19. Furthermore, free energies of formation were calculated to be ΔG° f (UO 2 CO 3 )=−1562.2±3.3 kJ mol −1 and ΔG° f (UO 3 ·2H 2 O)=−1633.3±3.5 kJ mol −1 .