Studies on the Hydrolysis of Metal Ions. 46. Uranyl Ion UO22+, in Chloride, Perchlorate, Nitrate, and Sulfate Media. Survey and Introduction.

The hydrolysis of uranium(VI) in sulfate media

“…An examination of the models presented in the table indicates that the number and stoichiometry of the species proposed in the present study for the 1.0 mol dm −3 Na 2 SO 4 data is similar to that proposed by Grenthe and Lagerman [1] for 1.5 mol dm −3 Na 2 SO 4 and 0.5 mol dm −3 Na 2 SO 4 /2.0 mol dm −3 NaClO 4 , and identical to that proposed in a recent study by Moll et al [15] for 1.5 M Na 2 SO 4 . At the lower ionic strength (0.10 mol dm −3 Na 2 SO 4 ), two additional species are proposed, namely UO 2 OH + and (UO 2 ) 3 (OH) 5 + . This latter model, however, is similar to that proposed by Sylva and Davidson [7] to explain their uranyl hydrolysis data in 0.10 mol dm −3 KNO 3 .…”

“…It is possible, however, to determine the stability constants for reactions (5), as defined by equation (6), (6) provided that the activity coefficients for the reactants and products remain relatively constant throughout the fairly large changes in the composition of the test solutions [1]. Following the methodology described by Grenthe and Lagerman [1], stability constants have been determined for the ternary species, (2,2,2), (3,4,3), (4,7,4) and (5,8,4).…”

“…, the major polymeric uranium(VI) hydrolysis species in other ionic media [5][6][7][8]. Grenthe and Lagerman [1] suggested that ternary uranium(VI) hydroxo-sulfate species are formed in sulfate media, but that oxide and/or hydroxide bridges are retained in the ternary complexes.…”

A Comparison Between Unirradiated UO2(s) and Schoepite Solubilities in 1 Μ NaCl Medium

“…The polynuclear complex (U0 2 ) 4 (0H)^ is not very well established. The literature values of the equilibrium constant are not well defined by the scarce experimental data, [25][26][27]. Based on this, the ΝΕΑ review, [14], gives only an estimation for the formation constant.…”

Uranium secondary phase formation during anoxic hydrothermal leaching processes of UO2 nuclear fuel

“…The results of this procedure need to be interpreted with some care. As mentioned, it is so far not clear if U(VI) complexation will only proceed until the neutral chloro complex (as selected by the NEA [19]) or if it may include the formation of negatively charged complexes (as suggested in [25]). We calculated theoretical E H values that correspond to the measured U(VI)-U(IV) ratios; these demonstrate that for the pH-neutral solutions (pure and Ca added), actual ratios should in fact have a higher fraction of U(IV) whereas for the alkaline systems, U(VI) should in fact prevail.…”