Transformation of schoepite into uranyl oxide hydrates of the bivalent cations Mg2+, Mn2+ and Ni2+

Abstract

The magnesium, manganese and nickel uranyl oxide hydrates have been synthesized by the reaction of the appropriate metal salts with schoepite at elevated temperature. After separation from the reaction mixture, the chemical composition of the different compounds was determined, and the chemical formulae were calculated based on different structural hypotheses. X-Ray powder diffraction data were obtained from each of the three species. After indexing and unit-cell parameter determination, the most plausible space groups were proposed, and compared with the known space groups of existing uranyl oxide hydrates.Thermal analysis was performed to determine the character and the number of water molecules in the structures. The solubility and solubility products were determined, and the influence of the different uranyl species was evaluated. Finally, to examine the presence of a charged double layer, the zeta potential was determined.

Formation of Stable Uranium(VI) Colloidal Nanoparticles in Conditions Relevant to Radioactive Waste Disposal

“…The pH at the point of zero charge for several uranyl oxyhydroxides is 4−4.5. 42 It is thus clear that U(VI) (oxyhydr)oxide nanoparticles would have a highly negative surface charge at pH 13.1. Thus, electrostatic repulsion would minimize (further) particle aggregation consistent with our observations and potentially reduce the interaction of U(VI) with materials present in a cementitious GDF system.…”

“…The persistence of a significant fraction of unaggregated primary particles (Table ) could have been caused by the high pH. The pH at the point of zero charge for several uranyl oxy-hydroxides is 4–4.5 . It is thus clear that U­(VI) (oxyhydr)­oxide nanoparticles would have a highly negative surface charge at pH 13.1.…”

Solid-Aqueous Phase Equilibria of Uranium(VI) under Ambient Conditions

“…Additional constraints are known to be temperature [30] and (in saline solutions) sodium concentrations [7,8,24,25,40], The instability of U0 3 · 2 H 2 0(s) in presence of other metal ions, e.g. Mg 2+ , Ca 2+ , Ba 2+ , Ni 2+ has been described [41,42], too. A study of U0 3 • 2 H 2 0(s) solubilities at higher ionic strength therefore will most probably be severely limited by the tendency of U0 3 · 2 H 2 0(s) to form uranates with the cation of supporting electrolytes.…”

Synthetic uranium oxide hydrate materials: Current advances and future perspectives

“…In principle, all uranium compounds can be used as uranium precursors. As such, various uranyl salts, such as nitrate and acetate, as well as uranium oxides (UO 2 and U 3 O 8 ) [14][15][16][17] and schoepite 18 were chosen in the attempted syntheses of UOH phases with a variety of alkali, alkaline earth, ammonium, 3d transition metal and lead (as the end stable element of uranium decay chain) ions. However, all reported UOH-Ln phases were synthesized using either UO 3 or schoepite as the uranium precursor to better control the solution pH.…”