SYNTHESIS AND CHARACTERIZATION OF URANYL ORTHOSILICATE (UO2)(2)SIO4-CENTER-DOT-2H(2)O

A new method was developed for the synthesis of uranyl orthosilicate, (UO2)(2)SiO4 . 2H(2)O. The method was derived from a procedure describ ed by legros et al. [1]. This compound was synthesized by reacting sto ichiometric amounts of 0.1 M solutions of uranyl acetate and sodium me tasilicate at pH = 5 and at 383 K for about 10 days in a Parr bomb. Ur anyl orthosilicate was obtained with reproducible yields of 81 +/- 2%. The final product was identified and characterized by X-ray powder di ffraction, IR-spectroscopy, ICP-MS, AAS, thermoanalysis (TG/DTG/DTA) a nd Si-29-MAS-NMR. The lattice constants were determined as a = 0.8306( 3) nm, b = 1.1245(6) nn and c = 1.8622(8)nm for the orthorhombic syste m. The substance can be dried up to 423 K without any loss of crystal water. The Si-29-MAS-NMR investigations showed that the crystalline (U O2)(2)SiO4 . 2H(2)O contains only monomeric silicate anions.