Synthesis and characterization of neptunyl(VI) and plutonyl(VI) orthosilicates

摘要

(NpO2)(2)SiO4.2H(2)O (I) and (PuO2)(2)SiO4.2H(2)O (II) have been prepared by hydrothermal synthesis technique. Chemical composition of (I) was attributed to the compound from its isostructurality with (UO2)(2)SiO4.2H(2)O; crystal unit cell parameters of (NpO2)(2)SiO4.2H(2)O have been refined as orthorhombic, a = 8.365(5) Angstrom, b = 11.089(5) Angstrom, c = 18.640(9) Angstrom with the space group Fddd. (PuO2)(2)SiO4.2H(2)O has not been found isostructural with uranyl(VI) and neptunyl(VI) analogues. Chemical composition of (II) was determined by chemical analysis and proved by the formula volume calculated from powder X-ray data. Indexing of X-ray powder pattern of the prepared compound gave the tetragonal unit cell with a = 6.912(3), c = 18.563(3) Angstrom, possible space group I4(1)/amd. Visible-near IR and IR absorption spectra of the prepared compounds have been measured in NaCl and KBr. f-f absorption band of PuO22+ in the visible spectrum of crystal (PuO2)(2)SiO4.2H(2)O is not splitted but its maximum is essentially shifted (up to 858 nm) to the long wave region in comparison with hydrated PuO22+ ions. Visible-near IR absorption spectrum of crystal (NpO2)(2)SiO4.2H(2)O is close to that of aqueous neptunyl(VI) solution. Thermal behavior of synthesized compounds has been studied up to 800degreesC in air. [References: 17]