| Popis |
There is an intensive research effort directed to finding suitable oxide ceramics for use as radioactive waste storage forms [1,2] and to finding new innovative methods of their preparation. A good example of these methods is rapidly developing application of sonochemistry. In this work we used non-radioactive nuclides as models for highly radioactive elements. For example, based on the charge analogy and similarities in ionic radii, we used La3+ for Am3+, Ce4+ for Pu4+ and UO22+ for PuO22+. We studied sonochemically driven synthesis of insoluble lanthanide and uranium containing precipitates from the selected metal precursors, such as metal acetylacetonates, in organic solvent – tetraglyme (tetraethylenglycol dimethylether, TGL). Sonolysis of a series of metal acetylacetonato complexes, M(acac)3, M = La, Ce, Pr, Nd, Eu, Gd, Dy, Er, and UO2(acac)2 was carried out in TGL under Ar atmosphere on a Sonics and Materials VXC system with 500 W input power and working frequency of 20 kHz. The precursors (0.50 g) were dissolved in 50 cm3 of a solvent, purged with Ar gas and cooled with a Julabo F 25-MP thermostat. Sonication was run for 8 hours under Ar atmosphere. The products were separated from the mother liquors by centrifugation on a Heraeus Labofuge 400 at 3000-3500 rpm. The precipitates were washed by isopropanol and hexane and left to dry in open air. After separation they can be easily transformed to the respective metal oxides by calcination. The products were characterized by ICP-OES elemental analysis for their metal content, by nitrogen adsorption/desorption isotherm for surface area. Thermal behavior of obtained samples was studied by TG/DSC analysis. Amorphous character of precipitates and resulting phase content after calcination at 1000 C during TG/DSC analysis were studied by PXRD analysis. The sonolysis of M(acac)n, n = 2, 3, in TGL provided amorphous powders with major bands in their IR spectra corresponding to a vas(COO) and vs(COO) vibration of acetates produced by the acac ligand decomposition. Some samples featured high surface areas up to 380 m2 g-1 measured by the BET analysis. Calcination of the powders to 1000 C during TG/DSC analysis in air and mixed atmosphere (90 % N2, 10 % air) led to the formation of U3O8, CeO2, Pr6O11, and other corresponding Ln2O3 oxides. Also efficiencies of metals precipitation from the mother liquor have been calculated using data from the ICP-OES and TG/DSC with PXRD, and obtained results were compared. In this case efficiency of metals precipitation up to the 95 % was observed.
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