Publication details

Sonochemical Synthesis of Uranium Phosphates



Year of publication 2014
Type Conference abstract
MU Faculty or unit

Central European Institute of Technology

Description One of the most critical problems of current times is centered at the storage of nuclear wastes. There is a pressing need for increasing chemical and mechanical stability and durability of the waste forms[1] and at the same time also for decreasing complexity and expenses of the preparation and storage. Embedding waste radioactive ions in the mineral-like ceramic matrices is one of the best methods for immobilization and subsequent geological storage.[2] Nowadays there are many types of ceramics studied and used for storage, especially monazite and xenotime-like phosphate ceramics. A contribution to developing of alternative preparation methods potentially allowing remote precipitation and synthesis of insoluble waste forms is described below. In this work we studied sonochemically driven synthesis of uranium phosphates from the selected precursors, such as uranyl nitrate, acetate and acetylacetonate, in organic solvents. Trialkylphosphates, OP(OR)3, R = Me (TMP), Et (TEP), n-Bu (TBP) were used in the role of solvents and also as a source of phosphate groups. After sonolysis, insoluble precipitates were obtained. After separation they can be easily transformed to the respective phosphates by calcination. The products were characterized by ICP-OES elemental analysis for uranium and phosphorus content, by nitrogen adsorption/desorption isotherms for surface area. Thermal behavior of obtained samples was studied by TG/DSC analysis. Amorphous character of the precipitates and resulting phase content after calcination at 1000 oC during TG/DSC analysis were identified by PXRD analysis. Sonolyses of precursors were carried out in reactive solvents TMP, TEP, and TBP (with addition of water) 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. Yellow-green precipitates were separated from the mother liquors by centrifugation on a Heraeus Labofuge 400 at 3000-3500 rpm and after washing by isopropanol and hexane left to dry in open air. Absorption bands corresponding to v(PO) bonds in the IR spectra confirmed their phosphate nature. Calcination of obtained samples at 1000 oC under mixed (90 % N2, 10 % air) atmosphere led to the formation of UP2O7 in the case of TMP and TEP and some mixture of uranium phosphates phases in the case of TBP. Also efficiencies of uranium precipitation from the mother liquor have been calculated using data from the ICP-OES and TG/DSC with PXRD, and obtained results were compared. Efficiencies of precipitation of uranium were around 30 %.
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