Sonochemical precipitation of amorphous uranium phosphates from trialkyl phosphate solutions and their thermal conversion to UP2O7

Abstract

Insoluble amorphous precipitates containing uranyl and phosphate ions are obtained by sonication of solutions of three uranyl precursors, UO2(X)2, X=NO3, CH3COO, CH3C(O)CHC(O)CH3 (acetylacetonate, acac), in triesters of phosphoric acid, OP(OR)3, R=Me (trimethyl phosphate, TMP), Et (triethyl phosphate, TEP). TMP and TEP are used as high-boiling solvents and they serve also as a source of phosphate anions. Sonolysis experiments were carried out under flow of Ar at 40°C on a Sonics and Materials VXC 500W system (f=20 kHz, Pac=0.49 W cm(-3)). Powder X-ray diffraction (PXRD) reveals amorphous character of all obtained precipitates. The presence of uranyl and phosphate is evidenced by IR spectroscopy and ICP-OES analysis reveals the content of both U (38.6-43.4 wt%) and P (11.0-13.6 wt%). The thermal behavior of the substances was studied by TG/DSC analysis, which shows weight losses in the range of 19.21-24.08%. On heating the amorphous precipitates to 1000°C, crystalline uranium diphosphate UP2O7 is obtained in all cases as the only crystalline phase. Uranyl(VI) is reduced during thermolysis to U(IV) as there is no characteristic vibration of UO2(2+) in the IR spectra of solid UP2O7 products. The ICP-OES analysis of U and P content in precipitates allowed us to calculate the efficiency of precipitation of uranium from mother liquor and to compare it with the efficiency calculated from the data received by the PXRD and TG/DSC analyses. The efficiency of the uranium removal attained by our sonoprecipitation procedure was typically 30-35%. These sonochemical precipitation reactions providing insoluble uranium phosphates may be potentially interesting models for the description of behavior of uranium-containing waste or reprocessing streams.

Sonochemical catalysis as a unique strategy for the fabrication of nano-/micro-structured inorganics

“… 103 Pinkas and coworkers utilized a sonochemical precipitation method to form insoluble amorphous uranium phosphates from UO 2 2+ precursors in trialkyl phosphate solutions. 104 In this sonolysis experiment, the high-boiling trialkyl phosphates served as a phosphate source to create some active species by the decomposition of ester molecules and then reacted with uranium precursors in the solution, followed by the obtained amorphous precipitates changing into crystalline uranium diphosphate (UP 2 O 7 ) when heated to 1000 °C. The efficiency of uranium removal was higher than 30% by sonochemical precipitation, which might become a potential remote separation technology for uranium in waste streams.…”

A power-triggered preparation strategy of nano-structured inorganics: sonosynthesis

“…Pinkas et al obtained insoluble amorphous uranium phosphates from UO 2 2+ precursors in high-boiling trialkyl phosphate solutions by sonication. 96 Sonolysis experiments were carried out in a frequency of 20 kHz and a power of 0.49 W cm −3 under an argon flow at 40 °C, in which trialkyl phosphates served as a phosphate source creating phosphate species by the decomposition of ester molecules and then reacted with uranium precursors. The efficiency of uranium removal from the solution by sonochemical precipitation was higher than 30%, and the obtained amorphous uranium precipitates could change into crystalline uranium diphosphate (UP 2 O 7 ) when heated to 1000 °C.…”

Interaction Mechanism of U(VI) with Redox Active Covalent Organic Framework: EXAFS Spectroscopy and XPS analysis

“…To date, several techniques have been used for the separation and extraction of uranium from different aqueous streams. These include mainly solvent extraction [9][10][11][12], exchange resins [13][14][15][16], membrane-based extraction [17][18], reductive precipitation [19][20] and electrochemical extraction [21][22].…”