16089-60-4Relevant articles and documents
Catalytic reduction of U(VI) with formic acid in acid solutions on palladium catalysts
Boltoeva,Shilov,Anan'ev
, p. 46 - 51 (2008)
The kinetics of catalytic reduction of U(VI) with formic acid in H 2SO4 solutions in the presence of Pd/SiO2 catalysts differing in the size of nanocrystallites of the active metal was studied. A decrease in the size of supported Pd particles leads to a decrease in the specific activity of the catalyst, i.e., the catalytic centers located on large crystallites exhibit higher activity. An increase in the Pd percent content on SiO2 leads to a decrease in the activity of the catalytic centers, which is caused by a considerable increase in the contribution of the side reaction of catalytic decomposition of HCOOH with an increase in the number of active centers in the catalyst grain. The results obtained are interpreted on the basis of the concepts of the energy nonuniformity of the surface atoms and of the reaction mechanism. The results show that the size of Pd nanocrystallites is an important factor of the selectivity of palladium catalysts in the preparation of U(IV) by catalytic reduction with formic acid.
A structural and thermodynamic study of the complexes of U(vi) with azinecarboxylates
Lv, Lina,Chen, Baihua,Liu, Jun,Chen, Jing,Xu, Chao,Yang, Yanqiu
, p. 566 - 577 (2019)
Complexation of U(vi) with pyridazine-3-carboxylate (PDZ) and pyrazine-2-carboxylate (PAZ) was studied by spectrophotometry, potentiometry and microcalorimetry in 1.0 mol dm?3 NaClO4. Three complexes, [UO2L]+, UO2L2(aq) and [UO2L3]?, were identified and their stability constants (log?β) and the corresponding formation enthalpies were determined. The thermodynamic parameters indicate that the formation of the three complexes is endothermic and driven exclusively by entropy. 1H and 13C-NMR data provide insight into the coordination modes of the complexes which corroborate with the thermodynamic data. Ligands chelate to U(vi) via κ2(N,O) coordination mode in complexes [UO2L]+ and UO2L2(aq). The crystal structures of four U(vi) complexes, [(UO2)(PAZ)2(H2O)]·H2O(i), [(UO2)(PDZ)2(H2O)](ii), [(UO2)(PDZ)3Na2ClO4]·2H2O(iii), and [(UO2)2(PDZ)4(H2O)2]·2H2O(iv), were determined by single-crystal X-ray diffraction and compared with the U(vi) complex with picolinate (PA) (CH6N3)[UO2(PA)3] in the literature. The structure data suggest that the carboxylates coordinate with uranium in O═C-O-U mode. The strengths of the U-O-C-C-N chelate cycles in the U(vi)/L complexes decrease with the trend of PA > PDZ > PAZ, which is in great agreement with the trend of thermodynamic parameters in aqueous solutions. It is interesting that in compound II two PDZ molecules coordinate with U(vi) in cis-planar positions via κ2(N,O) mode, but in other metal complexes of the three ligands having the same κ2(N,O) coordination mode the two ligand molecules are all in trans-arrangement. In the dimeric complex IV, one ligand coordinate with U(vi) in κ2(N,O) mode, while the other does it in μ2-L-κ2(O:O′) mode respectively.
Enhanced Dissolution of PuO2 in Nitric Acid using Uranium(IV)
Inoue, Akihiko
, p. 1195 - 1198 (1988)
The dissolution of PuO2 is a fundamental problem in nuclear technology.In this work the effect of the U4+ ion on the rate of dissolution of PuO2(s) inHNO3 was tested by experimental measurements.The U4+ ion greatly increases the rate of dissolution crystalline of PuO2 powder in 5 mol dm-3 HNO3 at 90 deg C.
CHEMISTRY OF URANIUM IN GLASS-FORMING MELTS: REDOX INTERACTIONS OF URANIUM WITH CHROMIUM AND IRON IN ALUMINOSILICATES.
Schreiber,Balazs,Kozak
, p. 340 - 346 (1983)
The objectives of this study were to determine the degree and the nature of the mutual interactions of uranium with chromium and with iron by internal redox reactions within aluminosilicate melts.
Reduction of U(VI) and some fission products in HNO3 media by galvanostatic electrolysis
Nogami,Hirose,Arai,Wei,Kumagai
, p. 358 - 360 (2008)
In order to investigate the applicability of the galvanostatic reduction of uranium(VI) to U(IV) in the electrolytic reduction and ion exchange (ERIX) Process, a novel aqueous reprocessing technique for spent mixed uranium and plutonium oxide (MOX) fuels for fast-breeder reactors (FBR), an improved electrolytic cell was developed and fundamental electrolytic properties were examined using U and some fission products (FPs) in HNO3 media. As the result of the electrolysis for a 200 cm3 solution of 0.5 M (M = mol/dm3) U(VI), 6 M HNO3, and 0.5 M N2H4, it was found that more than 99% of U(VI) was reduced to U(IV) before the shift to the side reaction when the initial constant current supplied was no higher than 10 A. It was also found that the reduction of U(VI) to U(IV) was achieved using the cell under coexistence with the FPs, e.g. noble metals, which are easily deposited by the electrolytic reduction.
Kern, E. F.
, p. 685 - 726 (1901)
Selbin, J.,Ortego, J. D.
, p. 657 - 671 (1969)
Oxidation of U(VI) with oxygen in weakly acidic and neutral solutions
Shilov,Yusov,Fedoseev,Peretrukhin,Gogolev,Delegard
, p. 470 - 475 (2007)
The kinetics of U(IV) oxidation with atmospheric oxygen in solutions with pH 2-7 was studied. In the kinetic curves there is an induction period, which becomes shorter with increasing pH. The induction period is caused by accumulation of U(VI), whose initial presence in the working solution accelerates oxidation. The pseudo-first-order rate constants and bimolecular rate constants of U(IV) oxidation with oxygen were evaluated. The mechanism of U(IV) oxidation is considered. At pH higher than 3, formation of a polymer of hydrolyzed U(IV) with U(VI) plays an important role in oxidation of U(IV), since this prevents formation of U(V). Heating accelerates oxidation of U(IV) at pH 2-2.5, but at a higher pH the process becomes difficultly controllable.
