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.
Catalytic reduction of U(VI) with hydrazine on palladium catalysts in acid solutions
Boltoeva,Trefilova,Anan'ev
, p. 38 - 45 (2008)
The stability of finely dispersed palladium supported on silica gel with respect to various acids was studied. It was shown that palladium catalysts can be used in moderately acidic media under reducing conditions. In nitric acid solutions within a wide range of experimental conditions, the palladium catalysts do not initiate reduction of U(VI) with hydrazine. The catalytic properties of palladium catalysts differing in the size of nanocrystallites of the active metal were examined in the reduction of U(VI) with hydrazine in sulfuric acid solutions. The specific activity of Pd/SiO2 catalysts is determined solely by the size of metal nanocrystals and is independent of the metal content on the support. The negative size effect is observed, i.e., the surface Pd atoms located on large crystallites exhibit higher catalytic activity. The results obtained were interpreted on the basis of the concepts of the energy nonuniformity of the surface atoms and of the mechanism of U(VI) catalytic reduction with hydrazine in the sulfuric acid solutions.
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.
Radiolytic yield of UIV oxidation into UV1: A new mechanism for Uv reactivity in acidic solution
Atinault,De Waele,Belloni,Le Naour,Fattahi,Mostafavi
, p. 2080 - 2085 (2010)
The yields of the radiolytic oxidation of UIV and of the U VI formation, measured by spectrophotometry, are found to be the same (G(-UIV)N2o - G(UVI)N20 = 8.4 x 10 -7 mol J-1) and almost double the H2 formation yield (G(H2) = 4.4 x 10-7 mol J-1) in the 60Co y radiolysis of N2O-aqueous solutions in the presence of 2 mol L-1 Cl- at pH - 0 (HCl). According to the mechanism of UIV radiolytic oxidation, we show that under the conditions of our experiments the Uv ions do not disproportionate, but undergo a stoichiometric oxidation into UVI by H- with forming H2.
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.
Three Mechanisms in One Material: Uranium Capture by a Polyoxometalate–Organic Framework through Combined Complexation, Chemical Reduction, and Photocatalytic Reduction
Zhang, Hailong,Liu, Wei,Li, Ao,Zhang, Duo,Li, Xiaoyan,Zhai, Fuwan,Chen, Lanhua,Chen, Long,Wang, Yanlong,Wang, Shuao
, p. 16110 - 16114 (2019)
The design and synthesis of uranium sorbent materials with high uptake efficiency, capacity and selectivity, as well as excellent hydrolytic stability and radiation resistance remains a challenge. Herein, a polyoxometalate (POM)–organic framework material (SCU-19) with a rare inclined polycatenation structure was designed, synthesized through a solvothermal method, and tested for uranium separation. Under dark conditions, SCU-19 can efficiently capture uranium through ligand complexation using its exposed oxo atoms and partial chemical reduction from UVI to UIV by the low-valent Mo atoms in the POM. An additional UVI photocatalytic reduction mechanism can occur under visible light irradiation, leading to a higher uranium removal without saturation and faster sorption kinetics. SCU-19 is the only uranium sorbent material with three distinct sorption mechanisms, as further demonstrated by X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge structure (XANES) analysis.
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.
Electronic spectral studies of some uranium(V) compounds
Selbin,Ortego,Gritzner
, p. 976 - 982 (1968)
The following solid compounds were prepared and characterized in inert atmospheres: MUCl6 (M = Rb and (n-C3H7)4N), both new compounds in regard to the cation present; UCl5·SOCl2; UCl5·PCl5; and UCl5·TCAC (TCAC = trichloroacrylyl chloride, Cl2C=CClCOCl), a new compound. In addition, solutions of UCl5 in CCl4 and SiCl4 were prepared. Infrared spectra were obtained. Electronic spectra in the near-ir and visible region were obtained for the MUCl6 compounds dissolved in SOCl2; for UCl5·TCAC dissolved in SOCl2, C6H6, CS2, and CCl4; for UCl5·SOCl2 dissolved in SOCl2 and CCl4; and for UCl5 in CCl4 and SiCl4. Electronic as well as vibronic band assignments have been made for these 5f1 electronic systems and several of the vibrational frequencies of the UCl6- species have been deduced from the electronic spectra. The first esr spectra for pure U(V) compounds, obtained with powdered samples, are reported, and the average g values are all 1.1.
Influence of conditions on the potential of the couple of nonoxygenated U5+/U4+ ions bound in complexes with the P 2W17O6110- and SiW 11O398- anions
Shilov,Yusov,Fedoseev,Moisy
, p. 455 - 459 (2008)
The formal potential of the couple of nonoxygenated U5+/U 4+ ions bound in complexes with unsaturated heteropoly anions (HPAs) P2W17O6110- (I) and SiW 11O398- (II) in 0-1 M NaNO3 and 1 M (NaCl + HCl) in the range of pH 0.7-4.7 was measured. In 1 M NaNO3 solutions at pH 4.7-3.0 for I and 4.3-3.9 for II, the formal potentials are constant: 0.820 and 0.730 V, respectively. They preserve approximately the same value with a decrease in pH to 0.7 in 1 M (NaCl + HCl). The potential noticeably decreases with a decrease in the NaNO3 or NaCl concentration from 1 M to 0 (pH 4.1-4.7): to 0.09 and 0.05-0.06 V for I and II, respectively. Approximate constancy of the potential of the U5+/U4+ couple with a decrease in pH to 1 and lower distinguishes this couple from the M4+/M3+ couples (M = Ce, Am, Bk) whose potential appreciably grows with increasing acidity. This is due to the fact that the U5+ and M4+ ions in acid solutions remain in the form of complexes with the ratio M: HPA = 1: 2, whereas the M3+ ions pass into the form of 1: 1 complexes. Thus, variation of the formal potentials of all the M n + 1/Mn+ couples in the presence of H+ and Na+ ions is associated with variation of the stability constants of the complexes M(HPA)2, which, in turn, is caused by interaction of single-charged ions with HPA. However, the H+ and Na+ ions interact with HPA by different mechanisms and therefore affect the potential of the U5+/U4+ couple differently.
