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81.
Ehsan Zolfonoun Seyed Reza Yousefi 《International journal of environmental analytical chemistry》2016,96(3):203-211
In this work, multi-walled carbon nanotubes (MWCNTs)-coated cellulose acetate membrane was used for on-line extraction and pre-concentration of uranium from aqueous samples prior to inductively coupled plasma optical emission spectrometry (ICP-OES) determination. Sample solutions containing the U(VI)-2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (Br-PADAP) complex were passed through the membrane. The adsorbed analyte was subsequently eluted from the membrane with acid, which was directly introduced into the ICP-OES nebuliser. The main variables affecting the pre-concentration and determination steps of uranium were studied and optimised. Under the optimised conditions, the enrichment factor of 150 and the detection limit of 0.16 μg L–1 were obtained. This method was successfully used for determination of uranium in environmental water samples. 相似文献
82.
N,N-Dialkylamides (monoamides) are known as extractants for U and Pu, and many studies have been carried out mainly by single-stage batch method. We have focused on two monoamides: N,N-di(2-ethylhexyl)-2,2-dimethylpropanamide (DEHDMPA) and N,N-di(2-ethylhexyl)butanamide (DEHBA), and proposed a multistage extraction process for recovering U and Pu by these monoamides. A continuous counter-current experiment was carried out to demonstrate the validity of this process. This process consisted of two cycles, and the 1st cycle and the 2nd cycle employed DEHDMPA and DEHBA as extractants, respectively. The feed solution for the 1st cycle was 5.1 mol/dm3 (M) nitric acid containing 0.92 M U, 1.6 mM Pu, and 0.6 mM Np. The raffinate collected in the 1st cycle was used as the feed for the 2nd cycle. The ratios of U recovered in the U fraction and U-Pu fraction were 99.1% and 0.8%, respectively, and the ratios of U in the used solvents were <0.04%. The ratio of Pu recovered in the U-Pu fraction was 99.7%, and the ratio of Pu in the used solvents was in the order of 10–3–10–4%. The concentration ratio of U with respect to Pu in the U-Pu fraction was 9, and this indicated that Pu was not isolated. The decontamination factor of U with respect to Pu in the U fraction was obtained as 4.5×105. These results supported the validity of the proposed process. 相似文献
83.
Uranium extraction using DEHCNPB (butyl-1-[N,N-bis(2-ethylhexyl)carbamoyl]nonyl phosphonic acid, a bifunctional cationic extractant) has been studied to better understand mechanism differences depending on the original acidic solution (phosphoric or sulfuric). Solvent extraction batch experiments were carried out and the organic phases were probed using 31P-NMR. This technique enabled to demonstrate that phosphoric acid is poorly extracted by DEHCNPB ([H3PO4]org < 2mM), using direct quantification in the organic phase by 31P-NMR spectra integration. Moreover, in the presence of uranium in the initial phosphoric acid solution, uranyl extraction by DEHCNPB competes with H3PO4 extraction.Average stoichiometries of U(VI)-DEHCNPB complexes in organic phases were also determined using slope analysis on uranium distribution data. Uranium seems to be extracted from a phosphoric medium by two extractant molecules, whereas more than three DEHCNPB on average would be necessary to extract uranium from a sulfuric medium. Thus, uranium is extracted according to different mechanisms depending on the nature of the initial solution. 相似文献
84.
We have studied the microscopic properties of the tetragonal UCu5Al Kondo compound by 27Al and 63,65Cu NMR in the paramagnetic state. NMR and susceptibility measurements performed on the powdered sample, but oriented along the applied field, showed χ>χ. Plots of K(T) against χ(T) at temperatures T≥100 K yield the transferred hyperfine fields of +5.9 kOe/μB for 27Al nuclei, and +5.3 and −7.0 kOe/μB for 65Cu nuclei in crystallographically inequivalent Cu(2) and Cu(1) sites, respectively. The Knight shift vs. susceptibility plots for T<100 K exhibit a deviation from the linear behaviour (absolute values of shifts become smaller than expected). We attribute this finding to the crystalline electric field effect in similar way as it was reported for several Ce-based compounds. The random distribution of the Al and Cu(2) atoms in the crystal lattice we consider as a reason of an unusual broadening of the NMR spectra, particularly at low temperatures. 相似文献
85.
Synthesis and Crystal Structure of U2Ta6O19, a New Compound with “Jahnberg‐Structure” and a Note to the First Oxide Chlorides in the Systems Th/Nb/O/Cl and Th/Zr(Hf)/Nb/O/Cl Black crystals of U2Ta6O19 with hexagonal shape were obtained (at T1) by chemical transport using HCl (p (HCl, 298 K) = 1 atm; silica tube) as transport agent in a temperature gradient (T2 → T1; 1000 °C → 950 °C) and using a mixture of UO2, Ta2O5, and HfO2 (or ZrO2) (1 : 2 : 2) as starting materials (at T2). For the structure determination the best result was achieved in space group P63/mcm (No. 193, a = 6.26(2) Å, c = 19.86(6) Å). U2Ta6O19 is isotypical to Th2Ta6O19. In the crystal structure each uranium atom is surrounded by oxygen atoms like a bi‐capped trigonal antiprism and tantalum atoms like a pentagonal bipyramid (CN = 7). Like the “Jahnberg Structures” both coordination polyhedra arrange themselves in separate layers (U–O‐polyhedra, in o‐, Ta–O‐polyhedra in p‐layers) so that in the direction of the c‐axis the sequence of layers is p‐p‐o. Using chemical transport it was possible to prepare the compounds Th12Nb16O63Cl2 and Th8M4Nb16O63Cl2 (M = Zr, Hf), which are the first quaternary and quinquinary examples in these systems. They crystallize isotypically. 相似文献
86.
采用TBP-萃淋树脂吸附三氧化铀样品中的铀,硫酸根与铬酸钡进行交换反应后,直接比色法测定硫酸根的含量。实验中研究了三氧化铀样品中硫酸根含量测定的样品制备、分离、反应酸度,煮沸时间,铬酸钡用量等影响因素。优化条件下,采用硝酸(5mol/L)淋洗、1mL HCl溶液(2.5mol/L)调节溶液中酸浓度、使用2mL BaCrO_4进行交换反应、煮沸3min,得到方法相对标准偏差小于10%,加标回收率为92.9%~110%。实验结果表明,直接显色的测定方法灵敏、快速、准确度高。方法测定条件易于获得,适于推广应用。 相似文献
87.
研究了三辛基氧化膦(TOPO)和三丁基氧化膦(TBPO)在离子液体(ILs) 1-烷基-3-甲基咪唑双三氟甲基磺酰亚胺盐(CnmimNTf2, n=2, 4, 6, 8)中萃取分离UO2(NO3)2. TOPO-C2mimNTf2和TOPO-C4mimNTf2体系萃取UO2(NO3)2时会出现三相, 而TBPO萃取UO2(NO3)2的萃合物可以很好地溶解在所有离子液体中. 论文也考察了萃取过程中的萃取剂浓度效应、酸效应、盐效应. 水相加入HNO3会降低萃取效率. 盐效应证明了萃取是一种阳离子交换机理. 水相中加入NO3-能够提高U的萃取, 这说明NO3-参与萃取. 选择性研究表明: 除了在高酸度下对Zr 的显著萃取, TBPO-C4mimNTf2萃取体系在低酸度下对U呈现较好的选择性; 去除U后, 在低酸度下该体系对三价Nd 仍保持较好的选择性. 通过定量比较离子液体中NO3-进入量, 电喷雾质谱(ESI-MS)和紫外光谱表征确定了TBPO-CnmimNTf2中萃取机理的差异性. 萃取中存在两种萃合物, 即UO2(TBPO)3(NO3)+和UO2(TBPO)32+, 其中UO2(TBPO)3(NO3)+的比例从C2mimNTf2体系到C8mimNTf2体系逐渐增加. 相似文献
88.
P.R. Alonso J.R. Fernndez P.H. Gargano G.H. Rubiolo 《Physica B: Condensed Matter》2009,404(18):2851-2853
The U–Al binary system exhibits the formation of three intermetallic compounds: cubic Laves phase C15 UAl2, cubic L12 UAl3, and orthorhombic D1b UAl4. However, some uncertainties are found in the literature concerning UAl4 structure and composition. A computational first principles based approach is a useful tool to shed some light on this problem. To the author's knowledge there are no such contributions. UAl4 stabilization with composition and uranium constitutional vacancies is specially discussed. 相似文献
89.
90.
The 2,6-pyridinedicarboxylic acid (PDA) has been shown to efficiently sensitize and enhance the fluorescence of uranium in aqueous medium. Interestingly, this ligand stabilizes the UO22+ species, which without the ligand is known to be in a negligible concentration, in aqueous medium at pH 6. The ligand sensitized enhancement of UO22+ fluorescence by PDA, provides an analytical tool for the determination of uranium at trace levels, in aqueous medium. Furthermore, PDA is also known to enhance the fluorescence of lanthanides; consequently, the simultaneous determination of uranium and lanthanides, using PDA as a fluorescence sensitizing agent, becomes a possibility, which has been demonstrated in this work. We have shown that the use of PDA yields detection limits of 2.2×10−7 M for UO22+, 1×10−8 M for Tb3+ and 5×10−9 M for Eu3+ in the simultaneous determination of these analytes. 相似文献