铀酰离子发光双指数衰减的研究

本文系统地研究了铀酰离子发光双指数衰减时的时间分辨发光光谱,测定和研究了相应条件下铀(Ⅵ)的激光拉曼光谱.通过计算机对所得光谱进行定量的拟合分解表明,铀(Ⅵ)的发光双指数衰减是两种发光体UO_2~(2+)和它的水解产物(UO_2)_2(OH)_2~(2+)发光叠加的结果。     

CHEMSPEC模拟铀在塔木素地下水中的种态分布

本文使用CHEMSPEC软件模拟了铀在塔木素地下水中的种态分布,并讨论了p H、Eh、离子浓度以及温度对铀种态分布的影响.结果表明,铀在强酸性条件下,主要以UO_2~(2+)(aq)的形式存在;在弱酸性、中性以及弱碱性条件下,主要以UO_2(OH)_2(aq)的形式存在;在强碱性条件下,主要以UO_2(OH)_3~-的形式存在,可能会生成Ca UO_4沉淀. Eh33 m V时, U(OH)_4(aq)为优势种态;而Eh33 m V时, U(VI)更为稳定.不同阴离子的引入对铀的种态分布影响的大小顺序为HCO_3~-F~-SO_4~(2-)Cl~-. UO_2~(2+)浓度的增加促进了Ca UO_2(CO_3)_3~(2-)和Ca_2UO_2(CO_3)_3(aq)的生成.温度升高使塔木素地下水中UO_2OH~+的浓度显著提高.     

分子动力学方法模拟不同温度下铀酰在叶腊石上的吸附和扩散行为

采用分子动力学方法研究了铀酰在叶腊石表面的吸附和扩散。在碳酸根离子存在的情况下,探究了温度对铀酰吸附和扩散的影响。碳酸根离子与铀酰存在较强的作用力,不同数目的碳酸根离子与铀酰结合会形成多种铀酰种态。在不同温度的模拟中,得到了UO_2~(2+)、UO_2CO_3、UO_2(CO_3)_2~(2-)、UO_2(CO_3)_3~(4-)四种铀酰种态和铀酰聚合物。通过原子密度图,观察了粒子在溶液中的分布情况。发现UO_2~(2+)+和UO_2CO_3容易吸附在叶腊石上,而UO_2(CO_3)_2~(2-)和UO_2(CO_3)_3~(4-)主要存在于扩散层中。随着时间的推移,越来越多的碳酸根离子与铀酰配位,使得铀酰在叶腊石上的吸附逐渐减少。本文计算了不同温度下,各铀酰种态的扩散系数。在扩散层中,各种态的扩散系数随温度的变化较为一致,而在吸附层中,UO_2~(2+)和UO_2CO_3的扩散速率随温度的变化较UO_2(CO_3)_2~(2-)和UO_2(CO_3)_3~(4-)慢。但是在同一温度下,同一个吸附层或扩散层中,铀酰种态的扩散系数大小顺序始终保持不变:UO_2~(2+)UO_2CO_3UO_2(CO_3)_2~(2-)UO_2(CO_3)_3~(4-)。说明在碳酸根存在的情况下,UO_2~(2+)可能是主要的扩散形式。     

细菌Lelliottia sp.X-110对铀的吸附及减量化研究

本文以分离自铀污染土壤的细菌Lelliottia sp.X-110(X-110)冻干粉作为生物吸附剂,考察其在不同条件下对铀酰离子(UO_2~(2+))的吸附行为、机理及减量化效果。结果表明:pH 5时,X-110对UO_2~(2+)的吸附效果最为显著;当初始铀浓度为100 mg·L~(-1)时,吸附量可达170.76 mg·g~(-1);X-110对UO_2~(2+)的吸附过程分为前期的快速(前5 min内)和后期的慢速两个阶段,其行为符合准二级动力学和Langmuir吸附等温模型;FT-IR分析显示,X-110表面的羧基、氨基及磷酸基团参与了UO_2~(2+)的吸附作用;X-110具有较好的减量化效果,减重比为18.25。XRD进一步分析表明,灰分中的铀主要以U(UO_2)(PO_4)_2晶体形式存在,表明UO_2~(2+)主要与X-110上的磷酸基团结合。上述结果提示,Lelliottia sp.X-110有望作为吸附剂用于放射性废水中铀的去除与减量化处理。     

氢氧化铈吸附铀酰离子及其吸附机理的研究

以氢氧化铈[Ce(OH)_4]为吸附剂,研究其对铀酰离子(UO_2~(2+))的吸附行为,并对吸附实验进行了条件探索。动力学研究表明,Ce(OH)_4对UO_2~(2+)的吸附符合准二级动力学模型;此外,对吸附UO_2~(2+)前后的吸附剂进行了扫描电镜分析,结果显示,吸附前后的Ce(OH)_4形貌发生了较大改变;将Ce(OH)_4在100~600℃下焙烧后的产物进行吸附实验,发现焙烧后产物的吸附能力降低。研究结果表明,吸附机理主要是Ce(OH)_4表面的羟基与UO_2~(2+)发生了络合作用。     

用新显色剂1,1′-[2,2′-(4,4′-双噻唑基)-双偶氮]-2,2′-双萘酚与TritonX-100体系析相光度法测定微量铀

将新显色剂1,1′-[2,2′-(4,4′-双噻唑基)-双偶氮]-2,2′-双萘酚(简称4,4′-bi-TAN),用作为测定铀的高选择性的试剂。析相体系为UO_2~(2+)-4,4′-bi-TAN-TritonX-100,在580nm波长下测定UO_2~(2+),许多共存离子不干扰测定,用此法测定了铀矿废水中UO_2~(2+)的含量,结果令人满意。     

二氧化钍纳米球在碳酸铀酰铵溶液中对铀的吸附性能

二氧化钍(ThO_2)是一种锕系金属氧化物,作为吸附剂是其重要的应用方向之一,但其应用范围还较为有限,有待进一步拓宽。我们研究了水热法合成的多晶ThO_2纳米球在碳酸铀酰铵((NH_4)_4[UO_2(CO_3)_3])溶液中对铀的吸附性能。结果表明,在含有2 mmol/L NH_4HCO_3和20 mmol/L三羟甲基氨基甲烷-HCl的(NH_4)_4[UO_2(CO_3)_3]溶液(pH=8.45)中,ThO_2纳米球对铀的吸附符合准二级动力学吸附模型,在初始铀浓度为20 mg/L时,ThO_2纳米球对铀的吸附容量可以达到6.52 mg/g;ThO_2纳米球对铀的等温吸附符合Freundlich模型。吸附铀后的ThO_2纳米球可通过低浓度的盐酸进行高效洗脱。机理研究表明,在此实验条件下,ThO_2纳米球带负电荷,通过阳离子吸附机理吸附UO_2~(2+),容易受到Ca~(2+)、Cu~(2+)和Ni~(2+)等阳离子的竞争而出现吸附容量下降的情况。本文的研究工作对金属氧化物从弱碱性及中性放射性废液和海水中提取铀具有参考价值。     

配位体 SO_4~(2-)对激发态铀(Ⅵ)去活化的影响

近年来,随着激光、微弱信号测量以及瞬态测量技术等发展,对溶液中激发态离子的化学和物理行为的研究已日益受到人们的重视,激发态铀酰离子发光衰减的研究尤为活跃.Marcantonatos 等、Formosinho 等以及郑企克、王志麟等对高氯酸溶液中激发态铀酰离子的发光衰减过程进行了详细的研究.探讨了ClO_4~-溶液中pH 等对激发态铀酰离子的发光衰减的影响,观察到了一定的pH 条件下激发态铀(Ⅵ)的非单一指数衰减,并各自提出了不同的解释.值得提出的是,上述的一系列研究都是在高氯酸溶液中,其它体系中铀(Ⅵ)的发光哀减的研究进行得很少,报导则更少.1983年Joshi 等曾研究了80K 时SO_4~(2-)     

以苯甲酸正丁醇溶液萃取高氯酸氧鈾

本文研究苯甲酸的正丁醇溶液对高氯酸氧铀的萃取,测得苯甲酸在正丁醇和水相间的平衡常数(A=58),苯甲酸在鲍和正丁醇的水溶液中的电离常数(K_a=6.2×10~(-5))和萃取反应的平衡常数(K=6.4×10~(-5))。研究结果证明在水相中除UO_2~(2+)外,倚有UO_2A~+,UO_2A_2,UO_2(OH)~+和UO_2(OH)A共四种格合物(A~-表示苯甲酸根),其稳定常数经测定分别为:β_(10)=8.0×10~2,β_(20)=1.8×10~5,β_(01)=2.0×10~9,β_(11)=5.2×10~(12)。以上常数除K_α及β_(01)与文献值一致外,其余似尚无报告。交中提出一种较简便而较严谨的用萃取法测定混合型络合物的稳定常数的数据处理法。     

氟离子存在下铀与5—Br—PADCAP显色反应的研究及应用

研究了UO_2~(2+)-F~--5-Br-PADCAP体系的光度特性。结果表明,在pH 6.0～8.0,[F~-]/[UO_2~(2+)]=400～10000(摩尔比)范围内,试剂及配合物的最大吸收波长分别为456nm和580nm,UO_2~(2+)浓度在8～60μg/25ml范围内符合比耳定律,配合物的摩尔吸光系数为7.4×10~4,组成UO_2~(2+):F~-:R=1:3:1。将所确立的方法用于铀矿废水中铀含量的测定,结果令人满意。     

配位体SO2-4对激发态铀(VI)去活化的影响

The dependence of the luminescence decay of electronically excited uranyl ions on the concentrations of uranium and sulphate in aqueous solution has been investigated with a pulsed nitrogen laser as a light source and a programmable transient recorder for lifetime measurements. Single exponential decay of the Luminescence is observed. The deactivation process of the excited uranyl ions should include radiative, nonradiative, water quenching and uranium self quenching and the measured lumine-scenec lifetime inidcates the result of all these processes. The Luminescence lifetime of uranyl ions increases with increasing concentration of sulphate and becomes constant when the equilibrium concentration of sulphate reaches 3.0 mol·L~(-1). The dependence of the Luminesence lifetime is similar to that of the UO_2(SO_4)_3~(4-) formation. This phenomenon can be interpreted in terms of the fact that in aqueous solution uranyl ions exist as aquo-uranyl ions. As the concentration of sulphte increaes the water molecule of hydrated uranyl ions will be replaced by sulphate ions via complex formation, and the quenching of excited uranyl ions by water is reduced. The self quenccing and the water quenching rate constants of UO_2(H_2O)_6~(2+) and UO_2(SO_4)_3~(4-) are estimated. Based on the experimental results a model for the deactivation mechanism of excited uranyl ions in sulphate solution is proposed.     

Coordination of uranium(VI) with functional groups of bacterial lipopolysaccharide studied by EXAFS and FT-IR spectroscopy

The complexation of uranyl ions with lipopolysaccharide (LPS), the main component of the cell wall of Gram-negative bacteria, was investigated on a molecular level with U L(III)-edge extended X-ray absorption fine structure (EXAFS) and attenuated total reflection Fourier transform infrared (ATR-FT-IR) spectroscopy over a wide pH range (2.6 to 7.0). For the first time, structural determinations of uranyl complexes with cell wall compounds were extended from acidic up to neutral pH. The main functionalities responsible for uranyl binding are phosphoryl and carboxyl groups. At an excess of LPS, related to environmental conditions, the uranyl ion is mainly complexed by phosphoryl groups four-fold monodentately coordinated in the equatorial plane of the uranyl dioxo cation UO(2)(2+) showing great homologies to the uranyl mineral phase meta-autunite in the EXAFS spectra. At equimolar ratios of uranyl and functional groups of LPS, according to a slight deficit of phosphoryl groups, additional carboxyl coordination in a bidentate manner becomes important as it is shown by IR spectroscopy. From the vibrational spectra, a mixed coordination of UO(2)(2+) with both phosphoryl and carboxyl groups is derived. The coordination of uranyl ions to the LPS molecule is obviously mainly controlled by the U/LPS concentration ratio, and the influence of pH is only of minor significance at the investigated range.     

Theoretical investigation of uranyl dihydroxide: oxo ligand exchange, water catalysis, and vibrational spectra

Density functional theory is employed to investigate uranyl dihydroxide, UO2(OH)2, isomerization reaction energy barriers, including those occurring via proton shuttles. The ground-state structure of a uranyl dihydroxide complex containing a uranyl moiety with a near 90 degrees O=U=O bond angle is reported for the first time. Furthermore, we predict the vibrational spectra of these compounds. Scalar-relativistic effects for uranium are treated by employing a relativistic effective core potential.     

pH dependence of uranyl retention in a quartz/solution system: an XPS study

We have investigated the pH dependence of U(VI) retention in quartz/10(-4) M uranyl solution systems, under conditions favoring formation of polynuclear aqueous species and of colloids of amorphous schoepite as U(VI) solubility-limiting phases. X-ray photoelectron spectroscopy was used to gain insights into the coordination environments of sorbed/precipitated uranyl ions in the centrifuged quartz samples. The U4f XPS spectra made it possible to identify unambiguously the presence of two uranyl components. A high binding energy component, whose relative proportion increases with pH, exhibits the U4f lines characteristic of a reference synthetic metaschoepite. Such a high binding energy component is interpreted as a component having a U(VI) oxide hydrate character, either as polynuclear surface oligomers and/or as amorphous schoepite-like (surface) precipitates. Its pH dependence suggests that a binding of polynuclear species at quartz surfaces and/or a formation of amorphous schoepite-like (surface) precipitates is favored when the proportion of aqueous polynuclear species increases. A second surface component exhibits binding energies for the U4f core levels at values significantly lower (DeltaE(b)=1.2 eV) than for metaschoepite, evidencing uranyl ions in a distinct coordination environment. Such a low binding energy component may be attributed to monomeric uranyl surface complexes on the basis of published EXAFS data. Such a hypothesis is supported by a major contribution of the low binding energy component to the U4f XPS spectra of reference samples for uranyl sorbed on quartz from very acidic 10(-3) M uranyl solutions where UO(2)(2+) ions predominate.     

STUDY OF LUMINESCENT FORMS OF THE URANYL ION

Luminescence spectra and luminescence decay kinetics of uranyl sulphate water and uranyl nitrate acetone solutions of different concentrations have been studied. Similar experiments have been done with uranyl sulphate powder under vacuum. It has been experimentally shown that the hydrolysis of uranyl sulphate in water takes place, and under low salt concentrations (0.1-4.0 times 10^-4 M) a luminescence of a basic form of the photoexcited ion with a tentative structure of UO₂OH⁺* has been observed. The luminescence of the acidic form UO⁺* has been observed under higher salt concentrations (1–4 times 10^-2 M) in water and under any salt concentration in acetone. The acidic form has the characteristic emission spectrum possessing vibrational structure. The luminescence concentrational quenching of both photoexcited uranyl forms and exciplex emission have not been observed. The effect of a number of organic quenchers and molecular oxygen on uranyl luminescence has been studied. There is no luminescence quenching by O₂ up to 2 times 10⁶ Pa (20 atm) pressure. The low effectiveness of energy transfer from the photoexcited uranyl forms has been explained in terms of strong steric screening of 5f-uranium (VI) orbital by oxygen atoms and by external filled up uranium electronic shells.     

Aqueous coordination chemistry and photochemistry of uranyl(VI) oxalate revisited: a density functional theory study

Using density functional theory (DFT) calculations, we revisited a classical problem of uranyl(VI) oxalate photochemical decomposition. Photoreactivities of uranyl(VI) oxalate complexes are found to correlate largely with ligand-structural arrangements. Importantly, the intramolecular photochemical reaction is inhibited when oxalate is bound to uranium exclusively in chelate binding mode. Previously proposed mechanisms involving a UO(2)(C(2)O(4))(2)(2-) (1:2) complex as the main photoreactive species are thus unlikely to apply, because the two oxalic acids are bound to uranium in a chelating binding mode. Our DFT results suggest that the relevant photoreactive species are UO(2)(C(2)O(4))(3)(4-) (1:3) and (UO(2))(2)(C(2)O(4))(5)(6-) (2:5) complexes binding uranium in an unidentate fashion. These species go through decarboxylation upon excitation to the triplet state, which ensues the release of CO(2) and reduction of U(vi) to U(v). The calculations also suggest an alternative intermolecular pathway at low pH via an electron transfer between the excited state *UO(2)(2+) and hydrogen oxalate (HC(2)O(4)(-)) which eventually leads to the production of CO and OH(-) with no net reduction of U(VI). The calculated results are consistent with previous experimental findings that CO is only detected at low pH while U(IV) is detected only at high pH.     

Laser-induced luminescence of barite after thermal treatment

The photoluminescence (PL) of barite is a noncharacteristic property and cannot be used for the investigation of its structure. After thermal treatment of barite at 600°C several luminescent centers were observed, providing information about different impurities. UO ₂ ²⁺ was determined from the vibrational structure and the long decay time of the luminescence band. Two different types of uranyl were detected, thin films of uranyl mineral (most probably, reserfordin) and a solid solution of uranyl ion in barite crystal. Characteristic green luminescence of UO ₂ ²⁺ may be used as indicative feature for the prospecting of uranium deposits and for the sorting of barite ores with the aim of cleaning from harmful U impurities. Eu²⁺ was determined from the spectral position, the half-width and the characteristic decay time of the luminescence band. Mn²⁺ and Ag⁺ were determined by comparing luminescence bands spectral parameters to those of synthesized BaSO₄−Mn and BaSO₄−Ag. Fe³⁺ or Mn⁴⁺ were determined from the spectral-kinetic parameters of the luminescence bands. Dedicated to Professor Lisa Heller-Kallai on the occasion of her 65^th birthday     

Sorption profile and chromatographic separation of uranium (VI) ions from aqueous solutions onto date pits solid sorbent

The retention profile of uranium (VI) as uranyl ions (UO(2)(2+)) from the aqueous media onto the solid sorbent date pits has been investigated. The sorption of UO(2)(2+) ions onto the date pits was achieved quantitatively (98+/-3.4%, n=5) after 15 min of shaking at pH 6-7. The sorption of UO(2)(2+) onto the used sorbent was found fast, followed by a first order rate equation with an overall rate constant, k of 4.8+/-0.05 s(-1). The sorption data were explained in a manner consistent with a "solvent extraction" mechanism. The sorption data were also subjected to Freundlich isotherm model over a wide range of equilibrium concentration (1-20 microgmL(-1)) of UO(2)(2+). The results revealed that, a "dual-mode" of sorption mechanism involving absorption related to "solvent extraction" and an added component for "surface adsorption" is most likely operated simultaneously for uranyl ions uptaking the solid sorbent. The thermodynamic parameters (-DeltaH, DeltaS and DeltaG) of the uranyl ions uptake onto the date pits indicated that, the process is endothermic and proceeds spontaneously. The interference of some diverse ions on the sorption UO(2)(2+) from the aqueous media onto the date pits packed column was critically investigated and the data revealed quantitative collection of UO(2)(2+) at 5 mLmin(-1) flow rate. The retained UO(2)(2+) was recovered quantitatively with HCl (3.0 molL(-1)) from the column at 5 mLmin(-1) flow rate. The mode of binding of the date pits with UO(2)(2+) was determined from the IR spectral date bits before and after extraction of uranium (VI). The height equivalent (HETP) and the number (N) of theoretical plates of the date pits packed column were determined from the chromatograms. Complete retention and recovery of UO(2)(2+) spiked to wastewater samples by the date pits packed column was successfully achieved. The capacity of the used sorbent towards retention of uranium (VI) from aqueous solutions was much better than the most common sorbents.     

钠盐溶液中U(Ⅵ)的电化学电子转移与晶化研究

采用循环伏安法分析钠盐溶液中U(Ⅵ)的电化学行为,恒电位电化学还原处理U(Ⅵ),利用交流阻抗谱分析电化学还原反应中的过程动力学特性,利用X射线衍射、扫描电子显微镜和电子能谱等方法分析了U(Ⅵ)的电化学晶化.结果表明,在钠盐溶液中,U(Ⅵ)可通过电化学反应先还原成低价的U(V)并进一步还原为U(Ⅳ),U(Ⅳ)一步氧化为U(Ⅵ),U(Ⅳ)/U(Ⅵ)之间的电化学转化过程受扩散控制,且U(Ⅵ)的电化学电子转移易受环境p H值的影响;恒电位还原4 h时,溶液中U(Ⅵ)的去除率可达90%,U(Ⅵ)的结晶固化产物主要以固态的(UO2)6O2(OH)8·6H2O(水铀矿)和UO2的形式附着在工作电极上.