CO2 conversion to phenyl isocyanates by uranium(vi) bis(imido) complexes.

Uranium(vi) trans-bis(imido) complexes [U(κ4-{(tBu2ArO)2Me2-cyclam})(NPh)(NPhR)] react with CO2 to eliminate phenyl isocyanates and afford uranium(vi) trans-[O[double bond, length as m-dash]U[double bond, length as m-dash]NR]2+ complexes, including [U(κ4-{(tBu2ArO)2Me2-cyclam})(NPh)(O)] that was crystallographically characterized. DFT studies indicate that the reaction proceeds by endergonic formation of a cycloaddition intermediate; the secondary reaction to form a dioxo uranyl complex is both thermodynamically and kinetically hindered

Cloud Point Extraction and Spectrophotometric Determination of Uranium (VI) in Water Samples after Mixed Micelle-Mediated Extraction Using Chromotrope 2R as Complexing Agent

A rapid, selective and sensitive method for the preconcentration and determination of uranium (VI) by cloud point extraction (CPE) was developed. The method was based on the color reaction of 5.00 ng mL−1 uranium (VI) with 1.5×10−4 mol L−1 of chromotrope 2R in the presence of 0.015 mol L−1 potassi-um iodide at pH 8 in HEPES buffer and mixed micelle-mediated extraction of complex. The mixture of a nonionic surfactant (0.2 % (v/v) of (Triton X-114) and a cationic (2.0×10−4 mol L−1 of CTAB) was utilized as a suitable micellar medium for preconcentration and extraction of uranium (VI) complexes. Effect of extraction and reaction parameters was studied and optimum parameters were established. The analytical characteristics of the method (e.g. linear range, limit of detection, preconcentration and improvement factors) were obtained. Linearity was obeyed in the range of 0.2−10 ng mL−1 of uranium (VI) with a detection limit of 0.035 ng mL−1. The diverse ion effect of some anions and cations on the extraction efficiency of target ions was tested. The proposed method was successfully applied for the determination of uranium (VI) in various water samples. (doi: 10.5562/cca1922

Electrochemical Redox Processes of Uranium In Aqueous Solutions of Acetylacetone

Electrochemical redox processes of uranium (VI) and uranium (V) in aqueous solutions of acetylacetone have been studied by means of various electrochemical techniques. The presence of acetylacetone accelerates the rate of disproportionation of uranium (V), even under conditions such that uranium (VI) is not in the form of the acetylacetonato complex. The corresponding rate constants of disproportionation were determined. The influence of the acetylacetonato ion concentration on the potential and on the rate of the uranium (VI) - uranium (V) electron transfer was investigated by means of cyclic voltammetry and squa,re-wave polarography. Both reduction and oxidation of uranium (V) were investigated by using the Kalousek commutator technique. A mechanism for those processes is proposed. It was proved by electrocapillary measurements that besides the adsorption of acetylacetone, adsorption of several uranium acetylacetonato species plays an important role in the overall mechanism. Taking into account the experimental results, the redox processes of uranium (VI) and uranium (V) in the presence of acetylacetone can be explained in terms of an ECE mechanism

Removal of uranium (VI) from aqueous solution by acid modified zeolites

Cilj ovog rada je prikaz mogućnosti primene prirodnog i modifikovanog zeolitskog minerala kao adsorbenta i materijala za sanaciju voda kontaminiranih uranijum jonom. Modifikovani uzorci zeolita dobijeni su tretiranjem prirodnog zeolita - klinoptilolita sa kiselinama: hlorovodoničnom, oksalnom i limunskom. Polazni i modifikovani zeoliti su okarakterisani hemijskom analizom, skenirajućom elektronskom mikroskopijom (SEM), rendgenskom analizom (XRPD), IC spektroskopijom, termičkom (TG/DTA) analizom i određivanjem kapaciteta katjonske izmene, a polazne i neadsorbovane količine uranijum jona su određene fluorimetrijski. Eksperimenti su sprovedeni da se ispita uticaj odnosa čvrsto/tečno, pH i vremena na adsorpciju uranijum jona na zeolitu. Utvrđeno je da tretman sa kiselinama zeolita povećava adsorpciju uranijum jona. Najviši indeks adsorpcije imao je uzorak zeolita modifikovan sa hlorovodoničnom kiselinom. Dobijeni rezultati adsorpcije na H-zeolitu su izračunati prema Langmirovom modelu. Projekat MPNTR, br. 142057 Razvoj stakala sa kontrolisanim otpuštanjem jona za primenu u poljoprivredi i medicini (MPNTR - 34001)The objective of this study was the review of natural zeolite, modified with acid, as a candidate material for the remediation of groundwater contaminated by uranium(VI). The modified zeolite samples were obtained by treatment of natural zeolite - clinoptilolite with acids: hydrochloric, oxalyc and citric. Starting and modified zeolites were characterized by chemical analysis, SEM, XRPD analysis, IR spectroscopy, thermal (TG/DT) analysis and by determination of cation exchange capacity, while starting and nonadsorbed amounts of uranium(VI) ion were determined by fluorometric method. Batch experiments were conducted to investigate the effect of solid/liquid ratio, pH and time on the U(VI) uptake by zeolite. Modification of zeolitic tuff with acids significantly increased adsorption of uranium(VI). The highest adsorption of uranium(VI) ion was achieved on clinoptilolite modified with hydrochloric acid. Uranium(VI) adsorption data for zeolite modified with hydrochloric acid was fitted to the Langmuir model. Projekat MPNTR, br. 142057 The development of glasses with controlled ions release for application in agriculture and medicine (MESTD - 34001

Precipitation and hydrolysis of uranium(VI) in aqueous solutions: uranyl nitrate – potassium hydroxide

The precipitation and hydrolysis of uranium (VI) in aqueous Solutions of uranyl nitrate — potassium hydroxide — neutral electrolyte, was investigated. Clear and stable systems of uranyl nitrate and potassium hyđroxide, were studied, in equivalent concentration of 2 X10-3 N. The pH value, of the mentioned system was between 5 and 6. By addition of neutral electrolytes (potassium, calcium, strontium, barium, yttrium, and lantanum nitrate) the precipitation process was initiated and up to 70% of the uranium present was precipitated. The experimental results showed, that the precipitation of uranium (VI), in the observed system, was accomplished by several mechanisms, t.e. hydrolysis, coagulation, and formation of mixed uranates

Electrochemical Reduction of Uranium (VI) to Uranium (IV) in Carbonate Solutions

The purpose of this work was to investigate the possibility of preparation of uranium dioxide by electrochemical reduction of uranium(VI) from alkali carbonate solutions. There are many interesting features in deciding whether or not the electrochemical process is applicable to certain conditions of solution equilibria in the uranium-carbonate system. The study ·of the reduction of uranium(VI) from carbonate solutions has been undertaken to determine the reduction potential-current density relationship, the current efficiency, and the O/U ratio in the precipitated uranium dioxide, for which only scarce data are available in the literature

Влияние комплексообразователей на процессы сорбционной очистки вод, содержащих уран

Исследовано влияние комплексообразователей: динатриевых солей этилендиаминтетрауксусной кислоты (ЭДТА) и нитрилотриуксусной кислоты (НТА),уксусной кислоты (НАс), фульвокислот (ФК), карбоната натрия ( Na2CO3 ) на сорбцию U(VI) монтмориллонитом. Установлен сложный характер зависимости величин сорбции U(VI) от рН в присутствии комплексообразователей, что указывает на определяющую роль форм нахождения урана в очищаемыхводах. По величине влияния на процесс сорбции U(VI) монтмориллонитом исследованные комплексообразователи можно расположить в ряд: ЭДТА >НТА > Na2CO3 > HAc > ФК.Досліджено вплив комплексоутворювачів: динатрієвих солей етилендиамінтетраоцтової кислоти (ЕДТА) та нітрилотриоцтовоїкислоти (НТА), оцтової кислоти (НАс), фульвокислот (ФК), карбонату натрію (Na2CO3) на сорбцію U(VI) монтморилонітом. Встановлено складний характер залежності величин сорбції U (VI) від рН в присутності комплексоутворювачів, що вказує на визначальну роль форм знаходження урану y водах, що підлягають очистці. За величиною впливу на процес сорбції U(VI) монтморилонітом досліджені комплексоутворювачіможно розташувати в ряд: ЕДТА > НТА > Na2CO3 > HAc > ФК.Effect of complexing agents: ethylendiaminetetraacetic acid (EDTA) and nitrilotriacetic acid (NTA) disodium salts, acetic acid (HAc), fulvic acids (FA), sodium carbonate (Na2CO3) on the uranium (VI) sorption by montmorillonite was investigated. Complex character of dependence of uranium (VI) sorption values vs. pH in presence of complexing agents was established indicating important role of uranium species in waters under purification. It is possible to arrange complexing agents investigated according to magnitude of their effect on the uranium (VI) sorption by montmorillonite: EDTA > NTA > Na2CO3 > HAc > FA