Extraction Behaviour Of Uranium Research Articles

Insight Into the Influence of Ligand Conformation on Extraction Behaviour of Uranium: A Combined Theoretical and Experimental Study

Herein, two polymer-based solid-phase extraction materials, loading with urea monodentate ligand (UML) and biuret bidentate ligand (BBL) respectively, were newly synthesized. The influence of ligand conformation on uranium extraction was systematically studied for the first time. Our study indicates that the affinity of ligand for uranyl is determined by not only the coordinating atoms, coordination number and ligand structure, but also its conformation characteristics. The theoretical calculations reveal that (1) All 4 UML conformers and 12 BBL conformers are identified and divided into three types: having no hydrogen bond, having intramolecular CH center dot center dot center dot O=C bond, and having both intramolecular CH center dot center dot center dot O=C and NH center dot center dot center dot O=C bonds; (2) 4 coordinating-inactive BBL conformers are demonstrated with high fraction (> 99%) and lower coordination ability for uranium due to formation of the distinctive NH center dot center dot center dot O=C bond between coordinating oxygen and hydrogen of imino group in the same ligand (inactivation of coordinating atom), which significantly weaken the expected advantage of BBL on its ability to extract uranium; (3) Above inactivation may more easily exist in conformers of the structurally complicated multidentate ligand; and (4) Based on Boltzmann distribution and self-consistent-field calculations of electronic energies, the most probable paths of the two uranium extraction processes for UML- and BBL-based polymers, respectively, were obtained, which indicates that the extraction ability of BBL towards uranyl could not be obviously stronger than that of UML, resulting from nearly equal-values of Delta G (-28 kJ mol(-1) for UML, -30.8 kJ mol(-1) for BBL). The results show good agreement with the experimental results.

Influence of Co-Solvent on the Extraction Behaviour of Uranium and Thorium Nitrates with Organophosphorous Compounds

Supercritical Fluid Extraction (SFE) is emerging as a powerful technique in the extraction of metal ions. In the present study, the extraction of nitrates of uranium and thorium was carried out using supercritical carbon dioxide (Sc-CO2) modified with various organophosphorous compounds such as dialkylalkyl phosphonates, trialkyl phosphates and trialkyl phosphine oxides in the presence of co-solvents such as methanol, dichlormethane and n-hexane. The influence of ligand and co-solvent on the extraction of the metal nitrates was studied in detail. These studies have established that co-solvent plays an important role in the extraction as well as fractionation of uranium and thorium nitrates. Polar co-solvent, methanol provided faster extraction without fractionation whereas the non-polar solvent, e.g. n-hexane provided some fractionation of metal nitrates though the extraction kinetics was slower.

Development of Alternate Extractants for Separation of Actinides

Selection of an extractant plays a key role in the development of a commercial solvent extraction process. Though tri- n-butyl phosphate (TBP) is currently used as the extractant for the processing of fast reactor fuel, there is a need to introduce an alternate extractant to ensure the success of closing the fast reactor fuel cycle in India. Recent studies undertaken in our laboratory for the identification of the most suitable extractant for fast reactor fuel reprocessing are addressed in this paper. Studies carried out on the influence of alkoxy groups of dialkylalkyl phosphonates on the extraction behaviour of uranium and thorium is also discussed.

Extraction of the uranyl ion with 3-phenyl-4-benzoyl-5-isoxazolone (HPBI) and neutral donors from dilute nitric acid medium

Abstract The extraction behaviour of Uranium (VI) from aqueous nitric acid medium employing 3-phenyl-4-benzoyl-5-isoxazolone (HPBI) has been studied in the presence of various amides, e.g , di-2-ethylhexylacetamide (D2EHAA), di-2-ethylhexylpropanamide (D2EHPrA), di-2-ethylhexylisobutylamide (D2EHiBA) and di-2-ethylhexylpivylamide (D2EHPvA) in toluene medium. The extraction constant (log k ex) for the binary species UO2(PBI)2·nH2O was found to be 1.42±0.14 which is by far the largest amongst the corresponding values known for the other β-diketones. The overall equilibrium constant (log K) for the ternary species UO2(PBI)2·D2EHAA, UO2(PBI)2·D2EHPrA, UO2(PBI)2·D2EHiBA and UO2(PBI)2·D2EHPvA were estimated to be 6.51, 6.21, 6.11 and 5.77 respectively. This trend in equilibrium constants was in accordance with the substitution of the amides as sterically crowded amides show relatively lower equilibrium constant values. The extraction constants follow an inverse correlation with the pK a values of the β-diketonates while the equilibrium constants vary linearly with the size of the amides. The steric factors have been found to play a significant role in the co-ordination of the amides to the uranyl β-diketones when the carbonyl group is a part of the heterocyclic ring. The distribution ratios of the metal were measured in the temperature range 15 to 52 °C using each of the amide donors in combination with HPBI. Calculation of enthalpy and entropy therefrom indicated that the extraction was thermodynamically favoured process and maximum extraction resulted in the case of UO2(PBI)2·D2EHAA.

Solvent extraction of uranium(VI) and thorium(IV) from nitrate media by Cyanex 923

The extraction behaviour of uranium(VI) and thorium(IV) from nitrate solutions has been investigated using Cyanex 923 (TRPO) in xylene as an extractant. The extraction data have been analyzed by both graphical and theoretical methods by taking into account complexation of the metal ion in the aqueous phase with inorganic ligands and all plausible complexes extracted into the organic phase. The results demonstrate that these metal ions are extracted into xylene as Th(NO3)4 · 2 TRPO and UO2(NO3)2 · 2 TRPO. The equilibrium constants of the extracted complexes have been deduced by non-linear regression analysis. Infrared spectral data of the extracted complexes have been used to further clarify the nature of the complexes. The selectivities between these metal ions were evaluated and compared with commercially important extractants like tri-n-butylphosphate (TBP).

Solvent extraction of uranium(VI) into toluene by dicyclohexano-18-crown-6 from mixed aqueous-organic solutions

Extraction behaviour of uranium(VI) from mixed organo-aqueous solutions containing water-miscible protic aliphatic alcohols and several aprotic solvents was investigated by using dicyclohexano-18-crown-6(DC18C6) as an extractant. The organic phase was a binary solution of DC18C6 and toluene while the polar phase was a three component solution of uranyl nitrate, polar additive and aqueous nitric acid. Methanol, ethanol, isobutanol, dioxane, acetone, propylene carbonate and acetonitrile were used as the organic components of the mixed (polar) phase. Propylene carbonate, acetone, acetonitrile and dioxane increased the extractability of U(VI), whereas alcoholic additives showed only an antagonistic effect. The relative increase in extraction was found to be more at lower nitric acid concentrations. Possible reasons for such behaviour are briefly discussed. Recovery of U(VI) from loaded organic phase was easily accomplished using dilute perchloric acid and sulphuric acid. A sample method was standardized for the separation of plutonium(IV) from uranium(VI) based on its reductive stripping.

Inorganic solvent extraction data of some elements including uranium, thorium and plutonium

The extraction behaviour of uranium, thorium, plutonium and alkali and alkaline earth metals from hydrochloric, nitric and sulphuric acid solutions with technical high-molecular-weight amines and tributylphosphate has been investigated. The investigation of the change of the distribution coefficients with changes in the acid and amine concentrations lead to the conclusion that under the conditions employed some elements mentioned above were extracted with high K d values and others not.

Analytical Extraction of Uranium with TOPO from Sea Water

Abstract A distribution study was carried out on the extraction behaviour of uranium in sea water using solutions of TOPO in cyclohexane. The influence of various factors (time, pH, TOPO concn in the organic phase, nitrate or chloride concentration in the aqueous phase and volumetric ratio between the two phases) on the extractability of uranium was investigated. In view of the results obtained, the best conditions for a quantitative recovery were selected. The application of the results to fluorimetric determination of uranium is also reported.

Extraction behaviour of uranium, zirconium and ruthenium with gamma-irradiated sulfoxides and tri-n-butyl phosphate

The extraction, scrubbing and stripping behaviour of uranium, zirconium and ruthenium with di-n-hexyl and di-n-octyl sulfoxides in Solvesso-100 and tri-n-butyl phosphate (TBP) in shell Sol-T irradiated by various gamma doses (0–169 Mrads) have been investigated. 2M HNO3 was used for extraction and scrubbing and 0.01M HNO3 for stripping purposes. Results indicate that the extraction of uranium with TBP increases and that with sulfoxide decreases with dose. This is reflected in their corresponding scrubbing percentages too. The stripping percentage of uranium with TBP decreases with dose while the reverse is the case with sulfoxide. The extraction of zirconium with TBP increases sharply with dose as compared to sulfoxides. The extraction scrubbing and stripping of ruthenium remain almost unaffected by dose both in the case of TBP and sulfoxides. These results lead to much higher overall decontamination factors for uranium with respect to zirconium as well as ruthenium with irradiated sulfoxides as compared to those with irradiated TBP.

Extraction of uranium(IV) and uranium(VI) by primary and tertiary-amines from sulphate solutions

In developing a method for possible low level isotopic enrichment, which uses to advantage the equilibrium isotope effect observed during U(1V)-U(VI) electron exchange reaction in sulphate solutions, details of a solvent extraction process involving high concentration of a mixture of U(IV) and U(VI) and at low acid concentrations, are described. The extraction behaviour of uranium under these conditions is discussed. During the extraction with amines, U(IV) tended to get oxidised in sulphate solutions.