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.     

Spectrophotometric determination of zirconium, uranium, thorium and rare earths with arsenazo III after extractions with thenoyltrifluoroacetone and tri-n-octylamine

A method is described for the spectrophotometric determination of microgram amounts of zirconium, uranium(VI), thorium and rare earths with Arsenazo III after systematic separation by extraction. First zirconium is extracted into a xylene solution of thenoyltrifluoroacetone (TTA) from about 4M hydrochloric acid. Uranium(VI) is then extracted into a xylene solution of tri-n-octy lamine from about 4M hydrochloric acid. Thorium is next extracted into TTA solution at pH about 1.5, and finally rare earths are extracted into TTA solution at pH about 4.7. Each metal is back-extracted from the organic phase before determination.     

Extraction behavior of uranium,plutonium and some fission products with gamma-irradiated N,N′-dialkylamides

The extraction behavior of uranium(VI), plutonium(IV) and fission products like zirconium, ruthenium and europium from 3.5M nitric acid medium with gamma-irradiated dibutyl derivatives of hexanamide (DBHA), octanamide (DBOA) and decanamide (DBDA) in dodecane has been investigated as a function of absorbed dose up to 184 MRads. The results indicate that the K_d value for extraction of uranium(VI) decreases gradually, while K_d for extraction of plutonium(IV) decreases rapidly with dose up to 35 MRads, increasing thereafter with dose, indicating synergistic effects of radiolytic products at higher doses. Ruthenium and europium are not extracted in the entire dose range up to 184 MRads, while extraction of zirconium(IV) increases steadily up to 50 MRads and increases radiply thereafter, indicating synergistic effect of radiolytic products similar to that of plutonium(IV) beyond a dose of 50 MRads. The extractability of uranium(VI) and plutonium(IV) with 1M dibutyl decanamide (DBDA) in dodecane was studied for uranium loading up to 75 mg/ml and plutonium loading up to 3 mg/ml. The percent extraction was found to vary from 91 to 71 for uranium and 95 to 89 for plutonium, respectively. Quantitative stripping of uranium can be achieved with 0.01M nitric acid and plutonium with 0.5M nitric acid and 0.05M hydroxylamine soluton in two steps from an organic phase loaded with 53.2 mg/ml of uranium.     

Liquid-liquid extraction separation of uranium(VI) from associated elements using dibenzo-24-crown-8 from hydrobromic acid medium

Liquid-liquid extraction of uranium (VI) from hydrobromic acid solutions with dibenzo-24-crown-8 in nitrobenzene have been investigated. Uranium(VI) was quantitatively extracted from 6.0–8.0M hydrobromic acid with 0.001–0.01M dibenzo-24-crown-8 and was quantitatively stripped from the organic phase with 0.1–1.0M hydrochloric acid, 0.5–10M nitric acid, 2–10M perchloric acid, 3.0–10M sulfuric acid or 3.0–10M acetic acid. It was possible to separate uranium(VI) from a number of elements in binary mixtures. Most of the elements showed very high tolerance limit Uranium(VI) was also separated from a number of associated elements in multicomponent mixtures. The method is very simple, selective, rapid and highly reproducible (approximately±2%) and was applied to the analysis of uranium in geological samples.     

Distribution of Pu(VI) from nitric acid to tri-n-butyl phosphate saturated with uranium(VI)

Solvent extraction of plutonium(VI) from nitric acid (1 to 5M) into 20% and 30% TBP in dodecane saturated with uranium(VI) (0% to 80%) has been studied. For a particular nitric acid concentration, the distribution coefficient (K _d ) is found to decrease with the increase in saturation of organic phase with uranium(VI). At a fixed organic phase the saturationK _d increased with increase in nitric acid concentration, however, the magnitude of this increase inK _d decreased with the increase in saturation.     

Homogeneous liquid-liquid extraction of uranium(VI) using tri-n-octylphosphine oxide.

A simple and efficient method for the selective separation and preconcentration of uranium(VI) using homogeneous liquid-liquid extraction was developed. Tri-n-octylphosphine oxide (TOPO) and tri-n-butylphosphate (TBP) were investigated as complexing ligands, and perfluorooctanoate ion (PFOA-) was applied as a phase separator agent under strongly acidic conditions. Under the optimal conditions ([PFOA-] = 1.7 x 10(-3) M, [TOPO] = 5.4 x 10(-4) M, [HNO3] = 0.3 M, [acetone] = 3.2% v/v) 10 microg of uranium in 40 ml aqueous phase could be extracted quantitatively into 8 microl of the sedimented phase. The maximum concentration factor was 5000-fold. However, an effort for the quantitative extraction using TBP was inefficient and the percent recovery was at most 56.7. The influence of the type and concentration of acid solution, optimum amount of the ligand, type and volume of the organic solvent, concentration of PFOA, volume of the aqueous sample and effect of different diverse ions on the extraction and determination of uranium(VI) were investigated. The proposed method was applied to the extraction and determination of uranium(VI) in natural water samples.     

Extraction of certain actinide and lanthanide elements from different acid media by polyurethane foams loaded with di(2-ethylhexyl)phosphoric acid (HDEHP)

The extraction of uranium(VI) from an aqueous HNO₃ phase into an organic phase consisting of a polyurethane foam immobilizing a solution of di(2-ethylhexyl)phosphoric acid (HDEHP) in o-dichlorobenzene has been investigated at varying concentrations of nitric acid and HDEHP. The mechanism of the extraction is discussed on the basis of the results obtained. The aggregation number of HDEHP immobilized on the foam was obtained from the analysis of data obtained for the extraction of cerium(III) from acidic perchlorate solutions of constant ionic strength.     

Separation and spectrophotometric determination of uranium(VI) by extraction with tri-n-octylphosphine oxide and benzophenone

Uranium(VI) is separated by extraction from nitric acid medium into a molten mixture of tri-n-octylphosphine oxide and benzophenone at about 50°. The organic phase solidifies on cooling and is separated and dissolved in ethanol. The uranium(VI) in this solution is then determined spectrophotometrically with 1-(2-pyridylazo)-2-naphthol.     

Extraction of uranium(VI) and thorium(IV) from nitric acid solution by N-alkylcaprolactam

Extraction of uranium(VI), thorium(IV) from nitric acid has been studied with N-octylcaprolactam and N-(2-ethyl)hexylcaprolactam. Distribution coefficients of U(VI), Th(IV) and HNO₃ as a function of aqueous NHO₃ concentration, extractant concentration and temperature have been studied. The compositions of extracted species, thermodynamic parameters of extraction have been evaluated. Third phase formation in extraction of U(VI) has been studied. Back extraction behavior of U(VI) and Th(IV) from the organic phase has also been tested. The results obtained are compared with those obtained by using TBP under the same experimental conditions.     

Further study of extraction equilibrium of uranium(VI) with dicyclohexano-18-crown-6 and its application to separating uranium and thorium

In our publication (1), the extraction of uranium with dicyclohexano-18-crown-6 (mixed isomers) has been described. The extraction equilibrium of uranium(VI) from aqueous hydrochloric acid solution with dicyclohexano-18-crown-6 isomer A (Ia) and isomer B (Ib) in 1,2-dichloroethane is presented in this paper. The extracted species are found to be 1:2 (metal/crown) for Ia and 2:3 for Ib from slope analysis and direct determination of extracted complexes. The extraction equilibrium constants (Kex) have been determined at 25°C, and equal 29.5 for the former and 0.208 for the latter. It is concluded that Ia has stronger coordinate ability for uranium than Ib. The different orientation of the lone pairs of the oxygen atoms in both isomers will be taken into account for interpreting above results. The extraction of uranium(VI) with dicyclohexano-18-crown-6 (mixed isomers) or Ia from aqueous hydrochloric acid solution is effective and selective. In 0.1M crown ether-1,2-dichloroethane-6N HCl system, the separation factor U(VI)/Th(IV) exceeds 1000. The result can be taken in separating uranium and thorium.     

Investigation of Uranium(VI) Extraction Mechanisms from Phosphoric and Sulfuric Media by 31P-NMR

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.     

Extraction of uranium(VI) from nitric acid medium by 1.1M tri-n-butylphosphate in ionic liquid diluent

Summary A systematic study on the extraction of U(VI) from nitric acid medium by tri-n-butylphosphate (TBP) dissolved in a non-traditional diluent namely 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF₆) ionic liquid (IL) is reported. The results are compared with those obtained using TBP/n-dodecane (DD). The distribution ratio for the extraction of U(VI) from nitric acid by 1.1M TBP/bmimPF₆ increases with increasing nitric acid concentration. The U(VI) distribution ratios are comparable in the nitric acid concentration range of 0.01M to 4M, to the ratios measured using 1.1M TBP/DD. In contrast to the extraction behavior of TBP/DD, the D values continued to increase with the increase in the concentration of nitric acid above 4.0M. The stoichiometry of uranyl solvate extracted by 1.1M TBP/IL is similar to that of TBP/DD system, wherein two molecules of TBP are associated with one molecule of uranyl nitrate in the organic phase. Ionic liquid alone also extracts uranium from nitric acid, albeit to a small extent. The exothermic enthalpy accompanying the extraction of U(VI) in TBP/bmimPF₆ decreases with increasing nitric acid and with TBP concentrations.     

Extraction of technetium(VII) from uranium(VI) in nitric acid system by primary amine — n-heptane solution

Separation of technetium(VII) from uranium(VI) has been studied through experiments on the coprecipitation of technetium(VII) with precipitation of ammonium diuranate, and on the extraction of technetium(VII) from a 3M aqueous nitric acid solution using, as extractant, a primary amine (Primene JMT) dissolved in either chloroform or n-heptane solution. Ammonium diuranate precipitation proved to provide the most satisfactory means of separating technetium(VII) from uranium(VI) in solution. Extraction of technetium(VII) contained in nitric acid solution using Primene JMT dissolved in n-heptane solution proved to be quantitative after several cycles of the procedure and alternatively, upon raising to 51 the volume ratio between the organic phase containing the extractant and the aqueous phase containing technetium(VII). Stripping of technetium(VII) into 2M aqueous ammonium carbonate solution was enhanced to quantitative level by repetition of the stripping procedure, and alternatively, by adding the ammonium carbonate in a volume ratio of 51 with respect to the organic phase containing technetium(VII).     

Determination of major,minor and trace elements in Iraqi vegetable samples by INAA

Our aim was to discover a method of separating zirconium(IV) and uranium(VI) from solutions. It is known that Zr(IV) and U(VI) are effectively extracted by tertiary amines from weak acidic sulfate solutions but the possibility of extraction decreases with increasing acidity. The transition from tertiary amine to primary amine Primene JMT enables the extraction of Zr also from more acidic solution. If both Zr and U are present in an aqueous solution, Zr is extracted preferentially and only the free part of the amine can convert uranium to an extract. The separation described below was carried out by preferentially stripping zirconium from the organic phase. The application of nitrate solution (2M HNO₃) to eliminate Zr from the solvent was tested. This method does not demand any special regeneration of the extraction agent and the amine nitrate, formed in the organic phase, can be used for further extraction of Zr without modification. Using this method of separation, a solution for producing pure ZrOCl₂·8H₂O was obtained.     

Solvent extraction separation of uranium(VI) with dibenzo-24-crown-8

Uranium(VI) was quantitatively extracted with 0.01M DB-24-crown-8 in nitrobenzene from 6 to 10M hydrochloric acid. From the organic phase uranium was stripped with 2M nitric acid and determined spectrophotometrically with PAR at 530 nm. Uranium(VI) was separated from a large number of elements in binary mixtures as well as from multicomponent mixtures. The method was extended to the analysis of uranium in geological samples and animal bone.     

Successive complexometric determination of thorium and uranium in sulphuric acid media

A selective analytical extraction method for rapid successive complexometric determination of thorium(IV) and uranium(VI) in sulphuric acid media is described. The method is based on the extraction of thorium and uranium from sulphuric acid media with N-butylaniline or N-benzylaniline in chloroform. Both thorium and uranium are selectively and quantitatively extracted in the presence of ascorbic acid and EDTA. Most cations and anions do not interfere. The reduction of uranium(VI) with sodium dithionite at room temperature is rapid and quantitative and superior to that with ascorbic acid, which reduces uranium(VI) in boiling solution. The method is simple, rapid and accurate, and the experimental conditions are not highly critical.     

Method of separating uranium from iron and thorium

Acid leaching of uranium deposits is not a selective process. Sulfuric acid solubilizes iron(III) and half or more of the thorium depending on the mineralog of this element. In uranium recovery by solvent extraction process, uranium is separated from iron by an organic phase consisting of 10 vol% tributylphosphate(TBP) in kerosine diluent. Provided that the aqueous phase is saturated with ammonium nitrate or made 4–5 M in nitric acid prior to extraction. Nitric acid or ammonium nitrate is added to the leach solution in order to obtain a uranyl nitrate product. Leach solutions containing thorium(IV) besides iron are treated in an analogous fashion. Uranium can be extracted away from thorium using 10 vol% TBP in kerosine diluent. The aqueous phase should be saturated with ammonium nitrate and the pH of the solution lowered to 0.5 with sufficient amount of sulfuric acid. In other words, the separation of uranium and thorium depends on the way the relative distributions of the two materials between aqueous solutions and TBP vary with sulfuric acid concentration. Thorium is later recovered from the waste leach liquor, after removal of sulfate ions. Uranium can be stripped from the organic phase by distilled water, and precipitated as ammonium diuranate.     

Possible Options for Uranium-carbide SNF Processing

The dissolution of uranium carbide pods as surrogate of UC fuel was performed by adding calcium metal in nitric acid, individually or in conjunction with oxide WWER's fuel. Extraction tests realized with the solution coming from the dissolution of the uranium carbide pods under PUREX conditions demonstrated that the plutonium remained in the aqueous phase. According to literature, it was found that it is connected with the formation of water-soluble organic compounds during the disslution. Extraction test performed on solutions coming from the dissolution a mix of uranium-carbide and oxide fuel (WWER) showed a complete extraction of uranium and plutonium and no plutonium retention of in the organic phase at the stripping step.     

Extraction behavior of U(IV) from nitric acid medium using di-isodecyl phosphoric acid dissolved in dodecane

Solvent extraction of U(VI) with di-isodecyl phosphoric acid (DIDPA)/dodecane from nitric acid medium has been investigated for a wide range of experimental conditions. Effect of various parameters including nitric acid concentration, DIDPA concentration, temperature, stripping agents, and other impurities like rear earths, transition metal ion, boron, aluminum ion on U(VI) extraction has been studied. The species extracted in the organic phase is found to be UO₂(NO₃)(HA₂)·H₂A₂ at lower acidity (<3.0 M HNO₃). Increase in temperature lead to the decrease in extraction with the enthalpy change by ∆H = −16.27 kJ/mol. Enhancement in extraction of U(VI) from nitric acid medium was observed with the mixture of DIDPA and tri butyl phosphate (TBP). The stripping of U(VI) from organic phase (DIDPA–U(VI)/dodecane) with various reagents followed the order: 4 M H₂SO₄ > 5% (NH₄)₂CO₃ > 8 M HCl > 8 M HNO₃ > Water. High separation factors between U(VI) and impurities suggested that the use of DIDPA for purification of uranium from multi elements bearing solution.     

Liquid-liquid extraction of uranium(VI) from nitric acid solutions with bis(octylsulfinyl)ethane (BOSE)

The liquid-liquid extraction behavior of uranium(VI) from aqueous nitric acid with bis(octylsulfinyl)ethane (BOSE) in 1,1,2,2-tetrachloroethane has been studied over a wide range of conditions. The extracted species appears to be UO₂(NO₃)₂·2BOSE. It was found that the extraction increases with increasing nitric acid concentration up to 7 mol/l and then decreased. Extraction also increases with increasing extractant concentration. The influence of temperature and salting-out agent concentration on the extraction equilibrium and stripping of uranium(VI) was also investigated and the enthalpy of the extraction reaction was obtained.