Uptake of Pu(IV) on Bio-Rex 63 from nitric acid medium: A kinetic study

Back-extraction of tri- and tetravalent actinides from diisodecylphosphoric acid (DIDPA) is studied using hydrazine carbonate as back-extractant. In experiments using 0.5M DIDPA–0.1M TBP n-dodecane solution, Am(III), Eu(III), Pu(IV) and Np(IV) are back-extracted, and the distribution ratios are decreased with an increase of hydrazine carbonate concentration. The back-extraction equilibria are confirmed by slope analysis in consideration of neutralization between DIDPA and hydrazine carbonate, which occurs quantitatively during back-extraction. In particular, oxidation of Np(IV) to Np(V) during back-extraction is observed by measuring absorption spectra. The hydrazinium ion acts as an oxidation reagent in the back-extraction of Np(IV). Separation factors of those metals are compared with the results of HDEHP. Hydrazine carbonate back-extracts Np(IV) more selectively from DIDPA than from HDEHP.     

Determination of boron by (p, a) reaction

Back-extraction of tri- and tetravalent actinides from diisodecylphosphoric acid (DIDPA) is studied using hydrazine carbonate as back-extractant. In experiments using 0.5M DIDPA–0.1M TBP n-dodecane solution, Am(III), Eu(III), Pu(IV) and Np(IV) are back-extracted, and the distribution ratios are decreased with an increase of hydrazine carbonate concentration. The back-extraction equilibria are confirmed by slope analysis in consideration of neutralization between DIDPA and hydrazine carbonate, which occurs quantitatively during back-extraction. In particular, oxidation of Np(IV) to Np(V) during back-extraction is observed by measuring absorption spectra. The hydrazinium ion acts as an oxidation reagent in the back-extraction of Np(IV). Separation factors of those metals are compared with the results of HDEHP. Hydrazine carbonate back-extracts Np(IV) more selectively from DIDPA than from HDEHP.     

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.     

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

The effect of added TBP on the extraction of uranium(VI) with a solution of di-(2-ethylhexyl)-phosphoric acid (HDEHP) in o-dichlorobenzene from nitric acid solutions has been investigated at varying concentrations of nitric acid, HDEHP, TBP and uranium(VI). The mechanism of the synergistic effect of TBP is discussed on the basis of the results and can be summarized in the following equation: UO _2(aq) ²⁺ +0.67(HX)_3(o)+2TBP_(o)UO₂X₂·2TBP_(o)+2H _(aq) ⁺ where HX denotes HDEHP and the HDEHP loaded on the foam is trimerized.     

Extraction of Am(III) by mixture of dihexyl N,N-diethylcarbamoylmethyl phosphonate and tributyl phosphate in benzene from nitric acid solutions

Extraction of Am(III) by dihexyl N,N-diethylcarbamoylmethyl phosphonate (CMP) in benzene from nitric acid solutions (pH 2.0 to 6.0M) has been studied. High extraction of Am(III) by CMP from 2–3M HNO₃ was observed. The species extracted was found to be Am(NO₃)₃·3CMP. The extraction was also done with mixtures of CMP+TBP and CMP+TOPO, where mixed species were extracted in the organic phase. The back-extraction experiments gave an efficient back-extraction of Am(III) by pH 2.0 (HNO₃) from the loaded CMP+TBP phase but a poor back-extraction from the loaded CMP+TOPO phase. The loading of Nd(III) by mixture of CMP and TBP was 50% of the CMP concentrations at a total Nd(III) concentration of 0.182M. The thermodynamic parameters of Am(III) extraction by a mixture of CMP and TBP were evaluated by temperature variation method, which suggests that the two-phase reaction is stabilized by enthalpy and opposed by entropy.     

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 and separation of Th(IV) and U(VI) from nitric acid media using PIA-8 and HDEHP

Extraction behavior of Th(IV) and U(VI) has been investigated with bis(2-ethylhexyl) phosphinic acid (PIA-8) and bis(2-ethylhexyl) phosphoric acid (HDEHP) from nitric acid media in toluene. The optimum conditions for extraction of these metals have been established by studying various parameters like acid concentration, pH, reagent concentration, diluents and shaking time. The extraction of Th(IV) was found to be quantitative with 0.3-2.5M HNO₃ by 2.5^.10^-2M HDEHP and in the pH range 0.1-2.5 with 2.3^.10^-2M PIA-8 in toluene. U(VI) was completely extracted in the acidic range of 0.1-2.0M HNO₃ with 2.2^.10^-2M HDEHP and in the pH range of 1.0-3.0 with 2.0^.10^-2M PIA-8 in toluene. The probable extracted species have been ascertained by log D-log c plot as UO₂ R₂ ^.2HR with both the reagents and Th (NO₃)₂R₂ ^.2HR with PIA-8 and Th (NO₃)₃R^.3HR with HDEHP, respectively. Temperature dependence of the extraction equilibrium is examined by the temperature variation method. Separation of U(VI) and Th(IV) was also carried out from commonly associated metals.     

Abtrennung des Uran(IV) aus in der Kerntechnik anfallenden Lösungen mittels Extraktionschromatographie

Zusammenfassung Die extraktionschromatographische Abtrennung von Uran(IV) aus salpetersauren Lösungen wird beschrieben. Kolonnen mit Di-(2-äthylhexyl)-phosphorsäure (HDEHP) in Xylol als stationärer Phase wurden verwendet. Bei alleiniger Anwesenheit von Uran(IV) und Uran(VI) genügte es, mit Salpetersäure/0,1-m Hydrazin zu eluieren. Aus Lösungen komplexerer Zusammensetzung, die neben Uran(IV) und Uran(VI) auch noch längerlebige Spaltprodukte (¹⁴⁴Ce,¹⁰⁶Ru,⁹⁵Nb und¹³⁷Cs), Plutonium (III) und Korrosionsprodukte von Stahl [Fe(III), Co(II), Ni(II) und Cr(III)] enthielten, wurde das Uran(IV) auf zwei Arten abgetrennt. Bei der ersten Variante wurde es durch 5%iges HDEHP in Xylol an der Kolonne festgehalten und alle Begleitionen mit 2-n Salpetersäure/0,1-m Hydrazin entfernt. Bei der zweiten Variante konnte neben dem Uran (IV) auch das Uran(VI) in einer gesonderten Fraktion aufgefangen werden. Als stationäre Phase wurde 30%iges HDEHP, als Elutionsmittel 11,7-n Salpetersäure/0,1-m Hydrazin verwendet. Bei beiden Varianten konnte das Uran(IV) mit einem Gemisch aus 15% Schwefelsäure/5% Phosphorsäure von der Kolonne eluiert werden. Bei der ersten Variante konnte das Uran(IV) auch mit 11,7-n Salpetersäure/0,1-m Hydrazin eluiert werden, wenn es nach der Trennung in salpetersaurer Lösung vorliegen sollte. Die Stabilität der Kolonnen und des Uran(IV), der Einfluß der HDEHP-Konzentration in Xylol und der Salpetersäurekonzentration sowie das Verhalten einiger Ionen bei den Trennbedingungen werden besprochen.

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Separation of uranium(VI) by extraction chromatography from the solutions resulting from nuclear technology

Summary The extraction-chromatographic separation of uranium(VI) from nitric acid solutions is described. Columns were employed containing di-(2-ethylhexyl)-phosphoric acid (HDEHP) in xylene as stationary phase. If only uranium(IV) and uranium(VI) are present, it is sufficient to elute with nitric acid/0.1M hydrazine. From solutions of more complex composition, which in addition to uranium(IV) and uranium(VI) also contain longer-lived fission products (¹⁴⁴Ce,¹⁰⁶Ru,⁹⁵Nb and¹³⁷Cs), plutonium(III) and corrosion products of steel [Fe(III), Co(II), Ni(II) and Cr(III)], the uranium(IV) was separated by two varieties. In the first variant it was retained on the column by 5% HDEHP in xylene and all accompanying ions were removed with 2N nitric acid/0.1M hydrazine. In the second variant, in addition to the uranium(IV), the uranium(VI) also was captured in a separate fraction. 30% HDEHP was employed as stationary phase, while the elution agent was 11.7N nitric acid/0.1M hydrazine. In both variants, the uranium(IV) could be eluted from the column by a mixture of 15% sulfuric acid/5% phosphoric acid. In the first variant, the uranium(IV) could also be eluted by means of 11.7N nitric acid/0.1M hydrazine in case it was planned to have it present after the separation in nitric acid solution. The stability of the columns and of the uranium(IV) and the influence of the HDEHP concentration in xylene and the nitric acid concentration as well as the behavior of several ions under the separation conditions are discussed.

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Herrn o. Univ.-Prof. Dr.Hans Nowotny zum 60. Geburtstag gewidmet.     

The investigation of the solvent extraction of molybdenum from concentrated solution of sulphuric acid

The solvent extraction of molybdenum(VI) from sulphuric acid solutions with di-(2-ethylhexyl)-phosphoric acid (HDEHP) and monododecylphosphoric acid (HDDP) in n-heptane has been studied (a) as a function of the concentration of sulphuric acid, molybdenum and the extractant; (b) in the presence of copper and zinc in the aqueous phase and (c) in the presence of tri-n-butylphosphate (TBP) in the organic phase. The distribution of the sulphuric acid between aqueous and organic phase has also been studied.     

Extraction-spectrophotometric determination of tungsten as tungsten blue

Tri-n-butyl phosphate (TBP) is used to extract tungsten(IV) from 0.5 M hydrochloric acid containing molybdenum(VI) and other metals. Tungsten(VI) in the TBP solution is reduced by tin(II) chloride and n-butyl acetate is used for dilution. The tungsten blue formed in the TBP/n-butyl acetate medium (1:1) is measured at 615 nm. The apparent molar absorptivity is about 1000 1 mol^?1 cm^?1; calibration graphs are linear in the range 0.1–1.5 mg of tungsten.     

The application of novel hydrophobic ionic liquids to the extraction of uranium(VI) from nitric acid medium and a determination of the uranyl complexes formed

Novel ammonium based hydrophobic ionic liquids (ILs) have been synthesised and characterised, and their use in the liquid-liquid extraction of uranium(VI) from an aqueous nitric acid solution using tri-n-butyl phosphate (TBP), studied. On varying the nitric acid concentration, each IL was found to give markedly different results. Relatively hydrophilic ILs showed high uranium(VI) extractability at 0.01 M nitric acid solution which progressively decreased from 0.01 to 2 M HNO(3) and then increased again as the nitric acid concentration was increased to 6 M. An analysis of the mechanisms involved for one such IL, pointed to cationic-exchange being the predominant route at low nitric acid concentrations whilst at high nitric acid concentrations, anionic-exchange predominated. Strongly hydrophobic ILs showed low extractability for nitric acid concentrations below 0.1 M but increasing extractability from 0.1 M to 6 M nitric acid. The predominant mechanism in this case involved the partitioning of a neutral uranyl complex. The uranyl complexes were found to be UO(2)(2+)·(TBP)(3) for the cationic exchange mechanism, UO(2)(NO(3))(2)(TBP)(2) for the neutral mechanism and UO(2)(NO(3))(3)(-)·(TBP) for the anionic exchange mechanism.     

Extraction of Am(III) from different acid media by di-2-ethyl hexyl phosphoric acid containing phosphorous pentoxide

The extraction of Am(III) from nitric, hydrochloric, oxalic, phosphoric and hydrofluoric acids was studied using 0.4F di-2-ethyl hexyl phosphoric acid (HDEHP) containing 0.1M phosphorous pentoxide (P₂O₅) in dodecane/xylene. The extraction with pure 0.4F HDEHP was found to be negligible from all the media studied. However, the presence of a small amount of P₂O₅ in it increased the extraction substantially. The distribution ratios of Am(III) obtained for HDEHP - P₂O₅ mixture 3M nitric acid containing different concentrations of oxalic acid/phosphoric acid/hydrofluoric acid are in the order of 200-250. The same for 3M hydrochloric acid is very high (800). These distribution ratios are sufficiently high for the quantitative extraction of Am(III) from all the acid media studied. Different reagents such as ammonium oxalate, sodium oxalate, oxalic acid, hydrofluoric acid, sodium carbonate and potassium sulphate were explored for the back extraction of Am(III) from 0.4F HDEHP + 0.1M P₂O₅ in dodecane/xylene. Of these, 0.35M ammonium oxalate and 1M sodium carbonate were found to be most suitable. The back extraction of Am(III) was also attempted with water and 1M H₂SO₄, HNO₃, HClO₄ and HCl solutions after allowing the extracted organics to degrade on its own. It was found that more than 90% of Am could be back extracted with these acids. Using this method more than 90% of Am(III) was recovered from nitric acid solutions containing calcium and fluoride ions.     

Cerium isotope partition in HNO3/TBP or HDEHP extraction systems

The^142/140Ce unit separation factors (q) for cerium(III)-cerium(IV) exchange reaction in an extraction system containing Ce(IV) in tri-n-butyl phosphate (TBP) or di(2-ethylhexyl) phosphoric acid (HDEHP) and Ce(III) in nitric acid were determined. The value of q was found to be 1.00054±0.00012 (2) in 6M HNO₃/TBP and 1.00078±0.00028 in 6M HNO₃/HDEHP extraction systems. The dehydration and complex formation processes and their contribution to reduced partition function ratios (RPFR's) are discussed.     

Methyl isobutyl ketone extraction of iodide complexes from sulphuric acid-potassium iodide media and back-extraction into an aqueous phase

The methyl isobutyl ketone extraction of 15 elements (Cu, Ag, Zn, Cd, In, Tl, Ge, Sn, As, Sb, Bi, Se, Te, Mo and Pd) as iodide complexes from 0.1-5 M sulphuric acid/0.01-0.5M potassium iodide media has been studied. At the optimum potassium iodide concentrations, and a 1:2 v v ratio of organic to aqueous phase, Cu(II), Ag, Cd, In(III), Tl(III), Sb(III), Bi, Te(IV) and palladium(II) are completely extracted in a single step from 1-5M sulphuric acid. All these elements except palladium are also quantitatively extracted from 0.05-0.5M iodide/2M sulphuric acid. Zn, Sn(IV) and As(III) are completely extracted at high acid and iodide concentrations, and at the highest concentrations of acid and iodide investigated, Ge is partly extracted and Mo(VI) is slightly extracted. The extraction of Se(IV) is incomplete because of its reduction to the elemental state by iodide. The back-extraction of the elements has also been investigated and the forms in which they are extracted and potential analytical separations and interferences are discussed.     

Polarographic waves of tri-n-butyl phosphate and polarographic determination of uranium in the presence of tri-n-butyl phosphate

The results of a study on the polarographic behaviour of TBP and its influence on the determination of uranyl ions is presented. The half-wave potential of the adsorption wave of TBP depends on the concentration of TBP, type of supporting elec trolyte and its concentration. In the presence of TBP the polarographic wave of U(VI) ion is changed. Below 7·10^?5 M TBP the polarographic wave of U(VI) is not affected, between 7·10^?5 and 2·10^?4 M TBP the shape, height and half-wave potential of U(VI) waves are changed and above 2·10^?4 M, up to saturated solution of TBP, the waves of U(VI) do, not change further. The bes supporting electrolytes for the determination of U(VI) are KNO₃ or NaClO₄ in concentrations of 0.1 to 0.5 M, pH 1–2 and TBP concentrations from 3·10^?4 to 1.2·10^?3 M.     

A pulse radiolysis investigation of the reactions of tributyl phosphate with the radical products of aqueous nitric acid irradiation

Tributyl phosphate (TBP) is the most common organic compound used in liquid-liquid separations for the recovery of uranium, neptunium, and plutonium from acidic nuclear fuel dissolutions. The goal of these processes is to extract the actinides while leaving fission products in the acidic, aqueous phase. However, the radiolytic degradation of TBP has been shown to reduce separation factors of the actinides from fission products and to impede the back-extraction of the actinides during stripping. As most previous investigations of the radiation chemistry of TBP have focused on steady state radiolysis and stable product identification, with dibutylphosphoric acid (HDBP) invariably being the major product, here we have determined room temperature rate constants for the reactions of TBP and HDBP with the hydroxyl radical [(5.00 +/- 0.05) x 10(9), (4.40 +/- 0.13) x 10(9) M(-1) s(-1)], hydrogen atom [(1.8 +/-0.2) x 10(8), (1.1 +/- 0.1) x 10(8) M(-1) s(-1)], nitrate radical [(4.3 +/- 0.7) x 10(6), (2.9 +/- 0.2) x 10(6) M(-1) s(-1)], and nitrite radical (<2 x 10 (5), <2 x 10(5) M(-1) s(-1)), respectively. These data are used to discuss the mechanism of TBP radical-induced degradation.     

Extraction behavior of moybdenum and zirconium with diisodecylphosphoric acid from nitric acid solution

This study was performed mainly from the viewpoint of consumption of diisodecylphosphoric acid (DIDPA) by the extracted Mo and Zr to estimate extraction capacities. The number of DIDPA molecules consumed per one extracted Mo atom was four when the concentration of Mo in the aqueous phase was less than 10^–3M and it decreased with increasing Mo concentration. Two molecules of DIDPA were consumed per one extracted Zr atom when the Zr concentration was high. Dependencies of the distribution ratio of Mo on the concentrations of Mo, DIDPA and HNO₃ are also described.     

Extraction Kinetics of Uranium(VI) with di(2-ethylhexyl) Phosphoric Acid Using a Hollow Fiber Membrane Extractor

The kinetics of solvent extraction of U(VI) with di(2-ethylhexyl) phosphoric acid (HDEHP) using a microporous hydrophobic hollow fiber membrane extractor has been investigated. The effects of U(VI) and hydrogen ion concentrations in aqueous phase, HDEHP concentration in organic phase, flow velocities of aqueous and organic phase and temperature on extraction rate of U(VI) were examined. The experimental results suggest that the extraction rate of U(VI) is controlled by diffusion.     

Spectrophotometric measurement of uranium(VI)-tributylphosphate complex in supercritical carbon dioxide

UV-visible absorption spectra of uranium(VI)-tributylphosphate (U(VI)-TBP) complex dissolved in supercritical CO(2) at 40-60 degrees C and 100-250 kg cm(-2) were recorded. Wavelengths and molar extinction coefficients for the absorption peaks of U(VI)-TBP were determined and confirmed to be in good agreement with those of UO(2)(NO(3))(2)(TBP)(2) complex dissolved in organic solvents such as n-hexane. The absorbance at a given wavelength was proportional to the concentration of U(VI) species in supercritical CO(2), indicating a feasibility of in-situ determination of U(VI) concentration in CO(2) phase. A lower detection limit of U(VI)-TBP complex was estimated to be ca. 1x10(-3)M. The molar extinction coefficient of U(VI)-TBP in supercritical CO(2) decreased slightly with an increase of the density of CO(2) medium, suggesting that the solute-solvent interaction of U(VI)-TBP complex with CO(2) was affected by the density. On the basis of the spectra obtained, phase behavior and solubility of UO(2)(NO(3))(2)(TBP)(2)+H(NO(3))(TBP)+TBP in supercritical CO(2) were elucidated.     

Reduction kinetics of Pu(IV) and Np(VI) by N,N-dimethylhydrazine,and its potential application in nuclear fuel reprocessing

Reduction kinetics of Pu(IV) by N,N-dimethylhydrazine (NNDMH) were studied by spectrophotometry, and the reduction rate equation in 3M (mol/dm³) nitric acid was obtained. The reduction properties of NNDMH for U(VI), Np(VI), and Pu(IV) was studied in the mixture solution of trin-butylphosphate diluted to 30 vol.% by n-dodecane (30% TBP) and 3M nitric acid. It was confirmed that NNDMH selectively reduce Np(VI) to Np(V) without affecting the valences of U(VI) and Pu(IV) in a few minutes. Numerical simulation indicated that 99.9% of Np was separated from U and Pu applying NNDMH for a mixer-settler.