Linear alkylbenzene (LAB) as diluent for extractants. Extraction of rare-earth elements with solutions of neutral organophosphorus compounds in LAB

Extraction of REE with solutions of neutral organophosphorus compounds (TBP, TIAP, DIOMP) in a new diluent, linear alkylbenzene (LAB), was studied. LAB exhibits significant advantages over known diluents: high flash point (+147°C), nontoxicity, absence of odor, low cost, availability, and good compatibility with polymeric structural materials. LAB is well compatible with TBP, TIAP, and DIOMP. Extraction of HNO₃ and REE nitrates is not accompanied by precipitation of extractable complexes or by formation of a second organic phase in a wide concentration range, up to saturation of the extractant. The major extractable complex in extraction of REE nitrates is Ln(NO₃)₃·3NOPC, where NOPC = TBP, TIAP. The main parameters of extraction systems (distribution ratios, separation factors) with LAB are similar to those of the related systems with paraffin hydrocarbons as diluents. Experiments on group separation of REEs on a 56-step extraction installation gave results agreeing with the calculation data.     

Extraction of zirconium with tributyl phosphate from nitric acid solutions

The extraction of zirconium with tributyl phosphate (TBP) in organic diluent was studied. The dependence of the distribution ratio of Zr on the TBP concentration in the organic phase and also the IR spectra of Zr-TBP extracts obtained at different concentrations of Zr and HNO₃ in the aqueous phase show that at least two kinds of extractable zirconium nitrate solvates with TBP are formed in extraction with 30% TBP. The solvate formed at HNO₃ concentration not exceeding 3 M contains water molecules. The extract-able species formed at higher nitric acid concentration in the aqueous phase is anhydrous zirconium nitrate disolvate with TBP.     

Mathematical Simulation of Steady-State Concentration Profiles in Extraction Cascades for Reprocessing NPP Spent Fuel Using TBP-Compatible Processes (SUPERPUREX)

A mathematical model is proposed for calculating distribution coefficients of NPP spent fuel components in extraction systems with 30% TBP in a hydrocarbon diluent and dibutylphosphoric acid zirconium salt in 30% TBP. The model is based on the semiempirical extraction equations. A computer code has been developed for simulation of the steady-state concentration profiles throughout the extraction cascade. Comparison of the predicted and experimental data showed that the code is well applicable to simulation and optimization of the SUPERPUREX process.     

Synergistic extraction of REE and TPE from nitric acid solutions with chlorinated cobalt dicarbollide-dibutyl hydrogen phosphate mixture in a polar diluent

The extraction of Ce(III), Am(III), and Eu(III) from nitric acid solutions with chlorinated cobalt dicarbollide (CCD), dibutyl hydrogen phosphate (HDBP), and their mixtures in a polar diluent, m-nitrobenzo-trifluoride, was studied. The extraction with CCD-HDBP mixture is characterized by considerable synergistic effect. Its maximal value is close to 40 at HDBP to CCD molar ratio of 5–8 for all the metals under consideration. We believe that this synergistic effect is caused by formation of a complex acid from HDBP and CCD. This complex acid is more hydrophobic and more acidic than the initial reagents. In extraction of the metals from strongly acidic solutions, the HDHP to CCD ratio corresponding to optimal extraction decreases. This effect can be attributed to displacement of HDBP molecules from the extractable complex with HNO₃ molecules.     

Regeneration of Spent TBP-Diluent Solvent by Steam Distillation

Regeneration of irradiated and actual spent solvent (30% TBP in a hydrocarbon diluent) by overheated steam distillation was studied in batch experiments. The hydrodynamic and extraction-backwash parameters of thus regenerated solvent are practically the same as those of the fresh solvent. The bottoms comprise 3-7% of the initial volume and consist essentially of TBP. Large-scale rig trials of the single- and two-step continuous processes of solvent distillation are performed. Single-step distillation with overheated steam in a vacuum or with saturated water vapor at atmospheric pressure provides transfer into the distillate of the whole amount of the solvent, permitting the use of any diluent. The two-step process allows separation of the solvent into the TBP and diluent fractions and refining of each of them in the case when the diluent boiling point is below that of TBP by 50-70°.     

Extraction of REE(III), U(VI), and Th(IV) from Nitric Acid Solutions with Carbamoylmethylphosphine Oxides in the Presence of Dinonylnaphthalenesulfonic Acid

The extraction of REE(III), U(VI), and Th(IV) from nitric acid solutions with solutions of carbamoylmethylphosphine oxides (CMPOs) considerably increases in the presence of dinonylnaphthalenesulfonic acid. The stoichiometry of the extractable complexes was determined, and the influence of the aqueous phase composition, kind of organic diluent, and CMPO structure on the efficiency of the extraction of the metal ions was analyzed.     

Radiation-Chemical Behavior of TBP in Hydrocarbon and Chlorohydrocarbon Diluents under Conditions of Reprocessing of Spent Fuel from Nuclear Power Plants

Experiments were performed for comparative assessment of the effect of ionizing radiation on the service characteristics of 30% TBP solutions in various diluents: hexachlorobutadiene (HCBD), mixtures of n-paraffins (RED diluent), and fraction of naphthenic hydrocarbons (RZh diluent). The following main parameters were chosen for comparative assessment of the quality of irradiated extractant solutions: composition and behavior of diluent radiolysis products, effect of diluents on the TBP radiolysis, and aggregative stability of emulsions in the main operations of the extraction cycle. The service life of the extraction mixtures was estimated from variation of the above parameters with the irradiation dose. Principles for choosing solvents with increased service life under irradiation were substantiated.     

Development and trials of a process for extraction recovery of <Superscript>99</Superscript>Mo for medical purposes from dissolved irradiated uranium targets

A process was developed for extraction recovery of ⁹⁹Mo from irradiated enriched uranium target. Dissolution of the uranium–aluminum composite in nitric acid in the presence of fluoride ions with the addition of mercury ions, which are subsequently separated by precipitation in the form of iodide, was suggested. Conditions were determined for joint recovery of uranium and molybdenum into the organic phase with 10–15% solutions of HDEHP in a paraffin diluent in the presence of equimolar amounts of TBP, and also for selective backwashing of Mo into a strongly acidic H₂O₂ solution with the backwash reflux. The efficiency of using a mixture of DTPA with methylamine carbonate for uranium backwashing and solvent regeneration was demonstrated. The recovery and separation process was successfully tested on simulated and real solutions in 20- and 19-step cascades of centrifugal contactors with the feed adjuster without Mo backwash reflux and with its reflux, respectively.     

Effect of γ-irradiation on the thermal decomposition of nitric acid saturated solutions of TBP in С13 diluent

The dynamics of gas evolution in the course of thermal oxidation of 30% solutions of tri-n-butyl phosphate (TBP) in C13 diluent, equilibrated with 12.9 M HNO₃, was studied in open vessels in the temperature interval from 70 to 150°С. The total volumes of the released gases were measured, and the effect of the preliminary γ-irradiation of the TBP–С13–HNO₃ system on the thermolysis of nitric acid and accumulation of liquid products of TBP decomposition was studied. The boundary temperature parameters for the development of the oxidation process in the autocatalytic mode were estimated. On heating of the single-phase systems in open vessels, the conditions for the development of the autocatalytic oxidation are not created.     

Kinetics of oxidation of 30% TBP solutions in С13 diluent with nitric acid: Effect of temperature and γ-irradiation

The behavior of the two-phase system consisting of a 30% solution of tri-n-butyl phosphate (TBP) in a paraffin diluent (C13) and a 12 M aqueous HNO₃ solution was studied in the temperature interval from 70 to 110°С. The parameters of thermolysis of TBP solutions in C13 in the reaction with HNO₃ in open vessels were determined with the aim of evaluating the explosion hazard of the system in the course of extraction reprocessing of high-level radioactive materials. Solutions of TBP in C13 in the two-phase systems are characterized in the examined temperature interval by more intense gas evolution compared to that from the singlephase systems.     

Coextraction and successive selective stripping of cerium(IV) and thorium from monazite leach solutions with tributyl phosphate (TBP)

Solvent extraction of Ce(IV) and Th(IV) from 8 M HNO₃ with TBP in kerosene was studied. The dependence of the extraction on the TBP concentration, kind of diluent, O/A phase ratio, and contact time was examined. The extraction efficiency reaches 99.3 and 97.7% for Ce and Th, respectively, at 5% TBP in kerosene, 1/1 O/A phase ratio, and 5 min contact time. Successive selective stripping of Ce(III) and Th(IV) from the loaded organic phase was reached at 1.1 M H₂O₂ concentration, 10 min contact time, 3/1 O/A phase ratio, and room temperature (25 ± 2°C). After stripping of cerium, the remaining organic was contacted with H₂O for thorium stripping at 5 min contact time, 2/1 O/A phase ratio, and room temperature (25 ± 2°C).     

Extraction of REE(III), U(VI), and Th(IV) from Nitric Acid Solutions with Carbamoylmethylphosphine Oxides in the Presence of Bis[(trifluoromethyl)sulfonyl]imide Ions

Extraction of microamounts of REE(III), U(VI), and Th(IV) with solutions of carbamoylmethylphosphine oxides (CMPOs) in organic diluents from aqueous HNO₃ solutions containing lithium bis[(trifluoromethyl) sulfonyl]imide (LiTf₂N) was studied. The efficiency of the REE(III), U(VI), and Th(IV) extraction from nitric acid solutions with CMPO solutions considerably increases in the presence of Tf₂N^– ions in the aqueous phase. The stoichiometry of the extractable complexes was determined, and the influence of the structure of the CMPO molecule, kind of organic diluent, and aqueous phase composition on the efficiency of the U(VI), Th(IV), and REE(III) extraction into the organic phase was considered.     

Effect of Irradiation of the Extraction Mixture with 30% TBP in ISOPAR-M on the Lower Temperature Limit of Flame Propagation

Radiochemistry - Irradiation with accelerated electrons of an extraction mixture of 30% TBP in Isopar-M isoparaffin diluent on the lower temperature limit of flame propagation (Тl) has been...     

Extraction Properties of Bis(diphenylphosphinylethyl)phosphinic Acid in Nitric Acid Solutions

Extraction of microamounts of U(VI), Th(IV), Sc(III), and Ln(III) from HNO₃ solutions with solutions of bis(diphenylphosphinylethyl)phosphinic acid in dichloroethane was studied. The stoichiometry of the extractable complexes was determined, and the effect of the inorganic anion and organic diluent on the extraction of rare-earth elements was examined. An increase in the number of phosphoryl groups in the extractant molecule and replacement of ethylene bridges between the phosphorus atoms by methylene bridges enhance the extraction of metal ions from nitric acid solutions.__________Translated from Radiokhimiya, Vol. 47, No. 3, 2005, pp. 252–256.Original Russian Text Copyright © 2005 by Turanov, Karandashev, Ragulin.     

A new approach to mathematical description of the extraction of HNO3, U(VI), and other hexavalent actinides with tributyl phosphate in a mixture with paraffins

The isotherm of uranyl nitrate extraction with TBP in diluent without salting-out agents with the formation of the disolvate is described by a chemical equation with the concentration constant of 10 without correction coefficients in a wide range of component concentrations. The concentration of “free” TBP in the dependence of the extraction of U(VI) microamounts on the acid concentration was calculated using this value, and it was shown that the formal stoichiometric ratio TBP: HNO₃ in the extract is 0.75. To describe this effect, a set of reactions was suggested, taking into account the role of extracted water, and the corresponding concentration equilibrium constants were calculated without corrections. The values obtained differ significantly from those suggested previously. The constants obtained adequately describe the joint extraction of U(VI) and HNO₃ at the acid concentration of 0.3–8 M and extract loading with U(VI) of up to 85% of its capacity. At low extract loadings and acid concentration lower than 1 M, weak hydrolysis of uranyl ion and extraction of U(VI) hydrate solvate were taken into account. For the extraction of Np(VI) and Pu(VI) with TBP in diluent, the extraction constants that do not vary with the U(VI) and HNO₃ concentrations were calculated taking into account the formation of the Np(VI) and Pu(VI) hydrate solvates.     

Extraction of Lanthanide(III) Nitrates from Aqueous Nitrate Solutions with Tri-<Emphasis Type="Italic">n</Emphasis>-butyl Phosphate in Hexane and Tetradecane (Two- and Three-Phase Systems)

Extraction of lanthanide(III) nitrates [La-Sm(III)] with 1.83 mol dm⁻³ tri-n-butyl phosphate (TBP) in hexane and tetradecane was studied at 298.15 K. The extraction with TBP in hexane proceeds in two-phase systems, and with TBP in tetradecane, in two- and three-phase systems. Extraction in multiphase systems was mathematically treated.__________Translated from Radiokhimiya, Vol. 47, No. 4, 2005, pp. 351–354.Original Russian Text Copyright © 2005 by Pyartman, Keskinov, Kudrova.     

Extractive Properties of P,P'-Di(2-ethylhexyl) Dihydrogen 1-Hydroxyethane-1,1-diphosphonate in Nitric Acid Solutions

Extraction of microamounts of U(VI), Th(IV), Am(III), and rare-earth elements from aqueous HNO₃ solutions with solutions of P,P'-di(2-ethylhexyl) dihydrogen 1-hydroxyethane-1,1-diphosphonate in organic diluents was studied. The stoichiometries of the extractable complexes were determined, and the effect of organic diluent on the extraction was considered. P,P'-Di(2-ethylhexyl) dihydrogen 1-hydroxyethane-1,1-diphosphonate extracts Am(III) more efficiently than does P,P'-di(2-ethylhexyl) dihydrogen methanediphosphonate.     

Separation of beryllium (II) and aluminium (III) by solvent extraction using Bis-2 ethylhexyl phosphoric acid [HDEHP]

A simple and rapid method for the extraction is described for the separation of beryllium (II) and aluminium (111) from aqueous sulphate solution with Bis-2 ethylhexyl phosphoric acid (HDEHP) in toluene. A systematic study of the solvent extraction of chemically similar elements, beryllium (II) and aluminium (III) was carried out separately and it has been observed that under certain specific conditions beryllium (II) and aluminium (III) can be separated in a short period from their mixture using HDEHP as an extractant.     

Extraction of U(VI), Th(IV), and REE(III) from Nitric Acid Solutions with 2,6-Bis(diphenylphosphorylmethyl)pyridine <Emphasis Type="Italic">N</Emphasis>-Oxide

The extraction of microamounts of U(VI), Th(IV), and REE(III) from HNO₃ solutions in the form of complexes with 2,6-bis(diphenylphosphorylmethyl)pyridine N-oxide (I) was studied in relation to the kind of organic diluent and to the HNO₃ concentration in the equilibrium aqueous phase. The stoichiometry of the extractable complexes was determined. With respect to the ability to extract Th(IV) and REE(III), compound I considerably surpasses tetraphenylmethylenediphosphine dioxide and tetraalkyl-substituted analogs of I.     

Extraction of U(VI), Th(IV), Pu(IV), and Am(III) from nitric acid solutions with polyfunctional organophosphorus acids

Extraction of microamounts of U(VI), Th(IV), Pu(IV), and Am(III) nitrates from aqueous HNO₃ solutions with solutions of (diphenylphosphinylmethyl)phenylphosphinic, (di-p-tolylphosphinylmethyl)phenylphosphinic, and (dioctylphosphinylmethyl)phosphinic acids and of butyl hydrogen (diphenylphosphinylmethyl)phosphonate in organic diluents was studied. The metal: extractant stoichiometric ratio in the extractable complexes was determined, and the diluent effect on the extraction efficiency was examined. The possibility of using a macroporous polymeric sorbent impregnated with (dioctylphosphinylmethyl)phenylphosphinic acid for concentrating metal ions from HNO₃ solutions was demonstrated.