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The kinetics of U(VI) ion transport from an aqueous donor phase to an aqueous acceptor phase were investigated using a recently designed system, the multi-dropped liquid membrane system (MDLM). Equilibrium and kinetic studies were performed involving the extraction of U(VI) from an aqueous nitrate medium into tri-n-octyl phosphine oxide (TOPO). The influences of temperature, carrier, and donor phase concentrations were investigated. U (VI) was extracted from the donor phase to the acceptor in 45 min with an extraction efficiency of about 99.62% under optimum conditions. The interface reactions' kinetic parameters (k1, k2, C B max , t B max , J d max , J a max ) were estimated on the assumption of two successive, irreversible first-order reactions. This study investigated the conditions of transport by TOPO in the extraction of U(VI) ions in the MDLM system and obtained successful results. [ABSTRACT FROM AUTHOR]

[Display omitted] • TOPO/PAN capsules are facile synthesis and low cost; • U(VI) has fast kinetic adsorption rate (about 1 h) and large adsorption capacity(161.8 mg/g) on TOPO/PAN capsules in the acidic solution; • TOPO/PAN capsules exhibited good selectivity for U(VI) in the acidic solution and excellent reusability. The adsorption capacity and adsorption rate of most adsorbents for U (VI) are maximum in the pH value range of 5 ∼ 9. However, uranium-containing wastewater produced during uranium mining is usually highly acidic. Therefore, it is of great significance to prepare adsorbents suitable for the separation and enrichment of U(VI) ions from strongly acidic solutions. PAN capsules were synthesized by phase transformation method, and then impregnated TOPO in PAN capsules by impregnation method. TOPO/PAN has good morphology and higher adsorption capacity for U(VI) under acidic conditions. The effects of time, solid–liquid ratio, pH and ionic strength on TOPO/PAN adsorption of U(VI) were studied. The experimental results showed that the pseudo-second-order kinetic model and Langmuir model well described the kinetic and equilibrium data of adsorption process. The capsules have fast adsorption rate, good adsorption capacity and good ion selectivity in highly acidic solutions. After 5 cycles, the adsorption rate of TOPO/PAN is still above 96 % and the adsorption rate decreases by 1.2 %, which indicate that TOPO/PAN has good reusability. The research shows that TOPO/PAN has good practical application value. [ABSTRACT FROM AUTHOR]

Novel methods of separation and purification are envisaged for natural uranium, containing 0.7% of fissile 235U, a precious resource that fuels nuclear power plants. The present study demonstrates Solid phase extraction (SPE) of uranium as a sustainable alternative to conventional liquid-liquid extraction, leading to minimisation of organic inventory and enhancement of ease of operation concerning usage of viscous eutectic solvent. Overcoming the issue of the low solubility of organophosphorus extractant tri-octyl phosphine oxide (TOPO) in a hydrocarbon diluent, the aqueous insoluble, non-ionic eutectic solvent could be prepared with biodegradable menthol having TOPO: menthol mole ratio of 1:2 (MT2), 1:3 (MT3) and 1:4 (MT4). Eutectic solvents were sorbed on radio chemically stable Chromosorb W resin as solid support (MTC2, MTC3, MTC4), with loading of 45% for MTC2 and 40% for both MTC3 and MTC4, confirmed by weight difference and thermogravimetry. Batch sorption studies of U(VI) from nitric acid medium revealed attainment of equilibrium at 60 min., following a pseudo-second-order rate equation, Langmuir adsorption isotherm and a static capacity of 19 mg g−1. The U(VI) uptake was found to increase with the increase in acid molarity indicating solvating mechanism of extraction (K D = 1240 ± 4, 4 M HNO 3). Recyclability was established and stripping was effective with 0.5 M HNO 3. Column operation was also successfully demonstrated (breakthrough capacity = 18.9 mg g−1). The U(VI) uptake of >98% was indicated for nitric acid-digested crude yellow cake matrices viz. sodium diuranate (SDU), magnesium diuranate (MDU) and heat-treated uranium peroxide (HTUP). For higher matrix content, near complete uranium uptake and suppression of extraction of representative impurities (Fe, Mn, Ni, Ce) was revealed indicating facile uranium separation and purification from matrices relevant to the front end of the nuclear fuel cycle. • Bulk uranium SPE scheme, from matrices relevant to front-end, with TOPO and biodegradable menthol sorbed Chromosorb W • Reusable stationary phase simplifying process and minimising oragnic inventory • Batch and column operation reveal high U(VI) uptake (K D = 1240 ± 4) and capacity (19 mg g−1) • Chemisorption of uranyl, confirmed by UV–Vis spectrophotometry, IR and electrometry, onto TOPO in stationary phase • Demonstrated U(VI) uptake (> 98%) and suppression of extraction of representative impurities (Fe, Mn, Ni, Ce) [ABSTRACT FROM AUTHOR]

A methodology for separation and purification of 210Po from uranium, thorium and daughters has been studied. Solvent extraction coupled with liquid scintillation analysis using HDEHP (di-(2-ethylhexyl) phosphoric acid) and TOPO (trioctylphosphine oxide) in toluene as extractive scintillator was optimized. About 95% of 210Po was extracted in the organic phase of TOPO as an extracting agent from an aqueous solution in 1 M HCl, compared to 1.6% extraction by HDEHP. The methodology was validated with uranium ore tailing sample, IAEA-385 sediment and IAEA-447 Moss-soil reference materials for application to environmental samples. A minimum detectable activity of 118 mBq kg−1 was achieved. [ABSTRACT FROM AUTHOR]

In the method, soil was fused together with NaCO and NaO at 600 °C, uranium and thorium were leached out with HCl, HNO and HF, and HClO was used to eliminate the residual HF through evaporation. The leaching solution (2 M HNO) was passed through a Microthene-TOPO column to adsorb uranium and thorium. Thorium was first eluted with 2 M HCl and electrodeposited in 0.025 M HCO + 0.15 M HNO on a stainless steel disc. Uranium was eluted with a 0.025 M ammonium oxalate solution and also electrodeposited. Both thorium and uranium isotopes on the discs were measured separately by α-spectrometry. [ABSTRACT FROM AUTHOR]

In recent years, Supercritical Fluid Extraction (SFE) technique has been widely used for the extraction of metal ions. In the present study, extraction of uranium from nitric acid medium was investigated using supercritical carbon dioxide (Sc-CO2) containing various organophosphorous compounds such as trialkyl phosphates e.g. tri- iso-amyl phosphate (TiAP), tri- sec-butyl phosphate (TsBP) and tri- n-butyl phosphate (TBP), dialkylalkyl phosphonates, e.g. diamylamyl phosphonate (DAAP) and dibutyl butyl phosphonate (DBBP), dialkyl hydrogen phosphonates, e.g. dioctyl hydrogen phosphonate (DOHP), dioctylphosphineoxide (DOPO), trioctyl phosphine oxide (TOPO), n-octylphenyl N,N-diisobutyl carbamoylmethylphosphine oxide (CMPO) and di-2-ethyl-hexyl phosphoric acid (HDEHP). Some of these ligands have been investigated for the first time in the supercritical phase for the extraction of uranium. The extraction efficiency of uranium was studied with TiAP, DAAP and DBBP as a function of nitric acid concentration; the kinetics of the equilibration period (static extraction) and transportation of the metal complex (dynamic extraction) was investigated. The influence of pressure and temperature on the extraction behaviour of uranium with DAAP was studied from 4 N HNO3. The extraction efficiency of uranium from 4 N nitric acid medium was found to increase in the order of phosphates < phosphonates < HDEHP < TOPO < CMPO. In the case of phosphates and phosphonates, the maximum extraction of uranium was found to be from 4 N HNO3 medium. The acidic extractants, HDEHP and DOHP showed relatively higher extraction at lower acidities. The relative extraction of uranium and thorium from their mixture was also examined using Sc-CO2 containing phosphates, phosphonates and TOPO. The ligand, TsBP provided better fractionation between uranium and thorium compared to trialkyl phosphates, dialkyl alkyl phosphonates and TOPO. [ABSTRACT FROM AUTHOR]

This paper studied the recovery of uranium (VI) from 5.3 M phosphoric acid by bis(1,3-dibutoxypropan-2-yl) phosphoric acid (BiDiBOPP)/di- n -hexyl octyl metoxy phosphine oxide (di-n-HMOPO) and 5 analogs of BiDiBOPP mixed with tri- n -octylphosphine oxide (TOPO) diluted in Isane IP 185. First, this paper shows that the experimental and calculated distribution coefficients of uranium (VI) as a function of the concentration of BiDiBOPP and di- n -HMOPO match by using a thermodynamic model previously developed and validated on the bis(2-ethylhexyl) phosphoric acid (D2EHPA)-TOPO system. In this model the formation of complexes between the cationic extractant (HL) and the solvatant extractant (S) such as (HL) 2 , (HL) 2 S, (HL) 2 S 2 and (HL) 5 S and the recovery of uranium (VI) as UO 2 (HL) 2 L 2 S, UO 2 L 2 S and UO 2 (HL) 2 L 2 were taken into account where L refers to the deprotonated form of the cationic extractant HL. Secondly, the investigation of the extraction of uranium (VI) by the BiDiBOPP analogs mixed with TOPO in Isane IP 185 showed that the presence of oxygen atoms in the two aliphatic chains of BiDiBOPP and the increase of the hydrophobicity of these chains influence strongly the extraction properties. [ABSTRACT FROM AUTHOR]

Abstract: The speciation of uranium(VI) present in aqueous solutions of 0.73–7.08mol.L−1 phosphoric acid or extracted from these solutions in various organic phases was investigated by time-resolved laser-induced fluorescence spectroscopy (TRLFS). The organic phases consisted of bis-(2-ethyl-hexyl) phosphoric acid (D2EHPA), bis(1,3-dibutyloxypropan-2-yl) phosphoric acid (BiDiBOPP) and synergistic mixtures of tri-n-octylphosphine oxide (TOPO) or di-n-hexyl octyl methoxy phosphine oxide (di-n-HMOPO) with D2EHPA or BiDiBOPP in Isane IP 185 (an aliphatic diluent). The present paper indicates that uranium(VI) exists as a unique species in aqueous solutions of 0.78–7.08mol.L−1 H3PO4 likely as UO2(H3PO4)n(H2PO4)m 2-m where n+m=3, and that a predominant uranium(VI) species (more than 90%) is extracted by the D2EHPA/TOPO synergistic mixture. This species, whose formula is likely UO2(HL)2L2TOPO with HL=monomeric D2EHPA and L=deprotonated form of D2EHPA, is characterized by the fact that the TOPO molecule is located in the first solvation shell of uranium(VI) as also confirmed by DFT calculations. Furthermore, TRLF spectra of uranium(VI) in D2EHPA/di-n-HMOPO and BiDiBOPP/di-n-HMOPO are quite different from those obtained with the D2EHPA/TOPO mixture. Indeed, the vibronic peaks of uranium(VI) TRLF spectra have partially (D2EHPA/di-n-HMOPO) or completely (BiDiBOPP/di-n-HMOPO) disappeared, which could be due to the presence of oxygen atoms in the hydrophobic chains of BiDiBOPP and di-n-HMOPO. As in the case of the D2EHPA/TOPO mixture, the fluorescence lifetime of uranium(VI) in the BiDiBOPP/di-n-HMOPO mixture indicates that uranium(VI) is extracted by this mixture from 5.3mol.L−1 H3PO4 as a unique or at least a predominant species. [Copyright &y& Elsevier]

The extraction of thorium(IV) and uranium(VI) from nitric acid solutions has been studied using mixtures of bis(2,4,4-trimethylpentyl)phosphinic acid (Cyanex272 or HA), and synergistic extractants (S) such as tri-butylphosphate (TBP), tri-octylphosphine oxide (TOPO) or bis(2,4,4-trimethylpentyl)thiophosphinic acid (Cyanex301). The results showed that these metallic ions are extracted into kerosene as Th(OH) 2(NO 3)A·HA and UO 2(NO 3)A·HA with Cyanex272 alone. In the presence of neutral organophosphorus ligands TBP and TOPO, they are found to be extracted as Th(OH) 2(NO 3)A·HA·S and UO 2(NO 3)A·HA·S. On the other hand, Th(IV), U(VI) are extracted as Th(OH) 2(NO 3)A·HA·2S and UO 2(NO 3)A·HA·S in the presence of Cyanex301. The addition of neutral extractants such as TOPO and TBP to the extraction system enhanced the extraction efficiency of both elements while Cyanex301 as an acidic extractant has improved the selectivity between uranium and thorium. The effect of TOPO on the extraction was higher than other extractants. The equilibrium constants of above species have been estimated by non-linear regression method. The extraction amounts were determined and the results were compared with those of TBP. Also, it was found that the binding to the neutral ligands by the thorium–Cyanex272 complexes follows the neutral ligand basicity sequence. [ABSTRACT FROM AUTHOR]

The extraction of uranium (VI) from 5.3 mol.L−1phosphoric acid with a series of phosphoric, phosphinic, dithiophosphoric, or dithiophosphinic acid derivatives (0.5 mol.L−1) in mixture with 0.125 mol.L−1TOPO in Isane IP 185 has been investigated. In the frame of the present work, eight acidic phosphorus and thiophosphorus compounds have been synthesized: bis(1,3-diisobutoxypropan-2-yl) phosphoric acid, bis(1,3-bis-(butylthio)propan-2-yl) phosphoric acid, bis(5,8,12,15-tetraoxanonadecan-10-yl) phosphoric acid, bis(1-butoxyheptan-2-yl) phosphoric acid, bis(undecan-6-yl) phosphoric acid, bis(2-(1,3-dibutoxypropan-2-yloxy)ethyl) phosphoric acid, bis(3-butoxy-2-(butoxymethyl)-2-methylpropyl) phosphinic acid, bis(1,3-dibutoxypropan-2-yl) dithiophosphoric acid. The properties of these molecules in mixtures with TOPO have been compared with those of other extractants such as bis(2-ethylhexyl) phosphoric acid, bis(2-ethylhexyl) dithiophosphoric acid, bis(2-ethylhexyl) phosphinic acid, Cyanex® 272, and Cyanex® 301. The replacement of phosphoric acid-type extractant by their phosphinic homologues dramatically decreases the affinity for uranium (VI) whereas the replacement of the phosphoric and phosphinic acid-type extractants by their dithio homologues affects positively the distribution coefficient of uranium (VI). It also appears that the steric hindrance effect is responsible for a significant decrease of the distribution coefficient of uranium (VI).Supplemental materials are available for this article. Go to the publisher's online edition ofSeparation Science and Technologyto view the free supplemental file. [ABSTRACT FROM PUBLISHER]

Abstract: A thermodynamic model has been developed to describe the extraction of uranium (VI) from 5.3molL−1 phosphoric acid (a typical concentration encountered in wet phosphoric acid) by mixtures of bis-(2-ethylhexyl)-phosphoric acid (D2EHPA, also denoted hereafter HL) and tri-n-octylphosphine oxide (TOPO). A good agreement between experimental and calculated distribution coefficients of uranium (VI) was obtained by taking into account the following species in the organic phase: (HL)2TOPO, (HL)5TOPO, (HL)2(TOPO)2, UO2(HL2)2, UO2(HL2)2TOPO, and UO2L2TOPO where L is the deprotonated form of D2EHPA (HL). The speciation of uranyl, TOPO and D2EHPA in the organic phase was derived from this model as a function of the concentrations of the latter species. [Copyright &y& Elsevier]

A method to simultaneously recover yttrium and uranium from phosphoric acid using DNPPA + TOPO and D2EHPA + TBP solvent systems has been developed. The solvent mixture DNPPA + TOPO is employed for merchant grade phosphoric acid, while the D2EHPA + TBP solvent system is employed for wet process phosphoric acid to recover uranium and yttrium. In the method, four steps are involved for the yttrium recovery: (1) yttrium is co-extracted with uranium using the two organic systems; (2) yttrium is selectively stripped from the loaded organic solutions; (3) yttrium is recovered from the strip liquor by double sulphate salt precipitation; (4) yttrium double sulphate salt is dissolved and precipitated with oxalic acid to generate pure yttrium product. Selective stripping of yttrium from the loaded organic solutions with various strip solutions was tested. It was found that 10% (w/v) Na2SO4 + 30% H2SO4 and H2SO4 (30 to 40%) are the most preferable conditions with more than 95% of yttrium recovered and less than 0.2% of uranium lost in the yttrium strip liquor. From the resultant strip liquor, more than 98% of yttrium was precipitated in the form of sodium yttrium double sulphate salt under the optimized conditions of 10% (w/v) Na2SO4, 60 ± 1°C and aging time of 45 min. Pure yttrium oxide with more than 99% was obtained after dissolution of the resultant double sulphate salt, precipitation with oxalic acid and calcination at a high temperature. Sodium contained in the yttrium oxide product was removed by washing steps using distilled water and it could be completely removed under the conditions of liquid to solid ratio of 50, 80 ± 5°C and washing for 30 min. A conceptual process flowsheet has been proposed to recover yttrium as a by-product of uranium from phosphoric acid. [ABSTRACT FROM AUTHOR]

The extraction of U(VI) from sulphate medium with 2-ethylhexyl phosphonic acid-mono-2-ethylhexyl ester (PC88A, HA in dimeric form) in n-dodecane has been investigated under varying concentrations of sulphuric acid and uranium. Slope analysis of uranium (VI) distribution data as a function of PC88A concentration suggests the formation of monomeric species, viz. UO(HA). This observation was further supported by the mathematical expression obtained during non-linear least square regression analysis of U(VI) distribution data correlating the percentage extraction (% E) and the acidity ( H). A mathematical model correlating the experimental distribution ratio values of U(VI) ( D) with initial acidity ( H) and initial uranium concentrations ( C) was developed: $$ D_{\text{U}} = 12.98( \pm 0.90)/\left\{ {C_{\text{i}}^{ - 0.75( \pm 0.05)} \times \left[ {H_{\text{i}} } \right]^{2} } \right\} $$. This expression can be used to predict the concentration of uranium in organic as well as in aqueous phase at any C and H. The extraction data were used to calculate the conditional extraction constant ( K) values at different acidities (2-7 M H), uranium (0.02-0.1 M) and PC88A (0.2-0.6 M) concentrations. These studies were also extended for the extraction of U(VI) using synergistic mixtures of PC88A and TOPO from sulphate medium. [ABSTRACT FROM AUTHOR]

The Th content in commercially available NdO samples with the main substance content of 99.0-99.998% was found to be 2-8, and that of U, 3-230 ppb. Therefore, to obtain Nd meeting the requirements of the experiment on studying neutrinoless double β-decay, it should be purified to reduce the content of Th and U impurities by a factor of 10-10. To this end, the extraction of Nd, Th, and U from hydrochloric acid media with solutions of trioctylphosphine oxide (TOPO) in toluene was studied. The distribution ratios of Th increase with a decrease in the HCl concentration in the initial aqueous solution. With an increase in the Cl concentration in the aqueous phase, the U distribution ratios decrease, probably because of a decrease in the concentration of the free extractant due to the extraction of Nd and HCl. On the contrary, the distribution ratios of Th increase with an increase in the Cl concentration in the aqueous phase, with the slope of the straight line in the coordinates log D-log[Cl] close to 7, which may be due to coextraction of Th with Nd in the form of the complex ThNdCl. The enthalpies of formation of the extractable complexes of Th and U were determined from the temperature dependence of the extraction of Nd, Th, and U chlorides with a 0.1 M solution of TOPO in toluene. The optimal extraction system was chosen for Nd purification to remove traces of Th and U: organic phase, 0.1 M solution of TOPO in toluene; aqueous phase, 2.4 M NdCl + 0.1 M HCl. From the initial aqueous solution contaning 574 ppt Th and 2837 ppt U, by single extraction with an equal volume of 0.1 M TOPO in toluene, an aqueous solution containing <10 ppt Th and 31 ppt U (detection limit 10 ppt) was obtained. By semicountercurrent extraction, from the initial aqueous NdCl3 solution containing 200 ppb Th, the raffinate containing <10 ppt Th was obtained in one extraction step. The results obtained confirm the possibility of exhaustive removal of Th and U impurities (to the level of ≤1 ppt) from Nd by extraction with TOPO solutions from chloride solutions. [ABSTRACT FROM AUTHOR]

Abstract: A cellulose triacetate (CTA) membrane containing trioctylphosphine oxyde (TOPO) as carrier and 2-nitrophenyloctyl ether (NPOE) as a plasticizer was prepared. The membrane CTA+NPOE+TOPO was characterised using chemical techniques as well as Fourier Transform InfraRed (FTIR) spectroscopy, X-ray diffraction and Scanning Electron Microscopy (SEM). The CTA membrane is characterised by well-defined pores; these pores are completely filled with the NPOE and carrier. Surfaces of membranes with TOPO are smooth. The systems constituted by the mixture of CTA+NPOE, CTA+NPOE+TOPO do not give any diffraction. This can be due to the absence of crystallization within the membrane. On the other hand, this result should be attributable to the amorphous state of the structure, which permits us to eliminate the mechanism of transfer of the ions by electron jump. A comparative study of transport across a polymer inclusion membrane (PIM) and a supported liquid membrane (SLM) containing the same carrier in chloroform has shown that uranium or molybdenum transport efficiency was increased using PIM instead of SLM. PIM showed higher stability than SLM, the flux of transport remain constant in the former case after 2weeks. [Copyright &y& Elsevier]

Abstract: Supercritical fluid extraction (SFE) of uranium and thorium from solid matrices was carried out employing CO2. Direct dissolution and extraction of oxides of uranium viz. UO2 and U3O8 was performed. UO2 and U3O8 powders (0.02–0.05 g) along with 2 ml of TBP–HNO3 complex were taken in extraction vessel and CO2 was fed until 150 atm. pressure and 60°C temperature were achievable. After 20 min uranium extraction was performed by continuously flowing supercritical fluid mixture of CO2 and 10% TBP for 45 min. Uranium extraction efficiency for U3O8 was 97.05 ± 3.73% and for UO2 was 98.07 ± 4.76%. For SFE of thorium from tissue paper matrix, TBP and TOPO (0.2 M in CCl4) were investigated as complexing agents. In online complexation mode, mixture of CO2 and 10% complexing agent was fed to the extraction vessel. The vessel was maintained at pressure of 200 atm. and temperature of 60°C for 20 min followed by 20 min of extraction. TOPO was found to be more effective than TBP as extraction efficiencies with TBP and TOPO were 52.51 ± 7.54% and 65.65 ± 7.78% respectively. The efficiency was found to improve with a combination of 1: 1 volume ratio of TBP and TOPO (0.2 M in CCl4). No further improvement was observed with TOPO plus 10% methanol. In in-situ mode higher efficiency i.e. 89.83 ± 7.04% was observed with employing TOPO as a complexing agent. Uranium and thorium were determined spectrophotometrically employing arsenazo III metal indicator for color development. [Copyright &y& Elsevier]

Abstract: Present studies deals with the application of supported liquid membrane (SLM) technique for the separation of uranium (VI) from phosphoric acid medium. Tri-n-octyl phosphine oxide (TOPO)/n-dodecane is used as a carrier and ammonium carbonate as a receiving phase for the separation of uranium (VI) from the phosphoric acid medium. Throughout the study PTFE membranes are used as a support. The studies involve the investigation of process controlling parameters like feed acidity of phosphoric acid, carrier concentration and stripping agents. The effect of nitric acid and sodium nitrate in feed is also studied. It is found that there is negligible transport of uranium (VI) from pure phosphoric acid medium but it increases to very significant amount if 2 M nitric acid is added to feed phase. More than 90% uranium (VI) is recovered in 360 min using 0.5 M TOPO/n-dodecane as carrier and 1.89 M ammonium carbonate as stripping phase from the mixture of 0.001 M H3PO4 and 2 M of HNO3 as a feed. The flux and permeability coefficient are found to be 9.21×10−6 mol/m2 s and 18.26×10−5 m/s, respectively. Lower concentration of phosphoric acid with 2 M HNO3 and higher concentration of carrier is found to be the most suitable condition for maximum transport of uranium (VI) from its low-level sources like commercial phosphoric acid. [Copyright &y& Elsevier]

An extensive study on separation and recovery of uranium (VI) from dilute aqueous solutions using a liquid emulsion membrane (LEM) technique is presented. The study has highlighted the importance of emulsion stability for maximizing uranium recovery. The emulsion constitutes tri-n-octylphosphine oxide (TOPO) as a carrier, paraffin as organic diluent, an emulsifying agent, and stripping phase. The residence time required for adequate pertraction of uranium has been evaluated. The important variables affecting the LEM permeation process such as the concentrations of surfactant, extractant, internal strip phase, and effect of speed of agitation, aqueous feed phase pH, and the presence of iron were systematically investigated. Using suitable values, an attempt was made to recover uranium from a synthetic process plant stream. It was found that strip phase sodium carbonate concentration of 0.5 M gives maximum recovery of uranium. The feed phase pH has been found to be critical for uranium recovery by this technique. [Copyright &y& Elsevier]