DISTRIBUTION BEHAVIOUR OF U(VI), Th(IV) AND Pa(V) FROM NITRIC ACID MEDIUM USING LINEAR AND BRANCHED CHAIN EXTRACTANTS

ABSTRACT

The extraction behaviour of 1M solutions of tri-2-ethylhexyl phosphate (TEHP), di-2-ethyl hexyl isobutyramide (D2EHIBA), tri-n-butyl phosphate (TBP) and di-n-hexyl hexanamide (DHHA) in n-dodecane towards U(VI), Th(IV) and Pa(V) in the presence of 220 g/L of Th from nitric acid medium has been studied. The limiting organic concentrations (LOC) of thorium (g/L) for 1 M TBP and 1 M DHHA are evaluated as 31, 20 ( at 1 M HNO₃) and 25,13 (at 4 M HNO₃) respectively. The distribution ratio (D) values of U(VI), Th(IV) and Pa(V) in the presence of thorium (220 g/L) at. 1 M HNO₃ suggest that branching in the alky group of amides suppresses the extraction considerably. In view of the selective extraction of U over Th by 5 % TBP in THOREX process at 4 M HNO₃, distribution behaviour is also studied employing a lower concenfration (0·18 M) of extractant for comparison purpose, Separation factor (S. F.) values for U(VI) over Th(IV) under different experimental conditions consistently varied in the order: D2EHIBA > DHHA > TEHP > TBP. The quantitative extraction of ²³³U from a synthetic mixture containing ²³³U (10^?5 M). ²³³Pa (10^?11 M) and thorium (220 g/L) at 1 M HNO₃ using 1 M solution of D2EHIBA in n-dodecane is achieved in three stages, Stripping and reusability studies of D2EHIBA have also been carried out.     

Adsorption of Eu(III), Th(IV), and U(VI) by mesoporous solid materials bearing sulfonic acid and sulfamic acid functionalities

ABSTRACT

SBA-15 mesoporous materials modified by sulfonic acid and sulfamic acid functionalities, abbreviated as SBA-15/SO₃H and SBA-15/NHSO₃H, were synthesized and applied for the removal–separation of Eu(III), Th(IV), and U(VI). SBA-15/NHSO₃H showed an excellent selectivity toward U(VI), while SBA-15/SO₃H was more efficient adsorbent for Eu(III) and Th(IV). It was found that in the presence of KNO₃ (1 mol L^?1), the separation of Eu(III)/Th(IV) from their mixtures is possible. The results of the sorption behavior indicated a high adsorption capacity toward U(VI) and Th(IV) ions (140.5 and 106.7 mg g^?1, respectively) and ultrafast kinetics (15 min) in Eu(III) adsorption.     

Effect of an electric field on the transport of Th(IV) in the presence of Eu(III) and U(VI) through supported liquid membrane containing di‐2‐ethylhexylphosphoric acid

This paper investigates the transport of Th(IV) ions in nitric acid media through a supported liquid membrane (SLM) impregnated with di‐2‐ethylhexylphosphoric acid (HDEHP) in kerosene using an electric field. The transport was carried out in a three compartment cell fitted with microporous cellulose nitrate (SLM) and cation exchange membrane (Nafion). The effect of different parameters including nitric acid concentration in the feed solution, HDEHP concentration in the membrane, and HCl concentration were studied. The optimal conditions for Th(IV) transport were 0.1 mol dm^?3 HDEHP, 10^?3 mol dm^?3 HNO₃ in the feed solution, 1 mol dm^?3 HCl in compartment 2 and 1 mol dm^?3 HCl in compartment 3 at 25 °C. Under the optimal conditions of Th(IV) transport the recovery factor after 90 min was 0.25 without applying an electrostatic field, compared with 0.9 when the electric field was applied. The effect of electric current on the flux of Th(IV) through the membrane was also studied. The flux increased as the current density increased from 10 to 30 mA cm^?2 to reach a maximum value at 30 mA cm^?2 (8 × 10^?9 g eq cm^?2 s^?1). The transport percentages of 0.3 g dm^?3 Th(IV) in the presence of 0.1 g dm^?3 Eu(III) and 1 g dm^?3 U(VI) were 66, 84 and 15%, respectively. The determined selectivities of U(VI)–Th(IV) and Th(IV)–Eu(III) were 0.12 and 0.3, respectively, after 90 min. Therefore, the order of selectivity of this system is Eu(III) > Th(IV) > U(VI). © 2001 Society of Chemical Industry     

Separation of Electrochemically Generated Ce(IV) from Rare Earths(III) in Nitric Acid Media by TBP Impregnated Resin

Abstract

Electro‐oxidation of Ce(III) to Ce(IV) in nitric acid media at different anode materials with high oxygen evolution overpotential was carried out. Ce(IV) nitrato complexes were adsorbed on a novel resin, based on porous silica beads with immobilized polystyrene/DVB copolymer, that was impregnated with tri‐n‐butyl phosphate (TBP). Under the studied conditions, Ce(IV) sorption increased with increasing nitric acid concentration (0.5–6 mol · dm^?3). Oxidation of sorbent by adsorbed Ce(IV) species resulting in Ce(III) release to the solution was observed and thoroughly evaluated. In spite of problems with TBP leakage (12%), column separation of pure Ce(IV) from Y(III) and La(III) was achieved in 6 mol · dm^?3 HNO₃ at 288 K. Ce(IV) breakthrough capacity was 0.48 mol · kg^?1‐TBP. Column regeneration with 0.1 mol · dm^?3 nitric acid yielded Ce solution with purity higher than 99.99 wt.% with respect to La and Y impurities.     

Thorium Ions Transport across Tri-n-butyl Phosphate—Benzene Based Supported Liquid Membranes

Abstract

Transport of Th(IV) ions across tri-n-butyl phosphate (TBP) benzene based liquid membranes supported in microporous hydrophobic polypropylene film (MHPF) has been studied. Various parameters such as variation of nitric acid concentration in the feed, TBP concentration in the membrane, and temperature on the given metal ions transport have been investigated. The effects of nitric acid and TBP concentrations on the distribution coefficient were also studied, and the data obtained were used to determine the Th ions—TBP complex diffusion coefficient in the membrane. Permeability coefficients of Th(IV) ions were also determined as a function of the TBP and nitric acid concentrations. The optimal conditions for the transport of Th(IV) ions across the membrane are 6 mol·dm^?3 HNO₃ concentration, 2.188 mol·dm^?3 TBP concentration, and 25°C. The stoichiometry of the chemical species involved in chemical reaction during the transport of Th(IV) ions has also been studied.     

Selective Extraction and Separation of Ce (IV) and Th (IV) from RE(III) in Sulfate Medium using Di(2-ethylhexyl)-N-heptylaminomethylphosphonate

The extraction and separation of Ce(IV) and Th(IV) from trivalent rare earths (RE, including scandium) in sulfate medium using di(2-ethylhexyl)-N-heptylaminomethylphosphonate (DEHAMP, L) were studied. The effects of H₂SO₄ concentration, extractant concentration, and temperature on the metal extraction were investigated systematically. It was found that the extraction of metal ions by DEHAMP decreases in the following order: Ce(IV) > Th(IV) > Sc(III) > other RE(III). A possible extraction mechanism was proposed and the extracted complexes as Ce(SO₄)₂·2L and Th(HSO₄)₂SO₄·L were determined by the slope analysis method. Thermodynamic parameters (ΔH, ΔG, and ΔS) were calculated. The extraction reactions of Ce(IV) and Th(IV) were each exothermic processes. The loaded Ce(IV) and Th(IV) can be stripped efficiently by 3% H₂O₂ and 4 mol/L HCl, respectively. The extraction capacity of 0.63 mol/L DEHAMP is 30.0 g/L CeO₂ and 24.4 g/L ThO₂, respectively. Furthermore, a solvent extraction process to selectively extract and recover cerium and thorium from bastnaesite leaching was proposed, by which the purities of cerium and thorium products reached 97.2% and 96.5% with a yield of 85.4% and 98.8%, respectively.     

Solvent Extraction Investigations on Pu(IV) and Th(IV) Complexes with Hydrophilic SO3-Ph-BTP and SO3-Ph-BTBP Ligands

ABSTRACT

Complexation of Pu(IV) and Th(IV) cations by the title ligands – hydrophilic sulfophenyl triazinyl derivatives of bis-triazinyl-pyridine and -bipyridine – was studied in solvent extraction systems containing a TODGA extractant and one of these hydrophilic ligands. Stoichiometries and stability constants of the complexes formed in an acidic (HNO₃) aqueous phase have been determined. The Pu(IV) complexes are significantly stronger than their Th(IV) analogues. Only two complexes of each metal with SO₃-Ph-BTP (1:1 and 1:2) have been detected, and only one (1:1) with SO₃-Ph-BTBP; both numbers being less than expected based on the coordination numbers of the metal ions and on the denticities of the ligands. Possible reasons of this discrepancy are discussed.     

New Multi‐Dentate Ion‐Selective AXAD‐16‐MOPPA Polymer for the Preconcentration and Sequential Separation of U(VI), Th(IV) from Rare Earth Matrix

Abstract

A new class of multi‐dentate ligand anchored polymeric resin has been synthesized by grafting Amberlite XAD‐16 with [2‐(1‐Methyl‐3‐oxo‐2‐phenyl‐2, 3‐dihydro‐1H‐pyrazol‐4‐ylcarbamoyl)‐ethyl]‐phosphinic acid (AXAD‐16‐MOPPA). The modification steps involved during the grafting process are characterized by FT‐IR spectroscopy, ³¹P and ¹³C‐CPMAS (cross‐polarized magic angle spin) NMR spectroscopy, CHNPS elemental analysis and thermogravimetric analysis. The influence of various physio‐chemical parameters on the quantitative extraction of metal ions by the resin phase are studied and optimized by both static and dynamic methods. The developed grafted polymer shows greater selectivity for actinide ions like U(VI) and Th(IV) when compared to the lanthanides with greater distribution ratio values in highly acidic matrices. However, the lanthanides compete for the active sites in near neutral conditions. But the sorbed actinide ions and lanthanide elements can be separated by the sequential elution methodology. Moreover, the polymer exhibits faster metal ion phase exchange kinetics, where with a high sample flow rate of 25 mL min^?1 quantitative analyte sorption is achievable during the extraction chromatographic column operation for all the analytes. It also offers good ion‐selectivity and greater preconcentration factor values of 400 for U(VI) and 333 for Th(IV) in 4M HNO₃ conditions. The resin shows very high sorption capacity values of 1.45 mmol g^?1 for U(VI), 1.39 mmol g^?1 for Th(IV), and 1.31 mmol g^?1 for La(III) at near neutral conditions. Finally, the developed grafted resin has been successfully applied in extracting Th(IV) from matrix monazite sand which comprises large rare earth matrix, U(VI) from seawater and also U(VI) and Th(IV) from simulated nuclear spent fuel mixtures. The analytical data obtained from triplicate measurements are within 3.5% rsd, reflecting the reproducibility and reliability of the developed method.     

Elution Behavior of Metal Ions with Mixed Glycine-Nitric Acid Eluents in Dowex 50W-X8 Column: Separation of Th(IV), Ce(IV), Bi(III), Fe(III), and Al(III)

Abstract

Distribution coefficients (K) determined by the batch technique in acidic glycine media using Dowex 50W-X8 cation exchanger (H⁺?form, 100–200 mesh size) revealed that this medium can effectively be employed to separate a number of tetravalent and trivalent metal ions from bivalent metal ions. In fixed glycine (0.40 M) and varying concentration of nitric acid (0.10 to 1.0 M), a number of mixtures containing two or three metal ions were resolved on columns using about 8 g of exchanger. In 0.40 M glycine-1.0 M HNO₃ medium, Th(IV)/Ce(IV) were separated from Al(III)/Fe(III)/Bi(III)/Co(II)/Ni(II)/Cu(II)/Zn(II)/Cd(II)/Hg(II)/Pb(II)/Ag(I) and also Al(III)/Bi(III) from a number of divalent metal ions. In 0.40 M glycine-0.50 M HNO₃ medium, the resolution of following ternary mixtures were also achieved: Th(IV)/Ce(IV)-Al(III)/Bi(III)-Fe(III)/Co(II)/Ni(II)/Cu(II)/Zn(II)/Cd(II)/Hg(II)/Pb(II)/Ag(I). Th(IV)/Al(III)/Fe(III)/Bi(III) were also separated from other divalent metal ions in 1.60 M glycine-0.50 M HNO₃ medium. The values of K, elution characteristics of metal ions, elution curves, and the results of the resolution of a number of mixtures of metal ions along with standard deviations are reported.     

Extraction of Uranium(VI) and Plutonium(IV) with Tetra-Alkylcarbamides

ABSTRACT

The use of tetra-alkylcarbamides as novel extractants for the separation of uranium(VI) and plutonium(IV) by solvent extraction from spent nuclear fuels is investigated in this study. Batch extraction experiments show that tetra-alkylcarbamides strongly extract U(VI) with high distribution ratios. Plutonium(IV) can be co-extracted with U(VI) at high nitric acid concentration, while high U(VI)/Pu(IV) selectivities can be reached at lower acidity. Loading capacity experiments with high uranium concentrations show that alkyl chains longer than butyl are necessary to avoid third phase formation. Nevertheless, the viscosity of uranium-loaded solvents gets too high with alkyl chains longer than pentyl. Overall, this study shows that with TPU extractant (with four pentyl chains), an efficient co-extraction of uranium and plutonium can be reached (D_U,Pu > 1) for a concentration of nitric acid higher than 4 mol?L^?1, while the partition between uranium(VI) and plutonium(IV) could be operated even at 2 mol?L^?1 nitric acid without redox chemistry.     

Synergistic Extraction of U(VI), Th(IV), and Lanthanides(III) from Nitric Acid Solutions Using Mixtures of TODGA and Dinonylnaphthalene Sulfonic Acid

The extraction of U(VI), Th(IV), and lanthanides(III) from aqueous nitric acid solutions with mixtures of N,N,N′,N′-tetra(n-octyl)diglycolamide (TODGA) and dinonylnaphtalene sulfonic acid (HDNNS) in n-decane has been investigated. The extraction efficiency of U(VI), Th(IV), and Ln(III) ions is greatly enhanced by addition of HDNNS to an organic phase containing TODGA. The synergistic effect arises from the higher hydrophobicity of U(VI), Th(IV), and Ln(III) extracted species formed by TODGA and DNNS^? anions as compared to those formed by TODGA and NO₃^? ions as counter anions. The synergistic effect for U(VI), Th(IV), and Ln(III) extraction from aqueous nitric acid solutions with mixtures of TODGA and HDNNS becomes weaker when the acidity of the aqueous phase increases. A high synergistic enhancement is accompanied with a high selectivity of Ln(III) extraction from nitric acid solutions.     

SOLVENT EXTRACTION OF URANIUM(VI) AND THORIUM(IV) WITH A TETRA-CARBOXYLATED CALIX[4]ARENE AND EFFECT OF ALKALI IONS (Na+, K+)

ABSTRACT

The solvent extraction of uranium(VI) and thorium(IV) with a tetra-carboxylated calix[4]arene (LH₄) in chloroform has been studied in the presence or absence of alkali ions (M⁺=Na⁺, K⁺). When studied alone, UO₂ ²⁺ and Th⁴⁺ were extracted into chloroform as 2:2 and 1:1 metal:ligand complexes, respectively. The efficiency of extraction increases in the presence of alkali ions, due to the formation of heteronuclear complexes. For uranium(VI), the extracted species are found to be both 2:2:2 and 1:1:1 (uoi₂ ²⁺:M⁺:LH₄,) mixed complexes. For Th(IV) in the presence of Na⁺, the formation of a mixed complex in 1:1:1 (Th(IV):Na⁺:LH₄,) proportions has been evidenced. However, the exact nature of this species could not be determined. In practical grounds, LH. may be useful as a selective extracting agent for Th(IV) with respect to U(VI) since separation factor Th(IV)/U(VI) close to 1000 have been measured in competitive extraction, in the presence or absence of alkali ions.     

Coupled Transport of Zr(IV) through Tri-n-butylphosphate-Xylene-Based Supported Liquid Membranes

Abstract

The transport of Zr(IV) through tri-n-butylphosphate-xylene-based liquid membranes, supported in a polypropylene hydrophobic microporous film, has been studied. The concentration of HNO₃ in the feed solution and tri-n-butylphosphate (TBP) carrier in the membrane were varied, and the flux and permeability coefficients were determined. The optimum conditions found for maximum flux were determined to be 10 mol/dm³ HNO₃ and 2.93 mol/dm³ TBP with a flux value of 12.9 × 10^?6 mol · m^?2 · s^?1. The solvent extraction study revealed that 1.25 to 3.5 protons are involved in zirconium transport, and that two molecules of TBP are involved in the complex formation. The value of protons involved varies with acid concentration. The zirconium ion transport is coupled with nitrate ions transport.     

Amberlite XAD‐2 Impregnated with Cyanex302 for Separation of Traces of Thorium(IV)

Abstract

Amberlite XAD‐2 resin impregnated with Cyanex302 has been used to separate and preconcentrate thorium(IV) from associated elements prior to its spectrophotometric determination. The impregnated resin (HL‐XAD‐2) was characterized by IR spectra. A column packed with HL‐XAD‐2 was used to understand sorption and desorption behaviour of thorium(IV). The effect of various parameters such as acidity of aqueous phase, nature and concentration of eluting agents, eluent volume and its flow rate were evaluated to optimize conditions for isolation of thorium(IV). Adsorption characteristics of thorium(IV) on HL‐XAD‐2 in batch studies indicated that the data fit well in Langmuir and Freundlich adsorption isotherm models. The maximum sorption capacity of the modified resin for thorium(IV) was 8.48 mmol g^?1 while the limit of detection (3σ_B) was 0.75 µg dm^?3. A preconcentration factor greater than 100 was achieved. The influence of diverse ions on extraction of thorium(IV) was examined and the method developed was applied for the separation of thorium(IV) from synthetic mixtures and monazite sand. The method is reproducible with a relative standard deviation (R.S.D.) of 0.6%.     

Cation‐exchange kinetics and electrical conductivity studies of an ‘organic‐inorganic’ composite cation‐exchanger: Polypyrrole Th(IV) phosphate

Polypyrrole Th(IV) phosphate, an electrically conducting ‘organic‐inorganic’ cation‐exchange composite material was prepared by the incorporation of an electrically conducting polymer, i.e., polypyrrole, into the matrix of a fibrous type inorganic cation‐exchanger thorium(IV) phosphate. The composite cation‐exchanger has been of interest because of its good ion‐exchange capacity, higher chemical and thermal stability, and high selectivity for heavy metal ions. The temperature dependence of electrical conductivity of this composite system with increasing temperatures was measured on compressed pellets by using four‐in‐line‐probe dc electrical conductivity measuring instrument. The conductivity values lie in the semiconducting region, i.e., in the order of 10^?6 to 10^?4 S cm^?1 that follow the Arrhenius equation. Nernst–Plank equation has been applied to determine some kinetic parameters such as self‐diffusion coefficient (D₀), energy of activation (E_a), and entropy of activation (ΔS*) for Mg(II), Ca(II), Sr(II), Ba(II), Ni(II), Cu(II), Mn(II), and Zn(II) exchange with H⁺ at different temperatures on this composite material. These results are useful for predicting the ion‐exchange process occurring on the surface of this cation‐exchanger. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Gel-Liquid Extraction and Separation of U(VI), Th(IV), Ce(lll), and Co(ll)

Abstract

The gel-liquid extraction of U(VI), Th(IV), Ce(III), and Co(II) has been investigated in the 0.01 to 2 M HNO₃ range using a gel prepared by swelling styrene divinylbenzene with di-(2-ethylhexyl)phosphoric acid. Obtained results indicate that all of the tested cations can be extracted and that the extraction coefficients increase in the order Ce(III) < Co(II) < Th(IV) < U(VI) and generally decrease with acidity. Under suitable conditions, separation of Th(IV), Ce(III), or Co(II) from U(VI) or of Th(IV) from Ce(III) can be achieved. Kinetic studies indicate that the extraction process is controlled by a progressive shell sorption mechanism.     

Double O,C,O-chelated diorganotin(IV) cation

The synthesis of double O,C,O-chelated diorganotin(IV) compound L₂SnBr₂ (1), where L is 2,6-(MeOCH₂)₂C₆H₃^?, the precursor for the synthesis of Sn ← O intramolecularly coordinated organotin(IV) cations is reported. Treatment of compound 1 with SnBr₄ yielded the double O,C,O-chelated diorganotin(IV) ionic pair [L₂SnBr]⁺ [SnBr₅·THF]^? (2). Both compounds 1 and 2 were characterized by ¹H, ¹³C, ¹¹⁹Sn NMR and molecular structure of compound 2 was established by X-ray diffraction.     

Separation and Spectrophotometric Determination of Osmium(IV) and Ruthenium(III) with O-methoxyphenyl Thiourea as Chromogenic Legand: Sequential Separation of Osmium(IV), Ruthenium(III), and Platinum(IV)

A precise and selective method has been developed for extraction spectrophotometric determination of osmium(IV) and ruthenium(III) using o-methoxyphenyl thiourea (OMePT) as a chromogenic ligand. The basis of the proposed methods are osmium(IV)-OMePT complex was formed in 0.8 mol L^?1 at room temperature while ruthenium(III)-OMePT complex was formed in 3.4 mol L^?1 aqueous hydrochloric acid media after 5.0 min heating in boiling water bath. The osmium(IV)-OMePT and ruthenium(III)-OMePT complex were measured at 518 and 640 nm against the reagent blank, respectively. Complexes were also extracted in 10 mL chloroform and showed comparable absorbance values. Beer’s law was obeyed up to 110.0 μg mL^?1 for osmium(IV)-OMePT complex and up to 50.0 μg mL^?1 for ruthenium(III)-OMePT complex. Molar absorptivity and Sandell’s sensitivity of osmium(IV)-OMePT and ruthenium(III)-OMePT complexes were 2.12 × 10³ L mol^?1 cm^?1, 0.089 μg cm^?2 and 2.34 × 10³ L mol^?1 cm^?1, 0.043 μg cm^?2, respectively. The stoichiometry of osmium(IV)-OMePT and ruthenium(III)-OMePT complex was 1:1 and 1:2, respectively. Stability of osmium(IV)-OMePT complex was > 8 days and that of ruthenium(III)-OMePT complex was > 48 h. The proposed method was successfully applied for determination of osmium(IV) and ruthenium(III) from synthetic mixtures corresponding to platinum-osmium alloy and fissium alloy, respectively. The method was successfully applied for sequential separation of osmium(IV), ruthenium(III), and platinum(IV).     

Distribution Studies of Actinides Using a Tetradentate Extractant, 4,4′-Nonanedioyl-Bis(2,4-Dihydro-5-Methyl-2-Phenyl-3H-Pyrazol-3-One)

Abstract

The extraction of Th(IV), UO₂(II), Am(III), and Eu(III) from aqueous acid by a tetradentate extractant, 4,4′-nonanedioyl-bis(2,4-dihydro-5-methyl-2-phenyl-3H-pyrazol-3-one), H₂NDBP, has been studied and compared with two bidentate model compounds, 4-hexanoyl-2,4-dihydro-5-methyl-2-phenyl-3H-pyrazol-3-one, HHMPP, and 4-benzoyl-2,4-dihydro-5-methyl-2-phenyl-3H-pyrazol-3-one, HBMPP. The distribution coefficients of UO₂(II), Am(III), and Eu(III) were somewhat larger using H₂NDBP relative to the model compounds under the conditions studied. However, the Th(IV) extraction using H₂NDBP was greatly enhanced when compared to HBMPP or HHMPP. The distribution coefficient for Th(IV) from 0.5 M HNO₃ was 11.6 using 3.0 × 10^?3 M H₂NDBP compared with values of D < 0.01 using 3.0 × 10^?3 M HBMPP or HHMPP.     

Comparative Evaluation of Tri-n-butyl Phosphate (TBP) and Tris(2-ethylhexyl) Phosphate (TEHP) for the Recovery of Uranium from Monazite Leach Solution

Separation of U(VI) from Th(IV) and rare earth elements (REEs) present in monazite leach solution (nitric acid medium) has been studied using tris(2-ethylhexyl) phosphate (TEHP) and tri-n-butyl phosphate (TBP) dissolved in n-paraffin as solvents under varying experimental conditions such as nitric acid, extractant and metal ion concentrations etc. There is an increase in distribution ratio of U(VI) (D _U ) with increase in aqueous phase acidity up to 5 M HNO₃ beyond which a decrease is observed. Typically for 1 × 10^?3 M U(VI), the D_U values increase from 8 (0.5 M HNO₃) to 80 (5 M HNO₃) for 1.1 M TEHP, and from 2 (0.5 M HNO₃) to 43 (5 M HNO₃) for 1.1 M TBP in n-paraffin. The separation factors of U(VI) (β: D_U/D_M) over metal ions (M) such as Th(IV) and Y(III) (chosen as a representative of heavy REEs) are better for TEHP than TBP at all nitric acid concentrations. Batch solvent extraction data have been used to construct the McCabe-Thiele diagrams for the recovery of U(VI) employing TEHP as the extractant. A process flow sheet has been proposed with 0.2 M TEHP in n-paraffin as solvent for the recovery of U(VI) from simulated monazite leach solution in HNO₃ medium.