Extraction of Lanthanides with N,N′‐Dimethyl‐N,N′‐diphenyl‐malonamide and ‐3,6‐dioxaoctanediamide

Abstract

The extraction properties of the trivalent lanthanides (Ln(III)) with the bidentate N,N′‐dimethyl‐N,N′‐diphenyl‐malonamide (MA) and the tetradentate N,N′‐dimethyl‐N,N′‐diphenyl‐3,6‐dioxaoctanediamide (DOODA) were investigated. These diamides formed by coupling two amide groups with methylene and/or ether groups are bidentate for the MA and tetradentate for the DOODA. By adding a previous data regarding the tridentate N,N′‐dimethyl‐N,N′‐diphenyl‐diglycolamide (DGA), these extraction results enabled us systematically study an effect of number of oxygen donor on its extraction behavior of Ln(III). The change in the distribution ratios (Ds) of Lu(III) with an increase in the HNO₃ concentration is greater than that of La(III) in both the MA and DOODA systems. Therefore, the relationship between the D and atomic number, i.e., the lanthanide pattern, changes with the HNO₃ concentration: the Ds decrease with an increasing atomic number at lower HNO₃ concentrations. The Ds of the lighter Ln(III) are similar to the Ds of the heavier Ln(III) at higher HNO₃ concentrations. The number of the extractant in the extracted species for La(III) and Lu(III) obtained from slope analysis at 4 M HNO₃ in the MA system are about 3, while those in the DOODA system are quite different, i.e., 2 for La(III) and 1.5–3 for Lu(III). The comparison of the extractability of Ln(III) by MA, DOODA, and DGA shows that the magnitude of the Ds is in the sequence of MA < DOODA ? DGA. This suggests the introduction of one ether oxygen atom to the principal chain in the diamides leads to a good extractability for the Ln(III) from HNO₃ solution.     

Solvent extraction behavior of trivalent metal ions in diglycolamides having same carbon to oxygen ratio

Various diglycolamides (DGAs), N,N,N’,N’-tetraoctyl diglycolamide (TODGA), N,N-di-2-ethylhexyl-N’,N’-di-octyl diglycolamide (DEHDODGA), N,N,N’,N’-tetra-2-ethylhexyl diglycolamide (TEHDGA), N,N-di-decyl-N’,N’-di-hexyl diglycolamide (D²DHDGA), N,N-di-butyl-N’,N’-di-dodecyl diglycolamide (DBD³DGA), N,N,N’,N’-tetra-hexyl diglycolamide (THDGA), and N,N,N’,N’-tetradecyl diglycolamide (TDDGA) have been synthesized and studied for the extraction of Am(III) and Eu(III) from nitric acid medium. An attempt was made to understand the extraction and third phase formation behavior of trivalent metal ions in these DGAs. Our results revealed that despite having the same carbon to oxygen ratio in these DGAs, the third phase formation behavior and extractions achieved in these DGAs are significantly different.     

Water Soluble PDCA Derivatives for Selective Ln(III)/An(III) and Am(III)/Cm(III) Separation

The synthesis and solvent extraction behavior of dipicolinic acid (pyridine-2,6-dicarboxylic acid, PDCA) and their derivatives have been studied for possible use in selective back-extraction of actinides, especially americium. The extraction was performed from an organic phase containing a mixture of trivalent actinides and lanthanides pre-extracted with N,N,N’,N’-tetraoctyl diglycolamide (TODGA). The efficiency of the back-extraction was enhanced when the picolinate platform was used in a heterocyclic decadentate ligand called h₄tpaen. Beyond selective An/Ln extraction, the aqueous soluble h₄tpaen ligand seemed a potential reagent for an intra-group Am(III)/Cm(III) separation with a separation factor SF_Cm/Am of about 3.5.     

Modified Diglycolamides for the An(III) + Ln(III) Co-separation: Evaluation by Solvent Extraction and Time-Resolved Laser Fluorescence Spectroscopy

The use of two recently developed diglycolamide-based extractants for the co-separation of trivalent actinides (An(III)) and lanthanides (Ln(III)) is described and compared to the well-known extractant TODGA (N,N,N’,N’-tetraoctyl diglycolamide). The addition of one or two methyl groups to the central methylene carbon atoms of the TODGA molecule leads to a reduction of the extraction efficiency for An(III) and Ln(III). This is attributed to a lower complex formation constant, which was proven by Time-Resolved Laser Fluorescence Spectroscopy (TRLFS). Conditional stability constants were determined by solvent extraction and TRLFS. The reduction in extraction efficiency leads to overall reduced distribution ratios of all tested metal ions, including Sr(II). The reduced Sr(II) extraction is beneficial as a co-extraction in a solvent extraction process could be avoided, while an efficient extraction of the desired An(III) and Ln(III) is still achieved. Furthermore, this might be a benefit, as the stripping behavior might be improved, even at moderate nitric acid concentrations. The slightly higher affinity of the diglycolamides towards Eu(III) over Am(III) is represented by all ligands, although the selectivity is rather low. This results in promising extraction properties of the modified diglycolamides towards the development of continuous solvent extraction processes.     

Comparative Evaluation of CMPO and Diglycolamide Based Solvent Systems for Actinide Partitioning in Mixer-Settler Runs Using Tracer-Spiked PHWR Simulated High Level Waste

The TRUEX solvent (0.2 M CMPO + 1.2 M TBP) was employed for countercurrent extraction studies with radiotracers spiked pressurized heavy water reactor simulated high level waste (PHWR-SHLW) employing a 12-stage of mixer-settler. The results of the mixer-settler runs with CMPO were compared with those obtained under identical conditions employing TODGA (N,N,N’,N’-tetraoctyl diglycolamide) and T2EHDGA (N,N,N’,N’-tetra-2-ethylhexyl diglycolamide) as the extractants. Even though the TRUEX solvent revealed quantitative extraction of trivalent actinides and lanthanides in 5 stages at O/A = 1, stripping of the extracted metal ions from the loaded organic phase was poor with dilute HNO₃ solution (0.2 M HNO₃). Quantitative stripping could not be achieved in 12 stages even when a complexing solution (0.1 M citric acid + 0.1 M HNO₃) was employed as the strippant. In contrast, the stripping from loaded TODGA and T2EHDGA solvents was possible in < 6 stages with 0.2 M HNO₃. The experimental results suggested that the performance of TRUEX solvent was inferior to the diglycolamide based extractants such as TODGA and T2EHDGA.     

Supercritical Fluid Dissolution and Extraction of Trivalent Metal Cations from Different Matrices

Studies on the recovery of trivalent metal ions such as Nd³⁺Eu³⁺ (taken as homologs of Am(III)) from solid oxide (Nd₂O₃), Thorium concentrate (obtained from Monazite ore processing), tissue paper/surgical gloves (rubber), and plant samples have been carried out by supercritical fluid extraction (SFE) using supercritical CO₂ and ethanol/nitric acid. N,N,N’,N’-tetraoctyl diglycolamide (TODGA) was used as the extractant in these studies. The results showed that the recovery of Nd increased with TODGA concentration from 50% (no TODGA) to 70% (10% TODGA) at 3 M HNO₃ in ethanol. However, the extraction of Nd at 1 M HNO₃ was invariant with 1-3% (v/v) TODGA concentration (73 ± 4%). Interestingly, REEs recovery from Th concentrate was ? 60% even without TODGA using ethanol/3 M HNO₃ mixture. On the other hand, quantitative recovery of ^152,154Eu from tissue paper and surgical gloves sample could be achieved using 3 M HNO₃/ethanol mixture. This suggested that it would be possible to decontaminate the contaminated laboratory waste papers using SFE technique.     

Synergistic Extraction of Lanthanides (III) with Mixtures of TODGA and Hydrophobic Ionic Liquid into Molecular Diluent

The extraction of lanthanides(III) from aqueous nitric acid solutions with N,N,N’,N’-tetra(n-octyl)diglycolamide (TODGA) and with mixtures of TODGA and the hydrophobic ionic liquid (IL) [C₄mim][Tf₂N] into 1,2-dichloroethane (DCE) has been investigated. The extraction efficiency of Ln(III) ions was greatly enhanced by the addition of a small amount of IL to an organic phase containing TODGA. The synergistic effect comes from the higher hydrophobicity of Ln(III) extracted species formed by TODGA and the weakly coordinating Tf₂N^? anions compared with those formed by TODGA and NO₃^? ions as the counter-anions. The partition of Tf₂N^? anions between the organic and aqueous phases is the dominant factor governing the extractability of lanthanides(III) with mixtures of TODGA and [C₄mim][Tf₂N]. The extraction of Ln(III) from aqueous nitric acid solutions by TODGA alone and its mixtures with [C₄mim][Tf₂N] into DCE can be described on the basis of the solvation extraction mechanism. However, in the extraction system with added [C₄mim][Tf₂N], the partition of Tf₂N^? between two immiscible phases and the interaction between HTf₂N and TODGA in the organic phase should be taken into account. Possible reasons of the antagonistic effect in the TODGA–[C₄mim][Tf₂N] extraction system are discussed.     

Synergistic Extraction of Lanthanides in a Liquid-Liquid Countercurrent Centrifugal Extractor

We have developed a liquid-liquid countercurrent centrifugal extractor that induces Taylor vortices in the annular fluid region. To demonstrate extraction of multiple species (Nd/Sm/Eu/Gd/Dy) with N,N,N′,N′-tetraoctyl diglycolamide (TODGA), additional chemical agents, such as a surfactant (sodium bis(2-ethylhexyl) sulfosuccinate (AOT)), a synergist (nonanoic acid) and a masking agent (N,N,N′,N′-tetraethyl-3,6-dioxaoctane-1,8-diamide (DOODA(C2))) were employed. When only TODGA was utilized, extraction performance was not effective due to the insufficient dispersion even under a high rotating speed. By combining TODGA and other chemical agents, the separation performance was improved considerably in the countercurrent flow of aqueous and organic phases due to the synergistic effect and improved dispersion.     

Liquid – Liquid Extraction and Pertraction of Eu(III) from Nitric Acid Medium Using Several Substituted Diglycolamide Extractants

Solvent extraction and supported liquid membrane (SLM) transport properties of Eu(III) from nitric acid feed conditions were investigated using several substituted diglycolamide (DGA) extractants such as N,N,N′N′-tetra-n-octyl diglycolamide (TODGA), N,N,N′N′-tetra(2-ethylhexyl) diglycolamide (T2EHDGA), N,N,N′N′-tetra-n-hexyl diglycolamide (THDGA), N,N,N′N′-tetra-n-pentyl diglycolamide (TPDGA), and N,N,N′N′-tetra-n-decyl diglycolamide (TDDGA). Effects of feed acidity and phase modifier composition on Eu(III) extraction were investigated using the DGAs and the nature of extracted species were ascertained by slope analysis method. The Eu(III) distribution ratio (D_Eu) values were found to decrease in the presence of iso-decanol. In general, the D_Eu values decreased with increased alkyl chain length of the DGA. The extracted species contained only 2 extractant molecules when TPDGA and TDDGA were used while for TODGA about four extractant molecules were found to be present in the extracted species.

The supported liquid membrane transport of Eu(III) was studied under varying experimental conditions using the five DGA extractants. Transport studies using 0.1 M DGA as the extractant suggested the trend as TDDGA > TODGA > T2EHDGA ～ THDGA which significantly changed to TPDGA > THDGA > TODGA > TDDGA > T2EHDGA in the presence of 30% iso-decanol as the phase modifier. The permeability coefficient (P) values were also determined with membranes of varying pore sizes.     

The Effect of Alkyl Substituents on Actinide and Lanthanide Extraction by Diglycolamide Compounds

The effect of the alkyl substituents on amidic N atoms in diglycolamide (DGA) compounds on solvent extraction has been investigated. The solubility in water and n-dodecane, lanthanide loading capacity, and distribution ratios (D) of lanthanides and actinides for various DGA compounds are reported. DGA derivatives with short alkyl chains, for example, methyl and ethyl groups, are very water soluble, while DGA derivatives with long alkyl chains, for example, octyl (TODGA), decyl (TDDGA), dodecyl (TDdDGA), and 2-ethylhexyl (TEHDGA) group are moderately soluble in n-dodecane. DGA derivatives with phenyl substituents have very low solubility in both aqueous and organic solvents, which suggests that these compounds will not be suitable for solvent extraction applications in the HNO₃/n-dodecane systems. The lanthanide loading capacities of DGA extractants correlate with their alkyl chain lengths according to the following order: TDdDGA > TDDGA > TODGA > TEHDGA. The branched-alkyl-chain DGA derivative (TEHDGA) exhibits both lower D and loading capacity than TODGA. The results of masking-effect and solubility tests indicate that TEDGA is the best actinide masking agent among the water-soluble DGA derivatives tested. Actinide and lanthanide extractions using ten DGA compounds in six diluents (nitrobenzene, 1,2-dichloroethane, 1-octanol, chloroform, toluene, and n-dodecane) are also reported; it was observed that lipophilic DGA derivatives with shorter alkyl chains show higher D values.     

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.     

Actinide–lanthanide co-extraction by rigidified diglycolamides

Within the actinide and lanthanide co-extraction strategy, three rigidified diglycolamides, namely 2,6-bis (N-dodecyl-carboxamide)-4-oxo-4H-pyran (1), 2,6-bis-[N-(4-tert-butylphenyl)carboxamide]-4-oxo-4H-pyran (2), 2,6-?bis[(N-docecyl-N-methyl)carboxamide]-?4-methoxy-?tetrahydro-pyran (3), were synthesized. Moreover, the effect of structural rigidification on Am(III) and Eu(III) extraction under different conditions was investigated. The carboxamide extractant 3 resembles the extracting behavior of N,N,N′,N′‐tetraoctyl diglycolamide (TODGA) in terms of efficiency and affinity within the lanthanide family, together with fast kinetics and satisfactory cation back-extraction. The presence of 1-octanol in the diluent mixture strongly affects the ligand stability. Moreover, despite the low extraction efficiency showed by 1 and 2, all the three ligands exhibit a higher affinity for Am with respect to TODGA, resulting in a lower lanthanide/Americium separation factor, of around 4 for ligand 3 and close to 1 for ligands 1 and 2.     

Simultaneous Extraction of Neodymium and Uranium using Hollow Fiber Supported Liquid Membrane

Simultaneous extraction of neodymium and uranium ions from aqueous nitrate media was investigated using hollow fiber supported liquid membrane (HFSLM). The organic phase supported in the membrane pores consisted of extractant N,N,N’,N’-tetraoctyl diglycolamide (TODGA), phase modifier isodecanol, and diluent n-dodecane. Experimental results suggest that there is competition between neodymium and uranium ions for complexation with TODGA. The initial rate of extraction of Nd³⁺ ions was found to be approximately six times to that of UO₂²⁺ ions. Experimental data was explained by a mathematical model for simultaneous transport of two metal ions. The model results were found to be in good agreement with the experimental data when the diffusivities of neodymium-TODGA complex (D_nm) and uranium-TODGA complex (D_um) in the membrane pore are 1.1 x 10^?11 and 4 x 10^?12 m²/s, respectively.     

Radiolytic Stability of N,N,N′,N′-Tetraoctyl Diglycolamide (TODGA) in the Presence of Phase Modifiers Dissolved in n-Dodecane

The radiolytic stability of a promising extractant for actinide partitioning from high-level radioactive liquid waste, namely N,N,N',N'-tetraoctyl diglycolamide (TODGA) was investigated in the presence of several phase modifiers, viz. N,N-dihexyloctanamide (DHOA), tri-n-butyl phosphate (TBP), 1-decanol, and iso-decanol dissolved in n-dodecane. The distribution ratio of Am(III) decreased with increased radiation dose studied up to 1000 kGy. Nevertheless, all the compositions of extractants showed fairly high extraction of Am(III) up to 500 kGy (D_Am: ≥ 50), beyond which significant decrease was observed. However, the D_Am values were sufficiently high for process applications for the chosen compositions even at an absorbed dose of 1000 kGy. The stripping behavior of Am(III) with 0.2 M HNO₃ was found to be favorable with increased absorbed dose by the solvent up to 1000 kGy. With an increased absorbed dose, the loading of Nd(III) in the organic phase decreased due to depletion of ligand/extractant concentration (TODGA) in the organic phase. There was marginal variation in the hydrodynamic parameters such as density, viscosity, and interfacial tension (IFT) of the irradiated solvents vis-a-vis fresh/unirradiated solvent.     

Transport of lanthanides and fission products through supported liquid membranes containing N,N,N′,N′-tetraoctyl diglycolamide (TODGA) as the carrier

Facilitated transport of trivalent lanthanides, viz. La(III), Eu(III), Lu(III) and several fission product elements such as Tc, Mo, Zr, Pd, I, Cs and Ru across a flat sheet supported liquid membrane made of PTFE impregnated with N,N,N′,N′-tetraoctyl diglycolamide (TODGA) in n-dodecane was investigated from dilute nitric acid solutions. The transport rates of lanthanides increased with nitric acid concentration in a manner similar to their distribution ratios. The trend in metal ion transport after 75 min followed the order: La > Eu > Lu > Zr > Sr > I > Pd ~ Tc > Ru > Mo ~ Cs, which was consistent even after 5 h of operation. However, the transport of I reached the maximum value of ~26% in 100 min and remained constant thereafter. In the case of Am(III) transport studies, excellent decontamination from Zr was achieved when 0.4 M oxalic acid was added to the feed solution.     

Extraction of Pr(III), Nd(III), and Dy(III) from HTFSA Aqueous Solution by TODGA/Phosphonium-Based Ionic Liquids

The extraction behavior of rare earth (RE) elements using N,N,N′,N′-tetraoctyl diglycolamide (TODGA) in an ionic liquid (IL) system was investigated by slope analyses. Metallic salts of Pr(III), Nd(III), and Dy(III) with bis(trifluoromethylsulfonyl)amide (TFSA) were synthesized and studied for their extraction mechanism. The selected concentration of TODGA was diluted with triethylpentylphosphonium bis(trifluoromethylsulfonyl)amide ([P₂₂₂₅][TFSA]) to prepare an extracting phase for the slope analyses. The stoichiometry of RE(III) was determined in order to estimate the extracted species. Furthermore, the complexation state of the extracted species was evaluated by spectroscopic analyses, including Fourier-transform infrared (FT-IR) spectroscopy, Raman spectroscopy, and ultraviolet–visible (UV–Vis) spectroscopy. The FT-IR and Raman spectra were estimated using density functional theory (DFT) calculations. Thorough analysis of the FT-IR spectrum was carried out in order to assign the TODGA group that mainly coordinated the metal ion. The solvation of the [TFSA]^? anion in the coordination sphere of [Nd(TODGA)_(2–3)]³⁺ was investigated by Raman spectroscopic analysis. The coordination ability of TODGA was investigated from the peak shift of the hypersensitive transition (⁴I_9/2→²G_7/2) in UV–Vis spectroscopic measurements. From electrochemical analysis, the extracted [Nd(TODGA)₃]³⁺ complex in [P₂₂₂₅][TFSA] was found to be reduced as per the following reaction: [Nd(TODGA)₃]³⁺ + 3e^? → Nd(0) + 3[TODGA] at ?3.0 V, and the diffusion coefficient of [Nd(TODGA)₃]³⁺ was calculated to be 1.6 × 10^?11 m² s^?1 at 373 K. The direct electrodeposition of the extracted [Nd(TODGA)₃]³⁺ in [P₂₂₂₅][TFSA] at 373 K allowed us to conclude that the middle layer of Nd electrodeposits was the metallic state, while a part of the top surface was the oxidation state by XPS analysis.     

Applications of Diglycolamide Based Solvent Extraction Processes in Spent Nuclear Fuel Reprocessing,Part 1: TODGA

Over the last decade there has been much interest in the applications of diglycolamide (DGA) ligands for the extraction of the trivalent lanthanide and actinide ions from PUREX high active raffinates or dissolved spent nuclear fuel. Of the DGAs, the N,N,N’,N’-tetraoctyldiglycolamide (TODGA) is the best known and most widely studied. A number of new actinide separation processes have been proposed based on extraction with TODGA. This review covers TODGA-based processes and extraction data, specifically focusing on how phase modifiers have been used to increase metal loading and thus enhance the operating process envelopes. Effects of third phase formation and the organic phase speciation are reviewed in this context. Relevant aspects of the extraction chemistry of important solvents (TODGA-modifier-diluent combinations) are described and their performances demonstrated by a consideration of the published flowsheet tests. It is seen that modifiers are successfully enabling the use of TODGA in actinide separation processes but to date the identification and testing of suitable modifiers has been rather empirical. There is a growing understanding of the fundamental chemistry occurring in the organic phase and how that affects extractant speciation and metal loading capacity but studies are still needed if TODGA-based flowsheets are to become an industrially deployable option for minor actinide (MA) recovery processes.     

An Additional Insight into the Correlation between the Distribution Ratios and the Aqueous Acidity of the TODGA System

Abstract

Extraction of Eu(III) and Am(III) from HNO₃ into the organic solvents using N,N,N′,N′‐tetraoctyl‐diglycolamide (TODGA) was investigated in order to study the detailed extraction reaction. The chemical species: 1:2 for metal:TODGA complex is present in polar diluents. On the other hand, the metal complexes need three or more TODGA molecules to remain stable in non‐polar diluents. The HNO₃ concentration dependence on the distribution ratio suggests that HNO₃ participates in the metal extraction. Infrared spectra indicate that the carbonyl oxygen coordinates with Eu(III), and luminescence lifetimes suggest that there are no water molecules in the inner coordination sphere of the extracted Eu‐complex.     

Nitric Acid Extraction into the TODGA/TBP Solvent

The tridentate diglycolamide ligand N,N,N′,N′-tetraoctyl diglycolamide (TODGA) shows many interesting properties and is a very good extractant for the minor actinides (MAs) and lanthanides but, due to its low loading capacity, requires a phase modifier when used in a solvent extraction process. Consequently, applications of TODGA in conjunction with tri-butyl phosphate (TBP) in novel DIAMEX and SANEX processes for recovering MAs have been reported. However, TODGA and TBP also extract nitric acid and this has a significant influence on process performance. Here new distribution data for the extraction of nitric acid into solvent phases containing TODGA and TBP have been collected and modeled using an equilibrium-based approach accounting for nitric acid activities in the aqueous phase. Models for the extraction of nitric acid using the individual extractants were obtained using a variety of complexes and these were then combined to give the extraction of the mixed TODGA and TBP solvent. Using this approach, the nitric acid extraction of the mixed TODGA/TBP system can be reliably reproduced indicating that no significant synergistic or antagonistic complexes are formed in solution.     

Synergistic Solvent Extraction of Lanthanides(III) with Mixtures of 4-benzoyl-3-methyl-1-phenylpyrazol-5-one and Some Novel Carbamoyl- and Phosphorylmethoxymethylphosphine Oxides

The solvent extraction of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y from weak acidic hydrochloric acid solutions into an organic phase containing 4-benzoyl-3-methyl-1-phenylpyrazol-5-one (HP) and neutral tridentate organophosphorus ligands R₂P(O)CH₂OCH₂C(O)NBu₂ R = Bu (I), R = Ph (II) and R₂P(O)CH₂OCH₂P(O)R¹₂ R = R¹ = Bu (III); R = Bu, R¹ = Ph (IV); R = R¹ = Ph(V) has been studied. A considerable synergistic effect was observed in the presence of HP in the organic phase containing tetraoctyldiglycolamide (TODGA) and neutral organophosphorus ligands I - V. A successive replacement of C(O)NAlk₂ groups in the diglycolamide extractant molecule by P(O)Ph₂ groups leads to an increase in the extraction efficiency of Ln(III) ions when toluene was used as diluent. Phosphoryl-containing podand I possess a higher extraction efficiency towards Ln(III) ions than TODGA. The extraction equilibrium was investigated and the equilibrium constants were calculated. It was found that the lanthanide(III) ions are extracted as LnLP₃ and LnL₂P₃ complexes with mixtures of HP and I in toluene from weak acidic solutions.