Extraction Of Gadolinium Research Articles

Improvement of Gd(III) Solvent Extraction by 4-Benzoyl-3-methyl-1-phenyl-2-pyrazolin-5-one: Non-Aqueous Systems

The study of the liquid–liquid extraction of gadolinium (Gd(III) ion) with a chelating compound, 4-benzoyl-3-methyl-1-phenyl-2-pyrazolin-5-one (HP), and the determination of the process parameters are presented by employing two ionic liquids, namely, ([C1Cnim+][Tf2N−], n = 4, 10) and CHCl3, as diluents. Compared to CHCl3, the ionic liquid offers increased distribution ratios in an aqueous medium. A step forward, enhanced solvent extraction, and improved separation upon the addition of ethylene glycol are demonstrated, i.e., a boost of two immiscible organic phases, compared to traditional aqueous solutions. However, this is noticeable when using CHCl3, but unfortunately not with ionic liquid combination, [C1C10im+][Tf2N−]. Several conclusions are given, highlighting the role of the ionic diluent in complexation processes and selectivity with an employment of the chelating agent HP for various metal s-, p-, d-, and f-cations, i.e., nearly 25 metals. A detailed evaluation of the selectivity between these metals was made when changing both the aqueous phase completely with ethylene glycol or partially with glycerol (1:1). Electron paramagnetic resonance (EPR) spectroscopy has been used to study the established chemical species in the obtained organic extracts, such as Gd3+, Fe3+, Cu2+, and Cr3+, with unpaired electrons.

Electrochemical extraction of gadolinium on Sn electrode and preparation of Sn-Gd intermetallic compounds in LiCl-KCl melts

For the development of nuclear energy, it is important to remove the fission products which hinder nuclear reactions. In this paper, Gd was extracted by an electrochemical method in LiCl-KCl molten salts. The electrochemical reactions of GdCl3 and SnCl2 are measured by a series of electrochemical means. Three kinds of Sn-Li and four Sn-Gd alloys are obtained by cyclic voltammetry and other electrochemical means. Thermodynamic and kinetic parameters of electrode processes for Gd(III) and Sn(II) ions are calculated by different electrochemical test methods. The diffusion coefficient and diffusion activation energy of the Sn(II) ion are reactions as 2.23–3.78 × 10-5 cm2 s-1 and 24.4 kJ mol-1, respectively. Thermodynamic parameters of Sn3Gd intermetallic compounds were calculated based on open circuit chronopotentiometry at different temperatures (ΔHf0(Sn3Gd)=−229.225kJmol-1 and ΔSf0(Sn3Gd)=−38.2Jmol-1K-1). Metallic Gd is extracted by potentiostatic and galvanostatic electrolysis on liquid Sn electrode in melts, respectively. According to X-ray diffraction (XRD) and scanning electron microscopy and elemental dispersive spectrometry (SEM-EDS), the products are mainly composed of the intermetallic compound Sn3Gd and Sn metal. The experimental results show that the fission element Gd can be extracted with high extraction rate by electrolysis in molten salt system.

Insights into non-aqueous solvent extraction of gadolinium and neodymium from ethylene glycol solution using Cyanex 572

Comparison of the separation factors for Gd(III) over Nd(III) extraction from aqueous and non-aqueous ethylene glycol solutions using Cyanex 572 in kerosene. • Addition of water bridges the gap between hydrometallurgy and solvometallurgy. • Extraction of Gd(III) and Nd(III) from non-aqueous solution was compared with aqueous solution. • Gd and Nd extraction increases with increasing Cyanex 572 extractant concentrations. • Temperature had almost no effect on the extraction of both metal ions. • Under certain conditions, maximum separation factor was obtained and reached 22.09. The reprocessing of rare earth elements (REEs) by conventional hydrometallurgical processes remains a challenge because of the difficulties of separation. Solvometallurgy is a new non-aqueous solvent extraction approach including two immiscible organic phases which has been advanced for the extraction of rare earths. The less polar organic phase (LP) was a solution of Cyanex 572 (Cy-572) as an acidic extractant dissolved in kerosene. Whereas, the more polar organic phase (MP) was ethylene glycol with a limited amount of water dissolved in metal nitrate salts and lithium nitrate as a salting-out agent. The extraction of Gd(III) and Nd(III) from ethylene glycol solution was compared with extraction from an aqueous solution. The solvent extraction equilibrium was estimated by slope analysis method, and the composition of the Gd(III) extracted species in the less polar phase was proposed to be Gd(OH) L 2 . 2 HL ¯ . The non-aqueous system performs better separation of rare earths than the corresponding conventional extraction system. Subsequently, 0.1 mol/L HCl is the best stripping agent for both metal ions after two steps from the less polar phase, while a solution composed of 10% HF + 0.05 mol/L HCl is superior for nearly complete separation between the two elements. Eventually, the separation of binary mixtures of Gd(III) and Nd(III) is possible by this new non-aqueous solvent extraction system. A complete flow sheet process including extraction, scrubbing and stripping steps for the separation of Gd(III) and Nd(III) was proposed.

Synthesis of Dihexyldithiophosphate Ligand and a Preliminary Study on Its Use for the Extraction of Gadolinium from Rare Earth Elements Mixture

Development of body imaging techniques for medical diagnosis has future promising. To improve the image visibility, Gadolinium (Gd) has been known as an important material for preparing the contrast agent. However, since the rare earth metals have unique physical properties, the separation of Gd from the other metals by a simple, effective and efficient method is still challenging. Hereby, we report the separation of Gd from the rare earth mixture with dihexyl dithiophosphate (DHDTP) ligand by solvent extraction method. The amount of Gd before and after the extraction process was determined with ICP-OES. The results show that the extraction efficiency for the mixed samples of Gd (III) and Sm (III) is 53.10% with 51.10% purity of Gd (III) and extraction efficiency for mixed samples of Gd (III) and Dy (III) is 93.82% with 50.35% purity of Gd (III). This result indicates that DHDTP can be used for solvent extraction of Gd.

Selective extraction of gadolinium using free-standing imprinted mesoporous carboxymethyl chitosan films with high capacity

Novel imprinted mesoporous carboxymethyl chitosan films (IMCFs) were investigated in detail. When acting as adsorbents, imprinted mesoporous carboxymethyl chitosan films with highly ordered chiral nematic structures, exhibit efficient adsorption for gadolinium ions (Gd(III)). The maximum adsorption capacity of IMCFs calculated from Langmuir isotherm model was 25.372 mg g−1 at pH 7.0. Due to the presence of highly selective imprinted sites, chitosan films possess significant selectivity for Gd(III), compared with other rare earth ions. More importantly, carboxymethyl chitosan films could be retrieved conveniently and quickly without extra operations, which greatly promote their recycling. Reusability tests further demonstrated films can be considered as stable and reliable adsorbents, enhancing their potential industrial applications.

Extraction of gadolinium on Cu electrode from LiCl-KCl melts by formation of Cu-Gd alloys

Electrochemical behavior of gadolinium was studied on W and Cu electrodes in LiCl-KCl melts 823 K via cyclic voltammetry, square wave voltammetry, and open circuit chronopotentiometry. The reduction of Gd(III) ions was found to be through a one-step process: Gd(III) + 3e− = Gd(0). The equilibrium potential of the Gd(III)/Gd(0) redox couple was measured via open circuit chronopotentiometry in the temperature range of 773–893 K, with subsequent calculation of the apparent standard potential, $$ {E}_{\mathrm{Gd}\left(\mathrm{III}\right)/\mathrm{Gd}(0)}^{\ast 0} $$ , and the apparent Gibbs free energy of formation for GdCl3, $$ \varDelta {G}_f^{\ast 0}\left({\mathrm{GdCl}}_3\right) $$ . Three reduction peaks, corresponding to the formation of GdxCuy intermetallic compounds, were detected from cyclic voltammogram and square wave voltammogram obtained by co-reduction of Gd(III) and Cu(II) ions or electrodeposition of Gd(III) on Cu electrode. Potentiostatic/galvanostatic electrolysis was performed on Cu electrode with different electrolytic conditions. The results indicate that the Cu-Gd alloys are comprised of CuGd, Cu2Gd, and Cu6Gd phases. The morphology and micro-zone chemical analysis of the deposits were characterized by scanning electron microscopy (SEM) equipped with energy dispersive spectrometry (EDS). The highest extraction efficiency of metallic Gd could reach about 99.60% at − 2.20 V for 12 h at 823 K. Therefore, employing electrochemical deposition of Gd(III) on reactive Cu electrode to extract Gd is feasible.

Evaluation of the emulsion liquid membrane performance on the removal of gadolinium from acidic solutions

This work evaluates the performance of emulsion liquid membrane (ELM) for the extraction of gadolinium(III) from acidic solution. The ELM was made up of di-(2-ethylhexyl) phosphoric acid (D2EHPA) as carrier, Span 80 (sorbitol monooleate) as emulsifying agent, commercial kerosene as organic diluent and Nitric acid as stripping phase. Important physical and chemical variables affecting the ELM performance for the extraction of gadolinium(III) such as carrier concentration, mixing time, surfactant concentration, agitation speed, initial pH of the feed phase, internal phase concentration, treatment ratio, and feed phase concentration were systematically investigated. Results indicated that the highest gadolinium(III) extraction can be attained after 10 min of mixing by using 0.05 M D2EHPA, 1.5% (v/v) Span 80, 1.0 M nitric acid as stripping phase at feed phase pH of 2, agitation speed of 180 rpm, and treatment ratio of 1:10. At the optimum condition, simultaneous quantitative extraction (>99%) and stripping (>79%) of gadolinium were achieved. Furthermore, the overall mass transfer coefficient was calculated and the results revealed that the extraction was interfacially controlled.

Extraction of Gd3+ and UO22+ Ions Using Polystyrene Grafted Dibenzo Crown Ether (DB18C6) with Octanol and Nitrobenzene: A Molecular Dynamics Study

Atomistic molecular dynamics (MD) simulations are performed in order to derive thermodynamic properties important to understand the extraction of gadolinium (Gd3+) and uranium dioxide (UO2) with dibenzo crown ether (DBCE) in nitrobenzene (NB) and octanol (OCT) solvents. The effect of polystyrene graft length, on DBCE, on the binding behavior of Gd3+ and UO22+ is investigated for the first time. Our simulation results demonstrate that the binding of Gd3+ and UO22+ onto the oxygens of crown ethers is favorable for polystyrene grafted crown ether in the organic solvents OCT and NB. The metal ion binding free energy (ΔGBinding) in different solvent environments is calculated using the thermodynamic integration (TI) method. ΔGBinding becomes more favorable in both solvents, NB and OCT, with an increase in the polystyrene monomer length. The metal ion transferability from an aqueous phase to an organic phase is estimated by calculating transfer free-energy calculations (ΔGTransfer). ΔGTransfer is significantly favorable for both Gd3+ and UO22+ for the transfer from the aqueous phase to the organic phase (i.e., NB and OCT) via ion-complexation to DBCE with an increase in polystyrene length. The partition coefficient (log P) values for Gd3+ and UO22+ show a 5-fold increase in separation capacity with polystyrene grafted DBCE. We corroborate the observed behavior by further analyzing the structural and dynamical properties of the ions in different phases.

Study on the Electrochemical Co-Reduction of Gd(III) and Al(III) in LiF-CaF2 Melt

This paper describes the co-reduction process of Gd-Al alloys and the electrochemical extraction of gadolinium from gadolinium oxide in LiF-CaF2 melt. Gd2O3 was fluorinated by adding AlF3, and dissolved into the melt as Gd(III). The electrochemical behaviors and alloy forming mechanisms of Gd(III) and Al(III) were analyzed through cyclic voltammetry, square wave voltammetry, chronopotentiometry, and open circuit chronopotentiometry. Potentiostatic electrolyses in the LiF-CaF2-Gd2O3-AlF3 system were conducted for three hours under −1.60 V and −2.20 V, respectively, and at least three kinds of Gd-Al alloys were obtained. The GdAl3 phase was identified through a scanning electron microscope equipped with an energy dispersive spectrometer (SEM-EDS) and X-ray diffraction analysis, and GdAl2 and GdAl were characterized by SEM-EDS.

Application of emulsion nanofluids membrane for the extraction of gadolinium using response surface methodology

In this work, an emulsion nanofluid membrane (ENM) was applied to effectively extract gadolinium. Simultaneous emulsification of nanoparticles and surfactant was performed to stabilize the ENM. Multi-walled carbon nanotubes (MWCNTs) nanofluid was employed as liquid membrane. The ENM composed of diisooctylphosphinic acid (CYANEX 272) as carrier, MWCNTs as nanoparticles, Span-85 (sorbitan triooleate) as surfactant, kerosene as organic diluent and nitric acid as internal phase. The effects of important operating variables i.e., carrier concentration, MWCNTs concentration, surfactant concentration, mixing speed, internal phase concentration and feed phase pH were investigated. Response surface methodology (RSM), according to central composite design (CCD), is used to optimize the process variables and a regression model for extraction percentage was developed. The 3D response surfaces of gadolinium (III) extraction efficiency were achieved and significance of six important variables and their interactions on extraction efficiency were found out. The desirability function was performed to simultaneously evaluate all the factors and determine the best possible goals for each response. The optimum condition for gadolinium extraction were: The optimum condition for gadolinium extraction were: 0.84M of CYANEX 272, MWCNTs concentration of 318.05ppm, 2.91% (v/v) of Span-85, mixing speed of 188.15rpm, 1.27M of HNO3 as internal phase reagent, feed phase pH of 3 and desirability value of 0.904. Under the optimized condition, the extraction of Gadolinium (III) reached the maximum of 92.05%.

Solvent extraction of gadolinium (III) from hydrochloric acid solutions with cationic extractants D2EHPA and Ionquest 801

The solvent extraction of gadolinium (III) from hydrochloric acid solutions with cationic extractants D2EHPA and Ionquest 801 dissolved in Exxsol D100 was investigated. The study was carried out with concentrated solutions in order to better reproduce industrial process conditions. The following operational variables were investigated: initial concentration of gadolinium (16–40 g L−1, i.e., 0·104–0·255 mol L−1), initial concentration of extractant (0·5–1·5 mol L−1), initial pH of the aqueous phase (1–5) and aqueous/organic volumetric ratio (0·5–2·0). Data fitting including the statistical analysis of the estimated equilibrium parameters indicated that gadolinium (III) is extracted from hydrochloric acid solutions with D2EHPA and Ionquest 801 according to the overall reaction Gd3++3(HX)2⇆GdX3(HX)3+3H+. The apparent equilibrium constant at 298±1 K was found to be 1·9±0·3 for the system Gd(III)–D2EHPA and 0·028±0·003 for the system Gd(III)–Ionquest 801.

Extraction of gadolinium from El-Garra El-Hamra rare-earth cake, South Western Desert, Egypt

The study area of El-Garra El-Hamra is one of the igneous masses located in the southern part of the Western Desert of Egypt. This work has been carried out to investigate the process of gadolinium separation from REEs cake obtained from El-Garra El-Hamra ore concentrate. It is considered as a new approach in the Nuclear Materials Authority of Egypt. Firstly; the optimum leaching conditions achieved are 200 gm/L H2SO4, 1/2 solid/liquid ratio, 4 h agitation time,−125 mesh size and at 90 °C temperature. Then by solvent extraction method using 1 mol/L D2EHPA middle REEs were extracted. The organic extractant was stripped by using 2 mol/L HCl and Gd pregnant solution was obtained. Then, the relevant optimum factors were 0.3 mol/L D2EHPA diluted by kerosene, 10 min contact time, and 4/1 organic/aqueous ratio giving 87 % Gd extraction. Then, the scrubbing of the loaded extractant was by 1 mol/L HCL followed by Gd stripping using 5 M HCl, contact time of 30 min and 1/3 organic/aqueous ratio. The strip solution was subjected to evaporation and little amount was dried to obtain GdCl3 powder having a purity of about 81 % associated with YCl3 4 %.

Selective extraction of gadolinium from Sm2O3 and Gd2O3 mixtures in a single step assisted by MgCl2 in LiCl–KCl melts

The chloration of MgCl2 was studied in the LiCl–KCl–MgCl2–Gd2O3–Sm2O3 melts. Gd(III) and Sm(III) ions were observed by cyclic voltammetry and square wave voltammetry assisted by MgCl2 in melts. X-ray diffraction (XRD) patterns of melts indicated Gd2O3 and Sm2O3 were chlorinated by MgCl2 and formed GdCl3 and SmCl3. XRD patterns of non-dissolved residues, which were left after the melts were washed with water to remove the soluble salt, showed that the new compounds (i.e., GdOCl, SmOCl, MgO, Gd(OH)3, and Sm(OH)3) were produced. Potentiostatic electrolysis experiments were performed to extract Gd from Gd2O3 and Sm2O3 mixtures assisted by MgCl2. Separation between Gd2O3 and Sm2O3 was also achieved in a single step with the formation of Mg–Li–Gd alloys. XRD patterns of alloys indicated that Mg3Gd phase was formed. Scanning electron microscope images with energy dispersive X-ray spectroscopy showed Gd elements were mainly distributed in the grain boundary.

Electroextraction of gadolinium from Gd2O3 in LiCl–KCl–AlCl3 molten salts

This work concerns directly the extraction of gadolinium from Gd2O3 by co-reduction with Al3+ in the LiCl–KCl–AlCl3 molten salts on the molybdenum and aluminum electrode, respectively, at temperature of 773K. Gibbs energy calculation shows that AlCl3 can favorably chloridize Gd2O3 and release Gd3+ ions. The electrochemical behaviors of Al3+, Gd3+ and the mechanisms of alloy formation were investigated by conducting a series of electrochemical techniques. Four typical signals were observed in cyclic voltammetry, square wave voltammetry and chronopotentiometry, while five plateaus were observed in open circuit chronopotentiometry, which might correspond to different kinds of Gd–Al intermetallic compounds. Potentiostatic and galvanostatic electrolysis were conducted to extract gadolinium from the LiCl–KCl–AlCl3 melts by the co-reduction method, and it was found that if the molybdenum cathode was used, GdAl2 particles would be deposited and adhere to a large amount of salt electrolytes. In contrast, when the aluminum plate was used as the cathode, a layer formed by potentiostatic electrolysis corresponding to an intermetallic compound (GdAl3) and three layers formed by galvanostatic electrolysis corresponding to three different Gd–Al intermetallic compounds such as GdAl3, GdAl2 and GdAl could be collected and identified through scanning electron microscopy (SEM)–energy dispersive X-ray (EDX) and X-ray diffraction (XRD) analysis. Besides, electroextractions of gadolinium by co-reduction with Al3+ on the aluminum electrode have been performed with extraction efficiency of 89.7% for potentiostatic electrolysis and 96.5% for galvanostatic electrolysis, respectively.

Synergistic extraction of gadolinium from nitrate media by mixtures of bis (2,4,4-trimethylpentyl) dithiophosphinic acid and di-(2-ethylhexyl) phosphoric acid

The extraction of gadolinium (III) from aqueous nitrate solution with bis (2,4,4-trimethylpentyl) dithiophosphinic acid (Cyanex301), di-(2-ethylhexyl) phosphoric acid (D2EHPA) and the mixtures of extractants was investigated. Various parameters affecting the extraction process including the pH of aqueous phase, nitrate ion, extractant concentration, temperature, and stripping agents were studied. The stoichiometric coefficients of reactive extraction, thermodynamic and equilibrium parameters were obtained for two extractants and their mixtures.The results showed that the extraction ability of Cyanex301 was lower than that of D2EHPA extractant. As a result, the extraction of Gd3+ at low concentration of Cyanex301 was investigated by the addition of D2EHPA to the extraction system. The reactive extraction in the mixture system was spontaneous in nature as referred to the negative sign of ΔG while it was not favorable in case of single Cyanex301 system as indicated by the positive sign of ΔG. The experimental results showed that the mixture of extractants provided better extraction efficiency and effective stripping performance in comparison with single D2EHPA or Cyanex301 system.

Solid-liquid extraction of Gd(III) and separation possibilities of rare earths from phosphoric acid solutions using Tulsion CH-93 and Tulsion CH-90 resins

Solid-liquid extraction of gadolinium was investigated from phosphoric acid medium using commercial amino phosphonic acid resin, Tulsion CH-93. The experimental conditions studied included equilibration time, acid concentration, mass of the resin, metal concentration, loading and elution. The percent extraction of Gd(III) was studied as a function of phosphoric acid (0.05-3 mol/L) using Tulsion CH-93 resin. The corresponding lgD vs. equilibrium pH plot gave straight line with a slope of 1.8. The percent extraction decreased with acid concentration increasing, conforming ion exchange mechanism. Under observed experimental conditions the loading capacity of Tulsion CH-93 for gadolinium was 10.6 mg/g. Among several eluants screened, the quantitative elution of Gd(III) from loaded Tulsion CH-93 was obtained with ammonium oxalate (0.15 mol/L). The extraction behavior of commonly associated metals with gadolinium was studied as a function of phosphoric acid concentration. Tulsion CH-93 resin showed selective extraction towards heavy rare earths (Lu and Yb) which could be separated from other rare earths at 3 mol/L H3PO4, similar to wet phosphoric acid (3–5 mol/L). On the other hand Gd(III) and other rare earths were studied with chelating resin Tulsion CH-90. Light rare earths were highly extracted and these could be separated from heavy rare earths and Gd.

Study on the Cloud Point Extraction of Gd(III) with 8-Hydroxyquinoline

The extraction of gadolinium was studied using Cloud Point Extraction (CPE) with 8-hydroxyquinoline (8-HQ) as a chelating agent. The structure of the extracted Gd3+ complex with 8-HQ in the micelle of Triton X114 was determined using log-log analysis of the extraction data. A ratio of 8-HQ to Gd3+ of 3:1 was found. The CPE results were compared with those obtained by classical liquid-liquid extraction with chloroform as solvent. The parameters of the extraction process in both media were determined and compared. A quantitative extraction of Gd3+ at pH 5.5 was obtained by CPE using a 8-HQ/Gd3+ ratio of 10 although a 8-HQ/Gd3+ ratio of 500 was necessary for solvent extraction using chloroform as solvent, illustrating an increase of the mass action of extractants when using CPE instead of solvent extraction. Under those conditions, a higher extraction constant was determined for CPE compared with solvent extraction even if the formation of adducts in the CPE system could not be checked experimentally.

Extraction of lanthanum and gadolinium(III) at the cloud point using p-sulfonatocalyx[n]arenes as chelating agents

The extraction of gadolinium(III) and lanthanum(III) ions at the cloud point is studied in Triton X100 micellar solutions in a wide range of pH. In the absence of chelating agents, lanthanum(III) and gadolinium(III) ions are unselectively extracted at pH > 6. It is shown that the use of p-sulfonatothiacalyx[6(8)]arenes as chelating agents noticeably enhances the degree of extraction at pH 2–6. The composition and stability of lanthanum-p-sulfonatothiacalyx[n]arene complexes (n = 4, 6, 8) are estimated in a wide range of pH by pH-potentiometry. The degree of Gd3+ and La3+ ions extraction, which is performed at the cloud points employing calyxarene macrocycles of different sizes, is depended on the acidity of a medium.

Equilibrium and kinetic studies on the extraction of gadolinium(III) from nitrate medium by di‐2‐ethylhexylphosphoric acid in kerosene using a single drop technique

AbstractThe liquid–liquid extraction of Gd(III) from aqueous nitrate medium was studied using di‐2‐ethylhexylphosphoric acid (HDEHP) in kerosene. On the basis of the slope analysis data, the composition of the extracted species was found to be [Gd A3(HA)] with the extraction equilibrium constant (Kex) = (1.48 ± 0.042) × 10−12 mol dm−3. The results of the effect of temperature on the value of the equilibrium extraction constant indicated the endothermic character of the extraction system. The kinetics of the forward extraction of Gd3+ from nitrate medium by HDEHP in kerosene was investigated using the single drop column technique. The rate of flux (mass transfer per unit area) was found to be proportional to [Gd(III)], [H2A2](o), [NO3−], and [H+]−1 in the liquid drop organic phase. The forward extraction rate constant, kf, was 2.24 × 10−3 m s−1 using the equation: Copyright © 2005 Society of Chemical Industry

Solvent extraction of lanthanide ions with 1-phenyl-3-methyl-4-benzoyl-pyrazolone-5 (HPMBP), III: Extraction of gadolinium(III), terbium(III), dysprosium(III), holimum(III), and thulium(III) byHPMBP from aqueous solutions

The solvent extraction behaviour of Gd(III), Tb(III), Dy(III), Ho(III), and Tm(III) has been investigated using 1-phenyl-3-methyl-4-benzoyl-pyrazolone-5 (HPMBP or HL) in carbon tetrachloride as the extractant. Depending on the concentration ofHPMBP in the organic phase the chelatesLnL3 [Ln(III)=Gd, Tb, Dy, Ho, Tm] and adductsLnL3 · HL [Ln(III)=Gd, Tb, Dy, Ho] were extracted. The extraction equilibrium constants (Kex3 orKex4) for the formation ofLnL3 orLnL3 · HL and the two-phase stability constants of the chelates or adducts (β 3 x , β 4 x ) have been evaluated.