Extraction and separation of rare earths from chloride medium with mixtures of 2‐ethylhexylphosphonic acid mono‐(2‐ethylhexyl) ester and sec‐nonylphenoxy acetic acid

BACKGROUND: 2‐ethylhexylphosphonic acid mono‐(2‐ethylhexyl) ester (HEHEHP, H₂A₂) has been applied extensively to the extraction of rare earths. However, there are some limitations to its further utilization and the synergistic extraction of rare earths with mixtures of HEHEHP and another extractant has attracted much attention. Organic carboxylic acids are also a type of extractant employed for the extraction of rare earths, e.g. naphthenic acid has been widely used to separate yttrium from rare earths. Compared with naphthenic acid, sec‐nonylphenoxy acetic acid (CA100, H₂B₂) has many advantages such as stable composition, low solubility, and strong acidity in the aqueous phase. In the present study, the extraction of rare earths with mixtures of HEHEHP and CA100 has been investigated. The separation of the rare earth elements is also studied. RESULTS: The synergistic enhancement coefficient decreases with increasing atomic number of the lanthanoid. A significant synergistic effect is found for the extraction of La³⁺ as the complex LaH₂ClA₂B₂ with mixtures of HEHEHP and CA100. The equilibrium constant and thermodynamic functions obtained from the experimental results are 10^?0.92 (K_AB), 13.23 kJ mol^?1 (ΔH), 5.25 kJ mol^?1 (ΔG), and 26.75 J mol^?1 K^?1 (ΔS), respectively. CONCLUSION: Graphical and numerical methods have been successfully employed to determine the stoichiometries for the extraction of La³⁺ with mixtures of HEHEHP and CA100. The mixtures have different extraction effects on different rare earths, which provides the possibility for the separation of yttrium from heavy rare earths at an appropriate ratio of HEHEHP and CA100. Copyright © 2009 Society of Chemical Industry     

Solvent extraction studies of Sm(III) from nitrate medium and separation factors of rare earth elements with mixtures of sec‐octylphenoxyacetic acid and 1,10‐phenthroline

BACKGROUND: Liquid–liquid extraction is widely used for the separation of rare earths, among which synergistic extraction has attracted more and more attention. Numerous types of synergistic extraction systems have been applied to rare earths with high extraction efficiency and selectivities. In the present study, mixtures of sec‐octylphenoxyacetic acid (CA12, H₂A₂) and 1,10‐phenanthroline (phen, B) have been used for the extraction of rare earths from nitrate medium. The stoichiometry of samarium(III) extraction has been studied using the methods of slope analysis and constant molar ratio. The possibility of using synergistic extraction effects to separate rare earths has also been studied. RESULTS: Mixtures of CA12 and phen display synergistic effects in the extraction of rare earth elements giving maximum enhancement coefficients of 5.5 (La); 13.7 (Nd); 15.9 (Sm); 24.5 (Tb); 45.4 (Yb) and 12.3 (Y). Samarium(III) is extracted as SmHA₄B₃ with mixtures of CA12 and phen instead of SmHA₄ when extracted with CA12 alone. The calculated logarithm of the equilibrium constant is 6.0 and the thermodynamic functions, ΔH, ΔG, and ΔS, have been calculated as 4.3 kJ mol^?1, ? 33.7 kJ mol^?1 and 129.7 J mol^?1 K^?1, respectively. CONCLUSION: Mixtures of CA12 and phen exhibit synergistic effects on rare earth elements. Graphical and numerical methods have been successfully used to determine their stoichiometries. The different synergistic effects may provide the possibility of separating yttrium from heavy lanthanoids at an appropriate ratio of CA12 and phen. Copyright © 2010 Society of Chemical Industry     

Studies on the solvent extraction of rare earths from nitrate media with a combination of di‐(2‐ethylhexyl)phosphoric acid and sec‐octylphenoxyacetic acid

BACKGROUND: Di‐(2‐ethylhexyl)phosphoric acid (D2EHPA, H₂A₂) has been used extensively in hydrometallurgy for the extraction of rare earths, but it has some limitations. Synergistic extraction has attracted much attention because of its enhanced extractabilities and selectivities. In the present study, sec‐octylphenoxyacetic acid (CA12, H₂B₂) was added into D2EHPA systems for the extraction and separation of rare earths. The extraction mechanism of lanthanum with the mixtures and the separation of lanthanoids and yttrium were investigated. RESULTS: The synergistic enhancement coefficient for La³⁺ extracted with D2EHPA + CA12 was calculated as 3.63. La³⁺ was extracted as La(NO₃)₂H₂A₂B with the mixture. The logarithm of the equilibrium constant was determined as 0.80. The thermodynamic functions, ΔH, ΔG, and ΔS were calculated to be 4.03 kJ mol^?1, ? 1.96 kJ mol^?1, and 20.46 J mol^?1 K^?1, respectively. The mixtures have synergistic effects on Ce³⁺, Nd³⁺, and Y³⁺, with an especially strong synergistic effect on Y³⁺. Neither synergistic nor antagonistic effects on Dy³⁺ and weak antagonistic effects on Lu³⁺ were found. CONCLUSION: Mixtures of D2EHPA and CA12 exhibit evident synergistic effects when used to extract La³⁺ from nitric solution. The stoichiometries of the extracted complexes have been determined by graphical and numerical methods to be La(NO₃)₂H₂A₂B with the mixture. The extraction is an endothermic process. The mixture exhibits different extraction effects on rare earths, which provides possibilities for the separation of Y³⁺ from Ln³⁺ at a proper ratio of D2EHPA and CA12. Copyright © 2008 Society of Chemical Industry     

Synergistic extraction of rare earths(III) from chloride medium with mixtures of 1‐phenyl‐3‐methyl‐4‐benzoyl‐pyrazalone‐5 and di‐(2‐ethylhexyl)‐2‐ethylhexylphosphonate

The synergistic effect of 1‐phenyl‐3‐methyl‐4‐benzoyl‐pyrazalone‐5 (HPMBP, HA) and di‐(2‐ethylhexyl)‐2‐ethylhexylphosphonate (DEHEHP, B) in the extraction of rare earths (RE) from chloride solutions has been investigated. Under the experimental conditions used, there was no detectable extraction when DEHEHP was used as a single extractant while the amount of RE(III) extracted by HPMBP alone was also low. But mixtures of the two extractants at a certain ratio had very high extractability for all the RE(III). For example, the synergistic enhancement coefficient was calculated to be 9.35 for Y³⁺, and taking Yb³⁺ and Y³⁺ as examples, RE³⁺ is extracted as RE(OH)A₂.B. The stoichiometry, extraction constants and thermodynamic functions such as Gibbs free energy change ΔG (?17.06 kJ mol^?1), enthalpy change ΔH (?35.08 kJ mol^?1) and entropy change ΔS (?60.47 J K^?1 mol^?1) for Y³⁺ at 298 K were determined. The separation factors (SF) for adjacent pairs of rare earths were calculated. Studies show that the binary extraction system not only enhances the extraction efficiency of RE(III) but also improves the selectivity, especially between La(III) and the other rare earth elements. Copyright © 2006 Society of Chemical Industry     

Synergistic Extraction of Some Rare Earths(III) from Nitrate Media by Thenoyltrifluoroacetone and Tri-n-octylamine

Abstract

The synergistic action of tri-n-octylamine (TOA) in the selective extraction of the rare earths La, Nd, Tm, Lu, and Y with thenoyltrifluoroacetone (HTTA) was studied in a nitrate media (0.6 M HNO₃ + 11.6 g/L CaO). The synergism enhances the REE extraction and separation. The [HTTA], [TOA], diluent, complexing agents, and calcium ion effects were also studied.     

Synergistic Extraction and Separation of Heavy Lanthanide by Mixtures of Bis(2,4,4‐trimethylpentyl)phosphinic Acid and 2‐Ethylhexyl Phosphinic Acid Mono‐2‐Ethylhexyl Ester

Abstract

The extraction of Yb³⁺ from chloride solution has been studied using mixtures of bis(2,4,4‐trimethylpentyl)phosphinic acid (Cyanex272) and 2‐ethylhexyl phosphinic acid mono‐2‐ethylhexl ester (P507). The results show that Yb³⁺ is extracted into heptane as YbA₃(HA)₃ with Cyanex272, YbL₃(HL)₃ with P507, and YbA₂L₄H₃ with synergistic mixture. The equilibrium constants, formation constants, and thermodynamic functions have been determined. Extraction mechanism and extraction process are also proposed. The extraction of heavy lanthanide ions by mixtures of Cyanex272 and P507 is studied and the possibility of separating heavy rare earth ions is discussed.     

Synergistic Extraction of Trivalent Actinides by Mixtures of Thenoyltrifluoroacetone and Neutral Oxo Donors

Abstract

The synergistic extraction of trivalent actinides Am, Cm, Bk, and Cf has been studied by mixtures of HTTA and TOPO as well as DOSO in xylene at 30°C. HTTA-S (TOPO, DOSO) interaction corrections have been applied to calculate the “free” S concentrations in the organic phase. In the extraction of trivalent actinides, the third-power dependence on [HTTA]_org at a fixed [S]_org has been observed only after applying this correction. The synergistic species M(TTA)₃.S and M(TTA)₃.2S were found to be extracted into the organic phase whose stability constants (β₁, β₂, and K ₂) have been evaluated. Extraction by HTTA + S(S = TOPO, DOSO, TBP, TBTP) shows the order of extraction to be Tm > Cf > Bk > Eu > Pm > Am > Cm for the trivalent ions. The Am/Cm separation factor with the synergistic mixtures is ～3 whereas with HTTA alone it is ～6 when they are extracted from the chloroacetate buffer.     

Synergistic extraction and separation study of rare earth elements from nitrate medium by mixtures of sec‐nonylphenoxy acetic acid and 2,2′‐bipyridyl

BACKGROUND: Synergistic extraction has been proven to enhance extractability and selectivity. Numerous types of synergistic extraction systems have been applied to rare earth elements, among which sec‐nonylphenoxyacetic acid (CA100) has proved to be an excellent synergistic extractant. In this study, the synergistic enhancement of the extraction of holmium(III) from nitrate medium by mixtures of CA100 (H₂A₂) with 2,2′‐bipyridyl (bipy, B) in n‐heptane has been investigated. The extraction of all other lanthanides (except polonium) and yttrium by the mixtures in n‐heptane has also been studied. RESULTS: Mixtures of CA100 and bipy have significant synergistic effects on all rare earth elements, for example holmium(III) is extracted as Ho(NO₃)₂HA₂B with the mixture instead of HoH₂A₅, which is extracted by CA100 alone. The thermodynamic functions, ΔH^o, ΔG^o, and ΔS^o have been calculated as 2.96 kJ mol^?1, ? 6.23 kJ mol^?1, and 31.34 J mol^?1 K^?1, respectively. CONCLUSION: Methods of slope analysis and constant molar ratio have been successfully applied to study the synergistic extraction stoichiometries of holmium(III) by mixtures of CA100 and bipy. Mixtures of these extractants have also shown various synergistic effects with other rare earth elements, making it possible to separate them. Thus CA100 + bipy may be used to separate yttrium from other lanthanides at appropriate ratios of the extractants. Copyright © 2011 Society of Chemical Industry     

Extraction Theory and Form of the Extraction Complex of Terbium,Erbium, Ytterbium,and Lutecium in the Synergistic System Kerosene/HTTA/TBP/Dilute HNO3

Abstract

Analysis of extensive distribution data taken in the synergistic system kerosene/HTTA/TBP/dilute HNO₃ indicates that the rare earths terbium, erbium, ytterbium, and lutecium are extracted into the organic phase as M(NO₃)(TTA)₂(TBP)₂. The thermodynamic stability constants for the four metals in the two-phase system have been calculated to be 41 ± 10, 26 ± 10, 19 ± 10, and 14 ± 10%, respectively.     

Development of a solvent extraction process for production of nuclear grade dysprosium oxide from a crude concentrate

A solvent extraction process for the production of nuclear grade Dy₂O₃ for its applications in advance heavy water reactor (AHWR) from a crude concentrate of rare earths containing Y₂O₃ 67%, Dy₂O₃ 22%, etc. has been developed and tested by bench-scale counter-current operations. The challenging task of separating Dy₂O₃ from other rare earths with similar chemical properties has been successfully accomplished by adopting a dual cycle solvent extraction scheme based on an organophosphorus extractant 2-ethylhexylphosphonic acid, mono-2-ethylhexyl ester (EHEHPA). Taking the advantage of the extraction order of rare earths with EHEHPA, in the first cycle heavy rare earths including yttrium fractions are separated in the product strip solution, while dysprosium is concentrated in the raffinate solution along with terbium, gadolinium, etc. In the second cycle dysprosium is purified to the extent of >99.5% with respect to other rare earths from the dysprosium concentrate obtained in the raffinate of the first cycle. Effects of process variables such as aqueous acidity, phase ratio, metal concentration in the aqueous feed, scrubbing and stripping acidity etc on separation of yttrium and other heavy rare earths in the first cycle and upgrading the purity of Dy₂O₃ in the second cycle have been evaluated. Under optimized conditions of process parameters, continuous operations of mixer settler yielded kilogram quantity of nuclear pure Dy₂O₃ which exceeds the specifications required. The recovery was found to be >98%. The overall process also produces two concentrates as by-products namely yttrium (>93%, 1st cycle) and terbium (>54%, 2nd cycle) as source materials for further upgradation of these elements.     

Solvent Extraction Studies of Rare Earths from Thiocyanate Medium with N,N,N´,N´-tetra(2-ethylhexyl) diglycolamide

The extraction behavior of rare earth (RE) elements from thiocyanate medium by N,N,N^’,N^’-tetra(2-ethylhexyl) diglycolamide (TEHDGA), a neutral extractant, has been investigated and the optimum conditions for their separations were determined. Isodecyl alcohol was used as phase modifier and a concentration of 5%(v/v) was found sufficient to mitigate third phase formation under our experimental conditions. The extraction mechanism of RE with TEHDGA was established by analyzing distribution data with slope analysis technique and showed the formation of a neutral species, RE(SCN)₃.2TEHDGA, in the organic phase. The extraction of rare earth decreased with increase in temperature indicating exothermic nature and the enthalpy change (ΔH) obtained for Y(III) was ?14.27 kJ/mol. Among various stripping agents studied, oxalic acid was found to be efficient in quantitative stripping of rare earths from TEHDGA. The extraction efficiency for all the rare earths by TEHDGA was also investigated. High separation factor of 6.4 for Er/Y pair at 0.03 M thiocyanate has indicated the feasibility of using TEHDGA as extractant to separate Y from heavy rare earths, in particular Er, from thiocyanate medium.     

Extraction of rare earths using mixtures of sec-octylphenoxy acetic acid and organophosphorus acids

The extraction of rare earths from nitrate medium using three organophosphorus acids, 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (HEHEHP), di-(2-ethylhexyl) phosphoric acid (D2EHPA), bis(2,4,4-trimethylpentyl) phosphinic acid (Cyanex272), and their mixtures with sec-octylphenoxy acetic acid (CA12) has been studied in detail. The mixtures have different extraction effects on various rare earths. Synergistic extraction effects are only found when light rare earths and yttrium (III) are extracted with mixtures of D2EHPA and CA12. The possibilities of separating the rare earths with these mixtures are investigated according to the extractabilities. It is feasible and advantageous to separate yttrium (III) from the lanthanoids (III) with HEHEHP + CA12 and D2EHPA+CA12 mixtures at proper extractant ratios. The separation of yttrium (III) from heavy rare earths is also possible with mixtures of Cyanex272 and CA12.     

SYNERGISTIC SOLVENT EXTRACTION OF TRIVALENT LANTHANIDES AND ACTINIDE BY MIXTURES OF 1-PHENYL-3-METHYL-4-BENZOYL-PYRA2ALONE-5 AND NEUTRAL OXO-DONORS

ABSTRACT

The synergistic solvent extraction of trivalent lanthanides such as La, Eu and Lu and a trivalent actinide, Am, has been studied with mixtures of 1-phenyl-3-methyl-4-benzoyl-pyrazalone-5 (HPMBP) and bis(2-ethylhexyl) sulphoxide (B2EHSO) or octyl(phenyl)-N,N-di isobutylcarbamoylmethylphosphine oxide (CMPO) in xylene. The extraction data have been analysed by both graphical and theoretical methods by taking into account aqueous phase speciation and all plausible complexes extracted into the organic phase. With HPMBP alone all the trivalent metal ions form M(PMBP)₃.HPMBP type self adducts. With B2EHSO as a neutral donor, the synergistic adduct species are M(PMBP)₃.B2EHSO and M(PMBP)₃.2 B2EHSO (where M = La, Eu, Lu and Am), whereas with CMPO as a neutral donor the only complex extracted into the organic phase is M(PMBP)₃.CMPO. The synergistic extraction constants of the above species which were deduced by non-linear regression analysis are found to increase monotonically with decreasing ionic radii of these metal ions.     

Synergistic Effects in the Extraction of Uranium(VI) by Di-4-octylphenyl Phosphoric Acid

Abstract

The extraction of uranium(VI) from sulfuric acid solutions by di-4-octylphenyl phosphoric acid (DOPPA) is enhanced by the addition of neutral organophosphorus compounds due to synergistic action. The effect of tri-n-butyl phosphate (TBP), dibutylbutyl phosphonate (DBBP), and tri-n-octyl phosphine oxide (TOPO) was studied. The synergistic effect increased in this order. In the case of TBP and DBBP the extraction coefficient for U(VI) decreased with increasing concentration of synergistic agent after reaching a maximum. With TOPO, on the other hand, there was an increase even after this limit. This was because of the extraction of uranium by TOPO itself. The effect of uranium loading in the organic phase on the synergistic behavior was studied and the results were compared with those obtained with di-2-ethylhexyl phosphoric acid (DEHPA) in the presence of the same synergistic agents. The results with these two extractants indicate that with TOPO the synergism is mainly due to the formation of substitution products of the type UO₂A₂B₂ and with TBP addition products of the type UO₂(HA₂)₂B.     

EXTRACTION AND SEPARATION OF HEAVY RARE EARTH(III) WITH EXTRACTION RESIN CONTAINING DI(2,4,4-TRIMETHYL PENTYL) PHOSPHINIC ACID (CYANEX 272)

ABSTRACT

Extraction resins, of the type of Levextrel, (which is a collective term for styrene/divinylbenzene based copolymers of predominantly macroporous structure that contain a selective extractant) are important for the recovery and separation of metal ions, as they combine features of solvent extraction and ion exchange resins. This paper presents the results of the adsorption of heavy rare earth ions (Ho(III), Er(III), Tm(III), Yb(III), Lu(III) and Y(II1)) from hydrochloric acid solutions at 0.2 mol/L ionic strength and 50°C by the extraction resin containing di (2,4,4-trimethyl pentyl) phosphinic acid (Cyanex 272) and the chromatographic separation of (Er(III), Tm(III) and Yb(III)). Technological separation products, with purity and yield of Tm₂O3 >99.97%, >80%; Er₂O₃ >99.9%, >94% and Yb₂O₃ >99.8%, >80% respectively, have been obtained from a feed having the composition Tm₂O₃ 60%, Er₂O₃ 10%, and Yb₂O₃ 3%, the others 27%.

The distribution coefficients, extraction equilibrium constants and separation factors have been determined as a function of acidity, loading of the resin and rare earths, flow rates and column ratios. The resolutions and efficiencies of separation of Er/Tm/Yb each other have been calculated. The stoichiometry of the extraction of rare earth ions has been suggested as well.     

Synergistic Extraction of Trivalent Actinides by Mixtures of 1-Phenyl-3-methyl-4-benzoyl-pyrazolone-5 and Neutral Oxo Donors

Abstract

The synergistic extraction of trivalent actinides Am, Cm, Bk, and Cf with mixtures of 1-phenyl-3-methyl-4-benzoyl-pyrazolone-5 (HPMBP) and TBP or TOPO has been investigated in xylene at 30°C. With HPMBP alone, all four trivalent actinides form M(PMBP)₃· HPMBP-type self-adducts. Bk(III) shows an abnormally high extraction with HPMBP alone. With TBP or TOPO(S) as neutral donor, except in the Bk/HPMBP/TBP system where Bk(PMBP)₃· HPMBP·TBP was extracted, all metal ions were extracted as M(PMBP)₃·S and M(PMBP)₃·(S)₂ into the organic phase. The equilibrium constants (β₁, β₂, and K ₂ for the organic phase synergistic reactions have been calculated. The β₁, β₂ values for Bk(III)/HPMBP/TOPO system are much lower as compared to the corresponding values for other trivalent actinides. The reasons for this extraordinary behavior of Bk(III) have been discussed. The extraction behavior of the M(III)/HPMBP/S and the M(III)/HTTA/S systems has also been compared.     

Synergistic Solvent Extraction of Lanthanides (III) with Mixtures of Tetraphenylmethylenediphosphine Dioxide and Picrolonic Acid from HCl Solutions

The solvent extraction of lanthanides(III) from hydrochloric acid solutions into the organic phase containing neutral bidentate extractant tetraphenylmethylenediphosphine dioxide (L) and picrolonic acid (HP) has been studied. A considerable synergistic effect was observed in the presence of HP in the organic phase containing neutral bidentate organophosphorus ligand. The extraction equilibrium was investigated and the equilibrium constants were calculated. It was found that the lanthanide(III) ions are extracted from weak acidic solutions as LnP₃L and LnP₃L₂ complexes. The mixture L–HP offers higher extraction efficiency toward Ln(III) than mixtures of L with 1-phenyl-3-methyl-4-benzoyl-pyrazolone-5 or picric acid.     

EXTRACTION SYSTEMS USING BIS-1,2-0ICARBCILYLC0BALTATE ANO POLYOXONIUM COMPOUNDS FOR LANTHANIOE SEPARATIONS

ABSTRACT

The extraction of rare earths (lanthanides, Y, Sc) by voluminous bis-1,2-dicarbollylcobaltate anions disolved in nitrobenzene and in a nitrobenzene - carbon tetrachloride mixture has been investigated and the exchange extraction constants for both solvents, individual extraction constants anddG for ion transfer across the water - nitrobenzene phase boundary has been determined. Extraction decreases with increasing atomic number of the lanthanide.

The influence of several polyoxonium compounds on the distribution ratios and the extraction selectivity has been investigated. In the extraction systems with bis-1,2-dicarbollylcobaltate - 18-crown-6 in nitrobenzene, synergism was found for the light lanthanides but antagonism was observed for the heavy ones. The overall separation factor is Ctla/10 compared to in the absence of crown la/²     

TEMPERATURE EFFECT ON THE SYNERGISTIC SOLVENT EXTRACT ION OF LANTHANOIDES

The synergistic solvent extraction of Pr, Gd and Yd with mixtures of HTTA and Aliquat 336 in CCl₄C₆H₆ and CHCl₃ at 288,298,308 and 318 K has been studied. The values of the equilibrium constants as well as the values of the thermodynamic parameters have been calculated.