CYANEX 923 AS AN EXTRACTANT FOR TRIVALENT LANTHANIDES AND YTTRIUM

ABSTRACT

The extraction of yttrium and some trivalent lanthanides from thiocyanate and nitrate solutions using Cyanex 923 { TRPO ) in xylene as an extractant has been investigated. It has been found that these trivalent metal ions are extracted from thiocyanate solution as M(SCN)₃.n TRPO ; n in general having the values of 4 and 3 for the lighter and the heavier lanthanides respectively. On the other hand, from nitrate solutions these trivalent metal ions are extracted as M(NO₃)₃ 3 TRPO. The equilibrium constants of the extracted complexes have been obtained by non-linear regression analysis. In both the thiocyanate and nitrate systems, the distribution ratios of trivalent lanthanides are found to increase with decreasing ionic radii and the distribution ratio of yttrium lies along with those of the middle lanthanides. The separation factors between these trivalent metal ions were evaluated and compared with those obtained using commercially important extraction reagents like tributylphosphate (TBP), trioctylphosphine oxide (TOPO) and di-2-ethylhexylphosphoric acid (DEHPA). The separation possibilities between yttrium and the trivalent lanthanides have also been discussed.     

Rapid Solvent Extraction of Uranium(VI) with N-Phenylbenzohydroxamic Acid

Abstract

A rapid method for the simultaneous solvent extraction and spectrophotometric determination of macro-amounts of hexavalent uranium with N-phenyl-benzohydroxamic acid is described. The intense blood-red colored complex thus extracted from chloroform at pH ～ 4 absorbs at around 510 nm. A clean-cut separation from many commonly occurring metal ions is easily accomplished. Effects of acidity, reagent concentration, and diverse ions on the visible absorption of the extracted complex have also been investigated.     

Selective Extraction and Spectrophotometric Determination of Vanadium(V) with N-Hydroxy-N-p-chlorophenyl-N′-(2-methyl-5-chloro)phenyl-p-toluamidine Hydrochloride and Various Monobasic Carboxylic Acids

Abstract

N-Hydroxy-N-p-chlorophenyl-N′-(2-methyl-5-chloro)phenyl-p-toluamidine hydrochloride (HCPMCPTH), a newly synthesized bidentate chelating agent, reacts with vanadium(V) in the presence of monobasic carboxylic acids to give blue-violet water-insoluble adducts. The adducts have been extracted into various organic solvents such as chloroform, benzene, and carbon tetrachloride, and employed for the spectrophotometric determination of vanadium(V) and its separation from diverse ions. Investigations of the vanadium-HCPMCPTH-carboxylic acid complexes by spectrophotometric and solvent extraction techniques showed that the complex had the composition VO(OAm)₂OH.HOOCR (where HOAm = hydroxyamidine and HOOCR = carboxylic acid). The molar absorptivity and wavelength of maximum absorption of the mixed complex depend on the nature of the carboxylic acid used.     

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.     

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.     

Liquid-Liquid Phase Distribution Studies of Chromium(VI) between Mineral Acid Solutions and 5-(4-Pyridyl)nonane N-Oxide in Benzene,and Enrichment by Extraction Plant with Pulsation Column

Abstract

A liquid-liquid extraction system consisting of a benzene solution of 5-(4-pyridyl)nonane N-oxide (P_yNO_x) and mineral acid solutions has been studied for the extraction of chromium(VI). The optimal conditions for the extraction have been carefully selected from a critical study of the various factors involved, such as the effects of the concentration of the mineral acids, chromium, and the solvent; and the salting and complexing agents. Common anions have little effect on extraction in concentrations up to 0.5 M. Backextraction of the metal can be accomplished by a number of solutions and by water. Extraction of several metals was investigated under optimal conditions for the extraction of chromium. Common base metal ions like iron, aluminum, magnesium, calcium, etc. are not extracted. The mechanism of extraction has been studied by using slope analyses and saturation experiments. The predominant mode of extraction appears to be ionic association with the probable composition of the extracted species being P_yNO_xH⁺.HCr₂O₇ ^?, with some additional contribution by benzene. Extraction at a high aqueous to organic ratio has been studied by using an extraction plant with a pulsation column.     

The Influence of Extractant Structure on the Solvent Extraction of Uranium(VI) and Thorium(IV) from Nitrate Media by Dialkyl Sulphoxides

The solvent extraction of uranium(VI) and thorium(IV) from sodium nitrate solutions (0·20–6·00 M ) by a series of dialkyl sulphoxides with different structures was studied. For sulphoxides with n-alkyl groups (R₂SO, where R = n-hexyl, n-octyl and n-decyl) using 0·20 M solutions in xylene, the extractions of both uranium and thorium are relatively high, and the values of the separation factor β_Th^U are correspondingly low (≈20). Replacement of an n-hexyl group by a cyclohexyl group has little effect on metal extraction, whilst the introduction of a second cyclohexyl group causes a slight decrease in extraction. Similarly, there is little variation in the extraction of uranium and thorium through the series of asymmetrical compounds RR′SO, where R = n-octyl and R′ = cyclopentyl, cyclohexyl or cyclooctyl. When two aromatic (phenyl) rings are introduced into the sulphoxide, however, the extraction of both metals falls to zero. For the series of isomeric compounds R₂SO with C₈ alkyl groups, the separation factors increase in the order: R = n-octyl, 2-ethylhexyl, 2-octyl, 3-octyl, which is also the order of increasing steric bulk of the alkyl group. For these compounds, slope analysis studies are consistent with the formulation of the extracted metal complexes as UO₂(NO₃)₂(R₂SO)₂ and Th(NO₃)₄(R₂SO)₃. © 1997 SCI.     

Liquid-Liquid Extraction Studies of Trivalent Yttrium from Phosphoric Acid Solutions Using TOPS 99 as an Extractant

Liquid-liquid extraction studies of trivalent yttrium (Y) from phosphoric acid solutions have been carried out with commercial organophosphoric acid based extractant TOPS 99 (Talcher Organo phosphorus solvent, an equivalent of di-2-ethylhexyl phosphoric acid). The parameters studied include equilibration time, acid concentration, extractant concentration, diluent, metal concentration, temperature, stripping, and regeneration of the extractant. Increase of phosphoric acid concentration in the range from 0.01 to 0.5 M on the extraction of trivalent Y with 6 × 10^?3 M TOPS 99 (Talcher Organo phosphorus solvent) decreases the percentage extraction, indicating the transfer of metal follows ion exchange type reaction. The plot of log D vs. equilibrium pH gave a straight line with a slope of 3.1 indicating the exchange of three moles of hydrogen ions for every mole of trivalent Y extracted into the organic phase. Stripping of metal from the loaded organic with mineral acids indicate sulphuric acid as the best stripping agent. The extraction behavior of associated elements clearly follows their ionic radii with a maximum separation factor of 414 for Lu-Tb.     

Ethylammonium nitrate enhances the extraction of transition metal nitrates by tri-n-butyl phosphate (TBP)

Several molecular polar solvents have been used as solvents of the more polar phase in the solvent extraction (SX) of metals. However, the use of hydrophilic ionic liquids (ILs) as solvents has seldomly been explored for this application. Here, the hydrophilic IL ethylammonium nitrate (EAN), has been utilized as a polar solvent in SX of transition metal nitrates by tri-n-butyl phosphate (TBP). It was found that the extraction from EAN is considerably stronger than that from a range of molecular polar solvents. The main species of Co(II) and Fe(III) in EAN are likely [Co(NO₃)₄]²⁻ and [Fe(NO₃)₄]⁻, respectively. The extracted species are likely Fe(TBP)₃(NO₃)₃ and a mixture of Co(TBP)₂(NO₃)₂ and Co(TBP)₃(NO₃)₂. The addition of H₂O or LiCl to EAN reduces the extraction because the metal cations coordinate to water molecules and chloride ions stronger than to nitrate ions. This study highlights the potential of using hydrophilic ILs to enhance SX of metals.     

Studies on Thorium Phosphate Ion Exchanger. Part III. Paper Chromatographic Behavior and Separations of Metal Ions on Thorium Phosphate Papers

Abstract

Thorium phosphate papers have been prepared by treatment with thorium nitrate and phosphoric acid solutions. Several metal ions have been chromatographed on thorium phosphate paper. The effect of pH on R_F values has been investigated. Some useful analytical separations of metal ions have been achieved by using only dilute mineral acid and a mixed solvent system.     

Thiosubstituted Organophosphorus Acids as Selective Extractants for Ag(I) from Acidic Thiourea Solutions

Abstract

This paper deals with the solvent extraction of silver from thiourea leaching Ag ore liquors as an alternative to the traditional process involving cyanide. The investigation of the extraction mechanism of silver from acidic thiourea solution had not been clearly established to date.

The extraction behavior of silver using di(2‐ethylhexyl)dithiophosphoric acid (D2EHDTPA) and di(2,4,4‐trimethylpentyl) thiophosphinic acid (CYANEX 302) was studied. The effect of various parameters such as concentrations of metal, mineral acid, thiourea, and extractant has been investigated. The extracted complexes have been identified through a slope method analysis as AgX(HX)₅ for CYANEX 302 and AgX for D2EHDTPA, where HX denotes the extractant. Moreover, complete stripping was ensured with a mixture of NH₄SCN and H₂SO₄. In addition we showed that a first step of extraction with D2EHPA or CYANEX 272 results in the preferential separation of Fe(III) from the Ag(I) leach solution.     

Paper Chromatographic and Electrochromatographic Separation of EDTA Complexes of Metal lons

Abstract

R_F values of EDTA complexes of some common metal ions in seven solvent systems are given. The separation of Al and Be EDTA complexes has been achieved in different ratios by paper chromatography. Paper electrophoresis is also performed in four solvent systems to study the separation of EDTA complexes of metal ions.     

Combined Ion Exchange—Solvent Extraction (CIESE): A Novel Separation Technique for Inorganic Ions

Abstract

In the present paper a novel separation technique for inorganic ions is described. This has been termed combined ion exchange—solvent extraction (CIESE), because it is assumed that both ion exchange and solvent extraction are operative simultaneously to effect the separations. This concept is illustrated with two examples: the separation of iron(III), Co(II), and Ni(II) on the ion-exchange resins Dowex 50 and Dowex 1 using acetone or tetrahydrofuran—hydrochloric acid mixtures, and the separation of uranium from numerous metal ions on Dowex 50, employing as eluent a medium consisting of tetrahydrofuran—nitric acid. Because this separation principle is superior to methods employing the conventional separation techniques of ion exchange in pure aqueous solutions and of common liquid-liquid extraction, it is expected that it will also find application for the solution of other problems encountered in inorganic analytical chemistry.     

EXTRACTION AND SEPARATION OF ZIRCONIUM(IV) WITH 3-HYDROXY-2-METHYL-1-PHENYL-4-PYRIDONE

ABSTRACT The extraction of zirconium(IV) from aqueous hydrochloric, sulphuric and perchloric acid solutions with 3-hydroxy-2-methyl--1-phenyl-4-pyridone (HX) dissolved in chloroform is described. Perchlorate and thiocyanate ions show a synergistic effect on zirconium extraction with HX. The synergistic effect of thiocyanate is stronger than the effect of perchlorate.

The composition of the extracted zirconium(IV) complexes is studied and a simple and rapid method for the separation of zirconium from niobium is described.     

Solvent extraction separation of vanadium(V) from multivalent metal chloride solutions using 2‐ethylhexyl phosphonic acid mono‐2‐ethylhexyl ester

The solvent extraction behaviour of vanadium(V) from hydrochloric acid solutions has been investigated using 2‐ethylhexyl phosphonic acid mono‐2‐ethylhexyl ester (EHEHPA ≡ HX) in kerosene as an extractant. For comparison, extraction studies have also been carried out with vanadium(IV). The results demonstrate that the extraction of vanadium(V) follows the cation exchange mechanism: where (HX)₂ refers to the dimeric form of EHEHPA. On the other hand, two dimeric molecules of EHEHPA were found to be involved in the extracted complex of vanadium(IV): The equilibrium constants of the above extracted complexes have been calculated and found to be K_ex,V(V) = 3.14 and K_ex,V(IV) = 0.32. The effect of the nature of the diluent on the extraction of vanadium(V) with EHEHPA has been studied and correlated with the dielectric constants. IR spectral studies of the extracted complex were used to further clarify the nature of the extracted complex. The separation and recovery possibilities of vanadium(V) from other associated metal ions, viz magnesium(II), aluminium(III), titanium(IV), chromium(III), manganese(II) and iron(III), which are present in the waste chloride liquors from the processing of titanium minerals, are also discussed. © 2002 Society of Chemical Industry     

Extraction of Lanthanides(III) and Am(III) by Mixtures of Malonamide and Dialkylphosphoric Acid

Abstract

N,N′‐dimethyl‐N,N′‐dioctylhexylethoxymalonamide, DMDOHEMA, and di‐n‐hexylphosphoric acid, HDHP, are the extractants of reference for the French DIAMEX–SANEX process for the separation of trivalent actinide ions from the lanthanide ions. In this work, the extraction of Eu³⁺ and Am³⁺ by the two extractants, alone or in mixtures, has been investigated under a variety of experimental conditions. The two cations are extracted by HDHP as the M(DHP · HDHP)₃ complexes with an Eu/Am separation factor of ～10. With DMDOHEMA, Eu³⁺ and Am³⁺ are extracted as the M(NO₃)₃(DMDOHEMA)₂ disolvate species with an Am/Eu separation factor of ～2. The metal distribution ratios measured with a mixture of the two reagents indicated that almost all lanthanides are extracted equally well. The extraction of Eu³⁺ and Am³⁺ by HDHP‐DMDOHEMA mixtures exhibits a change of extraction mechanism and a reversal of selectivity taking place at ～1 M HNO₃ in the aqueous phase. Below this aqueous acidity, HDHP dominates the metal extraction by the mixture, whereas DMDOHEMA is the predominant extractant at higher aqueous acidities. Some measurements indicated apparent modest antagonism between the two extractants in the extraction of Eu³⁺ and synergism in the extraction of Am³⁺. These data were interpreted as resulting from the formation in the organic phase of mixed HDHP‐DMDOHEMA species containing two HDHP and five DMDOHEMA molecules.     

Extraction of some Hexavalent Actinide Ions from Nitric Acid Medium using Several Substituted Diglycolamides

Several substituted diglycolamides, namely TPDGA, THDGA, TODGA, and TDDGA, were evaluated in a comparative study on the extraction of hexavalent actinide ions such as UO₂²⁺, NpO₂²⁺, and PuO₂²⁺ from nitric acid medium. The acid extraction constants (K_H) for the diglycolamides were determined to be 3.8 ± 0.6, 1.6 ± 0.1, 4.1 ± 0.4, and 1.4 ± 0.2 for TPDGA, THDGA, TODGA, and TDDGA, respectively. Though metal ion extraction generally increased with increasing the feed acid concentration, the nature of the extracted species changed with aqueous-phase acidity. While complexes of the type MO₂(NO₃)₂·nL (where L is the diglycolamide extractant and n is 1 and 2) were found to be extracted at 1 M HNO₃, the average number of ligand molecules associated with the complex decreased to ?1 when the nitric acid concentration increased to 3 M. These results have great significance from the actinide separation point of view, as the actinides ions can be made virtually inextractable by adjusting their oxidation state. The thermodynamic parameters were also calculated, which indicated spontaneous reactions with large exothermicities.     

NITROGEN REAGENTS IN METAL ION SEPARATION. PART IX. EXTRACTION OF COBALT AND NICKEL USING IMIDAZOLE DERIVATIVES

ABSTRACT

The extraction capability of derivatives of imidazole towards Co(II) and Ni(II) has been investigated in dilute acid medium in the presence of each of chloride, perchlorate and thiocyanate ions. The influence of the stereochemistry of the substituted imidazole on the extraction behaviour has been investigated. Two-phase potentiometric titrations were employed to determine the nature of the metal species extracted into the organic phases. The electronic spectra of the extracted metal species have been employed to provide information of the nature of such species.     

The Partitioning of Americium and the Lanthanides Using Tetrabutyldiglycolamide (TBDGA) in Octanol and in Ionic Liquid Solution

Separations among the lanthanides and the separation of Am from the lanthanides remain challenging, and research in this area continues to expand. The separation of adjacent lanthanides is of interest to high-tech industries because individual lanthanides have specialized uses and are in short supply. In nuclear fuel cycle applications Am would be incorporated into fast-reactor fuels, yet the lanthanides are not desired. In this work, the diglycolamide N,N,N′,N′-tetrabutyldiglycolamide (TBDGA) was investigated as a ligand for lanthanide and Am solvent extraction in both molecular and room-temperature-ionic-liquid (RTIL) diluents.The RTIL [C₄MIM][Tf₂N] showed very high extraction efficiency for these trivalent metals from low nitric acid concentrations, while the molecular diluent 1-octanol showed high extraction efficiency at high acid concentrations. This was attributed to the extraction of ionic nitrate complexes by the RTIL, whereas 1-octanol extracted neutral nitrate complexes. TBDGA in RTIL did not provide adequate separation factors for Am/lanthanide partitioning, but 1-octanol did show reasonable separation possibilities. Lanthanide intergroup separations appeared to be feasible in both diluents, but with higher separation factors from 1-octanol.