Evaluation of Novel Solvent Systems Containing Calix-crown-6 Ligands in A Fluorinated Solvent for Cesium Extraction from Nitric Acidic Feeds

Several commercial calix-crown-6 ligands such as: calix[4]arene-bis-crown-6 (CC), calix[4]arene-bis-benzo-crown-6 (CBC), calix[4]arene-bis-naphtho-crown-6 (CNC), and bis-(octyloxy)calix[4]arene-mono-crown-6 (CMC) have been evaluated for their Cs uptake ability from nitric acid feed solutions in a novel solvent system. The calix-crown-6 ligands were made soluble in phenyl trifluoromethyl sulphone (PTMS) and 1 × 10^?3 M solutions were used for metal ion extraction from nitric acid feed solutions. The extraction efficiency of the calix-crown-6 ligands was found out to be: CBC > CNC > CMC ? CC, which was attributed to trends of their partition coefficients. CNC was considered to be the most suitable extractant in view of its better organophilicity. The effects of concentrations of nitric acid and Cs carrier in feed were also investigated. Studies carried out using variation of ligand concentration yielded an extracted species of the type [CsL⁺][NO₃^?]_org. Stripping of Cs(I) from the loaded organic phase was found to be possible when the organic phase contained minute quantities of Alamine 336. Co-current extraction and stripping studies were also carried out using CNC as the extractant.     

Investigation into Coordination States of Diglycolamide and Dioxaoctanediamide Complexes with Lanthanide Elements Using Spectroscopic Methods

The extraction behavior and complexation state of diglycolamide (DGA) and dioxaoctanediamide (DOODA) ligands were investigated for several trivalent lanthanide ions (Ln(III)). The stoichiometry of the extraction of La(III), Nd(III), and Ho(III) with the hydrophobic ligands, N,N,N’,N’-tetraoctyl diglycolamide (TODGA) and N,N,N’,N’-tetraoctyl dioxaoctanediamide (DOODA(C8)), was determined by slope analyses in CHCl₃ and CCl₄ system. Ultraviolet-visible (UV-Vis) spectroscopy was employed for determination of the stability constants (β) of trivalent lanthanide ion (Ln³⁺) with the hydrophilic ligands, N,N,N’,N’-tetraethyl diglycolamide (TEDGA) and N,N,N’,N’-tetraethyl dioxaoctanediamide (DOODA(C2)). DGA ligands are found to have an affinity of heavier Ln(III), while DOODA ligands prefer to coordinate with lighter Ln(III). Infrared (IR) and nuclear magnetic resonance (NMR) spectroscopic measurements reveal that the carbonyl oxygen atoms of TODGA and DOODA(C8) worked as dominant donors in complexation with La(III). In contrast, the ether oxygen of the hydrophilic ligands makes major contribution to formation of La(III) complex.     

Regeneration of Mixed Solvent by Ion Exchange Resin: Selective Removal of Chloride and Sulfate

Abstract

The selective extraction of sulfate and chloride ions from mixed solvent solutions was investigated. The mixed solvents consisted of water and 50 to 100%‐w (salt‐free solvent) ethylene glycol. The extraction was measured for mixed solvent solutions containing only sulfate and chloride, and mixed solvent solutions saturated with trona (sodium sesquicarbonate, Na₂CO₃ · NaHCO₃ · 2H₂O(s). Three anion exchange resins, Dowex 1X8‐50, Dowex 21K‐Cl, and Dowex MSA‐1, were investigated for their chemical and physical resistance to the mixed solvent carbonate/bicarbonate solutions, for their swelling behavior in the different mixed solvents, and for their extraction efficiency for chloride and sulfate.

The loading of the ion exchangers was fitted to a Langmuir‐type sorption model. While the extraction from trona‐free mixed solvents was well reproduced, the loading of the ion exchangers with chloride and sulfate from trona‐saturated mixed solvent solutions did not fit the sorption model. It appears, rather, that under these conditions chloride and sulfate are “salted out” of the bulk solution and driven into the ion exchangers.     

Extraction behaviour of dioxouranium(VI) cation by two phosphorous-based liquid cation-exchangers in room-temperature ionic liquids

Extraction of uranium with bis-(2-ethylhexyl) phosphonic acid (PC-88A) and bis(2,4,4-trimethylpentyl) phosphinic acid (Cyanex-272) was studied in several imidazolium-based room-temperature ionic liquids (RTILs), C_nmim·X (where n = 4, 6, 8 and X = PF₆ and Tf₂N). The extraction kinetics was slow and about 0.5–1 h equilibration time was required for most of the extraction systems, except in C₈mim·PF₆, where 2 h and 4 h were required to reach the equilibrium values for PC-88A and Cyanex-272, respectively. The extraction of UO₂²⁺ ion by the two ligands was significantly affected by the nature and the composition of the RTILs.     

Strong and Selective Ni(II) Extractants Based on Synergistic Mixtures of Sulfonic Acids and Bidentate N-Heterocycles

ABSTRACT

Bidentate 5,5?-alkyl-3,3?-bi-1H-pyrazole and 2-(5-alkyl-1H-pyrazol-3-yl)pyridine ligands, L⁵ and L⁶, have been shown to be stronger synergists for the solvent extraction of Ni(II) from sulfate solutions by dinonylnaphthalene sulfonic acid (DNNSAH) than the structurally related tridentate ligand 2,6-bis-[5-n-nonylpyrazol-3-yl]pyridine, L¹, previously reported by Zhou and Pesic. The bidentate ligands are highly selective, providing the option of sequential recovery of Ni(II) and Co(II) and rejection of other metals commonly found in the liquors resulting from the acidic sulfate leaching of laterite ores. They were the strongest synergists identified in a screening carried out on 18 types of bidentate and tridentate N-heterocyclic ligands, including the recently reported 2-(2?-pyridyl)imidazoles, L^9?11. X-ray crystal structures of Ni(II) complexes of model ligands for L⁵ and L⁶, having t-butyl rather than long-chain alkyl groups and with 2-naphthalene sulfonate rather than DNNSA^? as counteranions, show that the [Ni(L)₃]²⁺ complexes form strong H-bonds from the pyrazolyl NH groups to the oxygen atoms of the sulfonate groups, an arrangement that will stabilize [Ni(L)₃·(DNNSA)₂] assemblies and shield their polar functionalities from diluent molecules of the water-immiscible phase. UV–visible spectra and mass spectrometry provide evidence for the strong synergists displacing all water molecules from the inner coordination sphere of the Ni(II) ions.     

Solvent Extraction of Uranium (VI) from Chloride Solutions using Cyphos IL-101

The solvent extraction of uranium (VI) from chloride solutions by Cyphos IL-101 in xylene has been studied. Distribution coefficients were found to increase with aqueous chloride concentration and extractant concentration. The enthalpy of extraction is endothermic with ΔH = +24 ± 2 kJ·mol^?1. Based upon slope analysis, an anion exchange extraction mechanism is proposed, with formation of a UO₂Cl₄ ^2- complex in association with 4 Cyphos IL-101 ligands. The extraction kinetics were fast, with complete equilibration occurring within 30 seconds. An isotherm for uranium extraction from 1.0 mol·L^?1 chloride solution by 0.1 mol·L^?1 Cyphos IL-101 in xylene shows that 45 mmol·L^?1 uranium can be loaded into the organic phase in equilibrium with 2.1 mmol·L^?1 in the aqueous phase. The absorption spectrum of the uranium loaded solvent between 350 and 550 nm is indicative of the UO₂Cl₄ ^2- complex with only chlorides present in the inner coordination sphere, unlike the more strongly hydrogen bonded Alamine 336 extracted uranium complex. Subject to the same experimental conditions, distribution coefficients for Cyphos IL-101 were significantly greater than for Alamine 336 or Aliquat 336.     

EXTRACTION OF PLUTONIUM BY CHELATING HYDROXYPYRIDINONE AND CATECHOLAMIDE RESINS∗

ABSTRACT

Four new chelating hydroxypyridinone and catecholamide polystyrene-supported extractants have been prepared and evaluated for their ability to selectively remove ppm levels of plutonium from a variety of acidic aqueous waste compositions. The hydroxypyridinone and catecholamide ligands, modeled after the metal ion binding sites found in siderophores, were derivatized to allow covalent attachment to a polymeric support. The synthesis, loading capacities and chemical stability of the new resins are reported along with the results from extraction studies evaluating their performance for the extraction of Pu(IV) and Pu(VI) from a variety of HNO₃ and NaN0₃ solutions up to 5 M and in competition with Fe(III), Al(III), Zr(IV) and EDTA. The kinetics of metal ion sorption onto the resins are fast, and the extraction results are compared to the commercial Chelex resin.     

SOLVENT EXTRACTION OF MOLYBDENUM (VI) WITH LIX 63

The equilibrium and kinetics of the extraction of molybde-num(VI) with LIX 63 was investigated. The extraction of Mo(VI) is both favored by high acidity and high LIX 63 concentration. From the equilibrium studies, the extraction constant for the reaction was found to be log K_ex - 16.43. The rate of extraction is first ex order in both metal and extractant but decreases non-linearly with pH. The rate-determining step of the reaction was deduced to be the formation of a 1:1 complex between Mo(VI) and LIX 63 in the aqueous phase. A mechanism in which different Mo(VI) species react concurrently with the neutral ligand is proposed. The logarithmic values of the second order reaction rate constants (in M^?1 s^?1 units) involving each Mo(VI) species are as follows: molybdate - 2.30, bimolybdate - 5.82, and molybdic acid - 8.16. These results agree well with the results reported for other ligands.     

The Influence of the Hofmeister Bias and the Stability and Speciation of Chloridolanthanates on Their Extraction from Chloride Media

The possibility of recovering rare earth elements from solutions containing their chloridometalate anions [LnCl_x]^(x?3)? via the process: LnCl_x^(x?3)? + (x ? 3)L_org + (x–3)H⁺ ? [(LH)_x?3LnCl_x]_org has been tested using 2-(1,3-bis(hexylamino)-1,3-dioxopropan-2-yl)-4,6-di-tert-butylpyridine (PMA), tri-n-butylphosphate (TBP), and tri-n-octylamine (TOA), which are known to be strong extractants for transition metal chloridometalates. While DFT calculations indicate that the formation of the neutral assembly [(PMAH)₃LaCl₆] in the gas phase is favorable, no uptake of La(III) from 6 M HCl by toluene solutions of PMA (or of TBP or TOA) was observed in solvent extraction experiments. Successful uptake of the [PtCl₆]^2? dianion by PMA and the failure to extract the [IrCl₆]^3? trianion under the same conditions indicate that the higher hydration energy of the latter makes transfer to the toluene solution less favorable and that this militates against extraction of La(III) chlorido complexes carrying charges of ?3 or larger in which all the inner-sphere water molecules have been replaced. Computational results confirm literature observations that, in contrast to transition metal trications, formation of REE metalate anions such as [LnCl_x]^(x?3)? is not very favorable, particularly so for chloride, compared with nitrato or sulfato systems. Also, they indicate that the formation of outer-sphere assemblies such as {[La(H₂O)₉]·xCl} in which water ligands are retained in the inner sphere, H-bonded to anions, is more stable than inner-sphere complexes containing an equivalent number of anions. The high level of hydration of such species disfavors their transfer into nonpolar water-immiscible solvents. It is unlikely that recovery of [LnCl_x]^(x?3)? from acidic solutions can be achieved efficiently using currently available anion exchange extractants operating in a “pH-swing” process. Receptors giving very high binding energies to chloridolanthanates will be needed to offset the high dehydration energies required.     

Evaluation of Mononuclear Ni(II) Complex of a Tetra-cryptanded Vic-dioxime and its Model Compound 14-Membered N2O2S2-Macrobicyclic Ligand as Pb2+, Cd2+, and Hg2+ Extractants

Abstract

A macrobicyclic ligand and its mononuclear Ni(II) complex were studied as extractants for Pb²⁺, Cd²⁺, and Hg²⁺. The metal picrates were used for extraction experiments. The solutions of the ligands in chloroform and dichloromethane were used as organic phases. The most effective transport was observed for Cd²⁺ picrate among the tested metal picrates with dichloromethane. The effect of pH on the extraction efficiency was evaluated for both organic solvents. The cations were stripped from the organic phase with 0.75 M nitric acid and the ligands were determined spectrophotometrically in the proper wavelength. The recovery% values of the ligands were calculated at pH 3.5.     

The Synthesis and Characterization of New Schiff Bases and Investigating them in Solvent Extraction of Chromium and Copper

New Schiff bases containing nitrogen, sulfur and oxygen donor atoms, were designed and synthesized in a multi—step reaction sequence. The Schiff base(I) was used in solvent extraction of metal chlorides such as Cu(II) from aqueous phase to the organic phase. The influences of the parameter functions, such as pH, solvent, ionic strength of aqueous phase, aqueous to organic phase, and concentration of the extractant were investigated to shed light on their chemical extracting properties upon the extractability of metal ions. The effect of chloroform, dichloromethane, and nitrobenzene as organic solvents over the metal chlorides extraction was investigated at 25 ± 0.1°C by using flame atomic absorption and the result is that the ability of extraction in solvents as follows C₆H₅NO₂ > CHCl₃ > CH₂Cl₂.     

Evaluation of a (E,E)‐Dioxime Containing Two 15‐Membered Dioxatrithiamacrocycles and its Mononuclear Ni(II) Complex as Ag+ Extractants

Abstract

A macrocyclic vic‐dioxime (1) and its mononuclear Ni(II) complex (2) were studied as extractant. The aqueous solutions of Ag⁺, Mn²⁺, Pb²⁺, Ni²⁺, Cu²⁺, Cd²⁺, and Zn²⁺ picrates were used for extraction experiments. The solutions of the ligands in two different organic solvents were used as organic phases. The metal picrate extractions were carried out at 25±0.1°C by using UV‐visible spectrometry. The most effective transport was observed for Ag⁺ picrate among the tested metal picrates. The effect of pH on the extraction of Ag⁺ picrate was evaluated with the ligands. The ratio of extracted Ag‐complex to chloroform phase was 2:1 (L:M) for (2). In other cases the ratios were 1:1 for both (1) and (2). Molar ratio method was also used to demonstrate the composition. The values of the extraction constants (log K_ex) were determined for the extracted Ag‐complexes.     

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

ABSTRACT

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

Mechanistic study of hafnium and zirconium extraction with organophosphorus extractants

Research on the purification of Zr has increased in the last few decades and although effective processes have been developed, little is known about the mechanism of Hf and Zr extraction; particularly, at low acid concentrations. This study’s aim was to determine the influence of alterations in alkyl substituents on the extraction mechanism of Hf and Zr from sulfate media. Seven organophosphorus extractants (Dio-PA, TPPA, DPPA, TPPO, TPPS, D2EHPA and Ionquest 801) were screened with four of them (Dio-PA, DPPA, D2EHPA and Ionquest 801) resulting in promising extraction results. This was attributed to the activity of the acidic hydroxy phosphinyl (=P(O)OH) group which is responsible for the dimerization and cation exchange properties of the extractant. The extractant and hydrogen ion stoichiometries involved in the extraction mechanism were determined for these four extractants by slope analysis from extractant- and acid-variation experiments. It was found that Dio-PA, D2EHPA, and Ionquest 801 extract via a cation-exchange mechanism, according to [M(OH)₂]²⁺ + 2 HA ? M(OH)₂A₂ + 2 H⁺. In contrast, the extraction with DPPA was best described by a solvated cation exchange (SCE) mechanism, according to [M(OH)]³⁺ + 6 HA ? M(OH)A₃.3HA + 3 H⁺. It was concluded that the presence of electron-withdrawing substituents produced softer Lewis base extractants, which favored the extraction of Hf over Zr from acidic sulfate media.     

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.     

Supercritical Carbon Dioxide Extraction of Carotenoids from Pumpkin (Cucurbita spp.): A Review

Carotenoids are well known for their nutritional properties and health promoting effects representing attractive ingredients to develop innovative functional foods, nutraceutical and pharmaceutical preparations. Pumpkin (Cucurbita spp.) flesh has an intense yellow/orange color owing to the high level of carotenoids, mainly α-carotene, β-carotene, β-cryptoxanthin, lutein and zeaxanthin. There is considerable interest in extracting carotenoids and other bioactives from pumpkin flesh. Extraction procedures able to preserve nutritional and pharmacological properties of carotenoids are essential. Conventional extraction methods, such as organic solvent extraction (CSE), have been used to extract carotenoids from plant material for a long time. In recent years, supercritical carbon dioxide (SC-CO₂) extraction has received a great deal of attention because it is a green technology suitable for the extraction of lipophylic molecules and is able to give extracts of high quality and totally free from potentially toxic chemical solvents. Here, we review the results obtained so far on SC-CO₂ extraction efficiency and quali-quantitative composition of carotenoids from pumpkin flesh. In particular, we consider the effects of (1) dehydration pre-treatments; (2) extraction parameters (temperature and pressure); the use of water, ethanol and olive oil singularly or in combination as entrainers or pumpkin seeds as co-matrix.     

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.     

Ionic Liquid (IL) Cation and Anion Structural Effects on Metal Ion Extraction into Quaternary Ammonium-based ILs

Numerous factors have previously been shown to influence the mode of extraction of alkali and alkaline earth cations from an acidic aqueous phase into 1, 3-dialkylimidazolium-based ionic liquids (ILs) by a crown ether, among them the hydrophobicity of both the IL anion and cation. To determine if this observation is “generic” and thus, could provide the basis for guidelines for the rational design of ILs to be used as solvents in metal ion extraction, other families of ILs must be studied. A series of quaternary ammonium-based ILs have therefore been examined as solvents for the extraction of various metal ions from acidic nitrate- and chloride-containing aqueous phases by dicyclohexano-18-crown-6 (DCH18C6). Although the overall metal ion extraction behavior in these systems is similar to that observed for 1, 3-dialkylimidazolium-based ILs, significant differences in metal ion separation factors (e.g., α_Sr/Na) are observed under certain conditions, differences that may be sufficient to influence the choice of IL in separations applications.     

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.     

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.