6,6′‐Bis(5,5,8,8‐tetramethyl‐5,6,7,8‐tetrahydro‐benzo[1,2,4]triazin‐3‐yl) [2,2′]bipyridine,an Effective Extracting Agent for the Separation of Americium(III) and Curium(III) from the Lanthanides

Abstract

The extraction of americium(III), curium(III), and the lanthanides(III) from nitric acid by 6,6′‐bis(5,5,8,8‐tetramethyl‐5,6,7,8‐tetrahydro‐benzo[1,2,4]triazin‐3‐yl)‐[2,2′]bipyridine (CyMe₄‐BTBP) has been studied. Since the extraction kinetics were slow, N,N′‐dimethyl‐N,N′‐dioctyl‐2‐(2‐hexyloxy‐ethyl)malonamide (DMDOHEMA) was added as a phase transfer reagent. With a mixture of 0.01 M CyMe₄‐BTBP+0.25 M DMDOHEMA in n‐octanol, extraction equilibrium was reached within 5 min of mixing. At a nitric acid concentration of 1 M, an americium(III) distribution ratio of approx. 10 was achieved. Americium(III)/lanthanide(III) separation factors between 50 (dysprosium) and 1500 (lanthanum) were obtained. Whereas americium(III) and curium(III) were extracted as disolvates, the stoichiometries of the lanthanide(III) complexes were not identified unambiguously, owing to the presence of DMDOHEMA. In the absence of DMDOHEMA, both americium(III) and europium(III) were extracted as disolvates. Back‐extraction with 0.1 M nitric acid was thermodynamically possible but rather slow. Using a buffered glycolate solution of pH=4, an americium(III) distribution ratio of 0.01 was obtained within 5 min of mixing. There was no evidence of degradation of the extractant, for example, the extraction performance of CyMe₄‐BTBP during hydrolylsis with 1 M nitric acid did not change over a two month contact.     

Solvent Penetration and Sterical Stabilization of Reverse Aggregates based on the DIAMEX Process Extracting Molecules: Consequences for the Third Phase Formation

Abstract

Studies on third phase formation during the extraction of nitric acid by malonamide extractants in various diluents are investigated. This “third phase transition” is studied from a fundamental point of view, combining vapor pressure osmometry, phase diagram, and scattering studies. The organization of the organic phases of the “malonamides/alkane/water/nitric acid” systems was studied at three “scales”: 1/at a molecular scale by determining the compositions of the extracted complexes; 2/at a macroscopic scale by determining the phase transition boundaries quantified by the limiting organic concentration (LOC) of solutes; and 3/at a supramolecular scale by analyzing the organization of the species in the organic phases (i.e. measuring the critical micellization concentration, the aggregation number, and the interactions between the aggregates). The instability (third phase apparition) has a supramolecular origin: it is a “long range” attraction between polar cores of the reverse micelles formed by the extracting agent. Water and nitric acid extraction are decoupled from these interactions. The alkyl chains of the extractant and the diluent play a symmetrical role in the physical stability of the organic phase: decreasing the diluent chain length or increasing the chain length of the complexing agent both promotes phase stability, i.e. they increase the LOC. We demonstrate here that this effect is the same as the effect observed and known for all other w/o “reverse” micelles: chains protruding from any aggregate stabilize polar solute in oil and shorts oil penetrate and swells the reverse micelles apolar layer.     

Aggregation in Solvent Extraction Systems Containing a Malonamide,a Dialkylphosphoric Acid and their Mixtures

Abstract

Aggregation phenomena in n-alkane solutions of di-n-hexylphosphoric acid (HDHP), N,N′-dimethyl-N,N′-dioctylhexylethoxymalonamide (DMDOHEMA), and their mixtures, were investigated by electrospray ionization–mass spectrometry (ESI-MS), vapor pressure osmometry (VPO), and small-angle X-ray and neutron scattering (SAXS and SANS). The objective of the study was to probe the formation of mixed HDHP-DMDOHEMA species before and after extraction of trivalent lanthanide and actinide (M³⁺) nitrates. The most important species formed by HDHP upon metal extraction has the composition M(DHP)₃(HDHP)₃(H₂O). These species exist as spherical aggregates of the reverse micelle type with a polar core diameter of ～ 7 Å and total diameter of ～ 11 to ～ 15 Å. The aggregation of DMDOHEMA is a progressive phenomenon, with an average aggregation number of ～ 2 in the 0.2 to 0.6 M range and larger aggregates forming at higher concentrations. The metal loaded DMDOHEMA aggregates can be considered as interacting spheres with a polar core diameter between ～ 11 and ～ 16 Å, depending on composition, a total diameter of up to ～ 25 Å, and a weight-average aggregation number of ～ 9. The results obtained in this work provide strong evidence for the formation of mixed aggregates when mixtures of HDHP and DMDOHEMA are used for the extraction of trivalent Ln and An cations. These mixed reverse micelles have a diameter between 19 and 24 Å with a polar core diameter of 10 and to 14 Å. The most recurrent micellar composition is 2 HDHP and either 4 or 5 DMDOHEMA molecules.     

Palladium Extraction by a Malonamide Derivative (DMDOHEMA) from Nitrate Media: Extraction Behavior and Third Phase Characterization

Liquid-liquid extraction of palladium(II) from nitric media was carried out using, N,N’–dimethyl,N,N’-dioctylhexylethoxymalonamide (DMDOHEMA) in n-heptane. To this purpose, various experimental parameters such as reaction time, extractant concentration, pH, and nitrate concentration were investigated in detail. Efficient extraction of palladium can then be achieved, with good distribution coefficients (D up to 10) and performing kinetics (equilibration time ca. 30 min). In some cases, a solid phase appears at the interface between aqueous and organic layers. It was characterized as a palladium(II) complex with DMDOHEMA with appropriate techniques, and the conditions of its formation are discussed.     

Influence of Extractant Aggregation on the Extraction of Trivalent f‐Element Cations by a Tetraalkyldiglycolamide

Abstract

The influence of nitric acid extraction on the aggregation state of 0.10 M N,N,N′,N′‐tetra‐n‐octyl‐3‐oxapentane‐1,5‐diamide (TODGA) in n‐octane or n‐heptane was studied by small‐angle neutron scattering (SANS) and vapor pressure osmometry (VPO). When the equilibrium concentration of nitric acid in the aqueous phase is less than 0.7 M, TODGA exists as a mixture of monomers and dimers. As the aqueous phase acidity is increased, the extractant molecules form higher aggregates containing up to an average of seven molecules of TODGA. The formation of the larger TODGA aggregates takes place over the same range of aqueous acidities where the extraction of trivalent f‐element cations displays a hyperstoichiometric sixth power nitric acid dependence. This suggests that acid‐driven aggregation of TODGA is responsible for the unusual acid and extractant dependencies observed for the extraction of trivalent metal nitrates with this ligand.     

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.     

Comparison in the extraction behavior of uranium(VI) from nitric acid medium using CHON based extractants,monoamide, malonamide,and diglycolamide,dissolved in piperidinium ionic liquid

Liquid-liquid extraction of U(VI) from nitric acid medium was carried out using three different class of CHON based molecular extractants namely monoamide, malonamide, and diglycolamide present in 1-butyl-1-methylpiperidinium bis(trifluoromethanesulfonyl)imide ([C₄mpip][NTf₂]) ionic liquid. The extractants investigated were di-n-hexyloctanamide (DHOA), N,N-dimethyl-N,N-di-octyl-2-(2-hexyloxylethyl)malonamide (DMDOHEMA) and N,N,N’,N’-tetra(ethylhexyl)diglycolamides (T2EHDGA). The extraction behavior of uranium(VI) in ionic liquid medium was investigated as a function of various parameters, such as the duration and temperature of equilibration, aqueous phase concentrations of feed acid, extractant, NaNO₃, and ionic liquid cation, etc. The extraction of U(VI) observed in these systems were compared with each other and the distribution ratios of U(VI) decreased in the order T2EHDGA > DMDOHEMA > DHOA. The slope analysis of the extraction data was carried out to understand the mechanistic aspects of extraction. The extraction of U(VI) observed in [C₄mpip][NTf₂] ionic liquid was also compared with pyrrolidinium ([C₄mpyr][NTf₂]) and imidazolium ([C₄mim][NTf₂]) based ionic liquids under identical experimental condition.     

DIAMEX Counter‐Current Extraction Process for Recovery of Trivalent Actinides from Simulated High Active Concentrate

Abstract

The partitioning of trivalent actinides was demonstrated with a new version of the French DIAMEX (DIAMide EXtraction) process. A continuous counter‐current experiment using a 16‐stage centrifugal extractor battery was tested using 1 mol/L N,N′-dimethyl‐N,N′-dioctyl‐hexylethoxy‐malonamide (DMDOHEMA) in TPH as the extractant. A high active concentrate (HAC), obtained after concentration and denitration of a high active raffinate (HAR) with a concentration factor of 10, was used as a feed. Based on results from cold and hot batch extraction experiments and computer code calculations, a flowsheet was developed and a full test was carried out using a simulated HAC solution spiked with radionuclides (²⁴¹Am, ²⁴⁴Cm, ¹⁵²Eu, and ¹³⁴Cs). In the DIAMEX process, five extraction stages were sufficient to obtain Am and Cm (feed/raffinate) greater than 5000 and for the coextracted lanthanides decontamination factors between 1100 and 4500. Co‐extraction of zirconium, molybdenum, and palladium was prevented by using oxalic acid and HEDTA. The back extraction comprising 4 stages was also efficient and the recoveries of actinides were greater than 99.8%, which can be further improved by a minor process flowsheet optimisation. The experimental steady‐state concentration profiles of important solutes were determined and compared with model calculations and good agreement was generally obtained.     

Extraction Selectivity of a Quaternary Alkylammonium Salt for Trivalent Actinides over Trivalent Lanthanides: Does Extractant Aggregation Play a Role?

The extraction behavior of a quaternary alkylammonium salt extractant was investigated for its selectivity for trivalent actinides over trivalent lanthanides in nitrate and thiocyanate media. The selectivity was evaluated by solvent extraction experiments through radiochemical analysis of ²⁴¹Am and ^152/154Eu. Solvent extraction distribution and slope-analysis experiments were performed with americium(III) and europium(III) with respect to the ligand (nitrate and thiocyanate), extractant, and metal (europium only) concentrations. Further evaluation of the equilibrium expression that governs the extraction process indicated the appropriate use of the saturation method for estimation of the aggregation state of quaternary ammonium extractants in the organic phase. From the saturation method, we observed an average aggregation number of 5.4 ± 0.8 and 8.5 ± 0.9 monomers/aggregate for nitrate and thiocyanate, respectively. Through a side-by-side comparison of the nitrate and thiocyanate forms, we discuss the potential role of the aggregation in the increased selectivity for trivalent actinides over trivalent lanthanides in thiocyanate media.     

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

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

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

Behavior of Molybdenum (VI) in {DMDOHEMA–HDEHP/nitric acid} Liquid–Liquid Extraction Systems

The EXAm (extraction of americium) process was developed for americium recycling in future nuclear fuel cycles. In this solvent extraction system, a combination of two extractants, N,N′-dimethyl-N,N′-dioctyl-hexylethoxy malonamide (DMDOHEMA) and di-2-ethylhexyl phosphoric acid (HDEHP), in TPH (hydrogenated tetrapropylene) is used to extract americium in the first step of the process at high acidity (HNO₃ 5–6 M). Americium is co-extracted with light lanthanides and other fission products like molybdenum, iron, ruthenium, etc.. Molybdenum is selectively scrubbed during the second step at low acidity using citric or glycolic acid as a buffer and complexing agent. The speciation of Mo(VI) in aqueous solutions is highly dependent on acidity and Mo concentration. In this article, a simple thermodynamical model is proposed for Mo(VI) scrubbing based on batch extraction experiments (with pH and cation concentration variations) and stoichiometries of complexes formed in the organic phase according to electrospray ionization mass spectrometry (ESI-MS) experiments and published data on Mo(VI) speciation. At high acidity ([HNO₃] > 1 M), the MoO₂²⁺ species is strongly extracted by the solvent DMDOHEMA–HDEHP according to a solvate mechanism. At lower acidity ([HNO₃] < 1 M), cation exchange mechanisms become predominant and DMDOHEMA does not participate to the extraction Mo(VI) anymore. During Mo scrubbing at pH higher than 1, the extraction of Mo as neutral species (like MoO₃) and anionic species (like MoO₄^2–) has to be taken into account in the model to predict the “bell-shape” of Mo distribution ratio evolution as a function of pH. This model was then implemented in the PAREX simulation code developed by the CEA to build the flowsheet for the “Mo scrubbing” section of EXAm process and predict Mo concentrations profiles in batteries of mixer-settlers during pilot-scale tests.     

Liquid–liquid extraction of Hg(II) from acidic chloride solutions using bis‐2‐ethylhexyl sulfoxide

The liquid–liquid extraction of Hg(II) from acidic chloride solutions has been studied using bis‐2‐ethylhexyl sulfoxide (B2EHSO) as an extractant. For comparison, extraction studies have also been carried out using di‐n‐octyl sulfoxide (DOSO) and diphenyl sulfoxide (DPhSO). The extraction data have been analysed by both graphical and theoretical methods taking into account aqueous phase speciation and all plausible complexes extracted into the organic phase. These results demonstrate that Hg(II) is extracted into xylene as HgCl₂.3R₂SO (where R₂SO represents the sulfoxide). The equilibrium constant of the extracted complex has been deduced by non‐linear regression analysis. The developed liquid–liquid extraction procedure has been applied for the recovery of mercury from the brine‐sludge of a Chlor‐Alkali plant. © 2001 Society of Chemical Industry     

New Bitopic Ligands for the Group Actinide Separation by Solvent Extraction

Abstract

The synthesis and evaluation of solvent extraction performance of N,N,N′,N′-tetraalkyl-6,6″-(2,2′:6′,2″-terpyridine)diamides and N,N′-diethyl-N,N′-diphenyl-6,6″-(2,2′:6′,2″-terpyridine)diamide are reported here. These new bitopic ligands were found to extract actinides in different oxidation states (U(VI), Np(V and VI), Pu(IV), Am(III), and Cm(III)) from 3 M nitric acid. The presence of three soft nitrogen donors led to the selective extraction of actinides(III) over lanthanides(III) (Ce, Eu) and the presence of two amide functional groups grafted to the terpyridine unit allowed the extraction to occur from a highly acidic medium by minimizing the basicity of the ligand. Ligands bearing long alkyl chains (C4 and C8) or phenyl groups showed increased performances in a polar diluent like nitrobenzene.     

Extraction of Europium(III) into W/O Microemulsion Containing Aerosol OT and a Bulky Diamide. I. Cooperative Effect

Abstract

The extraction of Eu(III) from aqueous HNO₃ solution into a water‐in‐oil (W/O) microemulsion occurring in hexane was studied. Aerosol OT (AOT^?) was used as an anionic surfactant, and a bulky diamide (DA), N,N ^′‐dioctyl‐N,N ^′‐dimethyl‐2‐(3^′‐oxapentadecyl)propane‐1,3‐diamide, was employed as an electrically neutral extractant. The combination of AOT^? and the DA shows a very strong cooperative effect on the metal extraction. The microemulsion containing AOT^? alone in hexane, equilibrated with the acidic solution, is unstable. However, in the presence of the electrically neutral extractant acting as a “masking” ligand to H⁺, the microemulsion in the hexane phase is dramatically stabilized, which enhances the distribution of Eu(III) to the organic phase. The distribution of the metal in the micellar extraction system is also greatly affected by the concentration of an electrolyte, such as HNO₃ or NaNO₃, playing two important roles, i.e., the formation of the microemulsion, “promoting” the metal extraction, and the ion‐exchange of the metal ion for the cation yielded from the electrolyte, contrarily, “suppressing” the metal extraction.     

2,2′‐(Methylimino)bis(N,N‐dioctylacetamide) (MIDOA), A New Tridentate Extractant for Technetium(VII), Rhenium(VII), Palladium(II), and Plutonium(IV)

2,2′‐(Methylimino)bis(N,N‐dioctylacetamide) (MIDOA) was developed as a new extractant for technetium. MIDOA has a similar backbone to TODGA, N,N,N′,N′‐tetraoctyldiglycolamide, where the nitrogen atom bearing a methyl group replaces the ether oxygen in TODGA. MIDOA is highly lipophilic and ready to use in the HNO₃–n‐dodecane extraction system. The distribution ratio (D) for Tc(VII) is extremely high. In addition, Cr(VI), Re(VII), Mo(VI), W(VI), Pd(II), and Pu(IV) are well extracted by MIDOA. MIDOA has high selectivity toward certain oxometallates. The D(Tc) values decrease gradually with HNO₃, H⁺, and NO₃ ^? concentrations, and the log D vs log [MIDOA] dependence indicates the species extracted to be the 1:1 metal‐ligand complex. It is clear that MIDDA [2,2′‐(methylimino)bis(N,N‐didodecylacetamide)] and IDDA [2,2′‐(imino)bis(N,N‐didodecylacetamide)], which have structures analogous to MIDOA, have similar extraction behavior to that of MIDOA.     

Solvent Extraction of Copper from Nitrate Media with Chelating LIX‐Reagents: Comparative Equilibrium Study

Abstract

Comparative experimental studies were carried out on extraction of copper(II) cations from aqueous acid nitrate media using four LIX‐reagents, representatives of different extractant classes: LIX 984N‐I, LIX 860N, LIX 84‐I and LIX 65N. As a diluent, liquid hydrocarbon undecane was used. The extraction behavior of the LIX‐reagents was compared based on an analysis of the influence of the main factors on the two‐phase mass transfer process: aqueous pH‐value, initial copper and extractant concentrations, and temperature. The experimental data received were used in the calculation of important parameters characterizing the efficiency of copper extraction from nitrate media with different LIX reagents: distribution ratios D, concentration extraction constants K _ex, pH_0.5‐values, and thermodynamic parameters such as enthalpy, entropy, and free energy changes (ΔH ⁰, ΔS ⁰, ΔG ⁰‐values).     

Pseudohydroxide Extraction from Aqueous Sodium Hydroxide Solutions with 3,5‐di‐tert‐Butylphenol in Isopar® L Modified with 1‐Octanol

Abstract

Pseudohydroxide extraction (PHE) was investigated for recovering sodium hydroxide (NaOH) from alkaline process solutions. PHE relies on the deprotonation of a lipophilic weak acid by hydroxide ion with concomitant transfer of sodium ion into an organic phase. Contact of the sodium‐loaded organic phase with water results in the reconstitution of the extractant in the organic phase and NaOH in the aqueous phase, thus leading to a process in which NaOH equivalents are transferred from an alkaline feed solution to an aqueous stripping solution. In this work, we investigated PHE using a process‐friendly diluent—Isopar^® L. The lipophilic cation exchanger 3,5‐di‐tert‐butylphenol (35‐DTBP) was used as the extractant. The Isopar^® L diluent was modified with 1‐octanol to improve its solvation properties and the solubility of 35‐DTBP so that practical Na⁺ concentrations could be achieved in the process solvent. The PHE mechanism at process‐relevant conditions was explored by Raman and Fourier transform infrared spectroscopic measurements. Complementary electrospray ionization mass spectrometry studies were also performed. Equilibrium computer modeling suggested that the Na⁺ extraction behavior can be largely explained by the formation of 1∶1 and 1∶2 Na/35‐DTBP species in the organic phase. Extraction isotherms obtained using simulated caustic leaching solutions indicate the potential utility of this approach for recycling NaOH from complex alkaline mixtures.     

Radionuclide Extraction by 2,6‐Pyridinedicarboxylamide Derivatives and Chlorinated Cobalt Dicarbollide

Abstract

The extraction properties of diamide derivatives of dipicolinamide (2,6‐pyridinedicarboxylamide or DPA, (R′R″NCO)₂C₅NH₃) in mixtures containing chlorinated cobalt dicarbollide in the acid form (HCCD), with and without a substituted polyethylene glycol (PEG), have been investigated. Distribution ratios of Cs, Sr, U, Eu and Am have been measured for various concentrations of diamide, PEG, aqueous phase nitric acid, with various HCCD:diamide ratios, and using different organic diluents. In the absence of HCCD, the diamides show little affinity for the extraction of Am or Eu from nitric acid solutions (distributions typically <1). Addition of HCCD with the diamide extractants indicates a pronounced synergistic effect with regard to actinide and lanthanide extraction; the observed Am and Eu distribution ratios typically increase by several orders of magnitude. Cesium is also appreciably extracted by the HCCD in the presence of the various diamides. Addition of PEG (to simultaneously extract Sr) with HCCD and diamide has minimal impacts on the Eu and Am distribution ratios. The initial data indicate that alkyl substituted DPA derivatives weakly affect the extraction properties with regard to actinides and lanthanides, while aryl substituents decrease extraction ability of the mixture. The results of this preliminary work indicate that numerous HCCD‐PEG‐DPA systems are promising and effective for the simultaneous extraction Cs, Sr, Am, and Eu from acidic solutions.     

Liquid‐Liquid Extraction of Tetravalent Hafnium from Acidic Chloride Solutions using Bis(2,4,4‐trimethylpentyl) Dithiophosphinic Acid (Cyanex 301)

Abstract

Liquid‐liquid extraction studies of tetravalent hafnium from acidic chloride solutions have been carried out with bis(2,4,4‐trimethylpentyl) dithiophosphinic acid (Cyanex 301) as an extractant diluted in kerosene. Increase of acid concentration decreases the percentage extraction of metal. Plot of log D vs. log [HCl] gave a straight line with a negative slope of 2±0.1 indicating the exchange of two moles of hydrogen ions for every mole of Hf(IV) extractacted into the organic phase. Extraction of Hf(IV) increases with increase of extractant concentration. The plot of log D vs. log [HA] is linear with slope 2±0.1, indicating the association of two moles of extractant with the extracted metal species. The addition of sodium salts enhanced the percentage extraction of metal, and followed the order NaSCN>Na₂SO₄> NaNO₃>NaCl. Stripping of metal from the loaded organic (LO) with HCl and H₂SO₄ indicated sulphuric acid as the best stripping agent. Increase of temperature increases the percentage extraction of metal indicating the process is endothermic. Regeneration and recycling capacity of Cyanex 301, extraction behavior of associated elements such as Zr(IV), Ti(IV), Al(III), Fe(III), and IR spectra of the Hf(IV)‐Cyanex 301 complex was studied.     

Metal Extraction by Sulfur‐Containing Symmetrically‐Substituted Bisphosphonic Acids. Part I. P,P′‐di(2‐ethylhexyl) Methylenebisthio‐Phosphonic Acid

Abstract

P,P′‐dialkyl methylenebisphosphonic acids are powerful metal extraction reagents exhibiting strong affinity for a variety of metal ions, especially lanthanides and actinides. While the affinity of gem‐bisphosphonic acids is generally high for most metal ions because of their relative high acidity and ability to form six‐member chelate rings, the selectivity often is low. Thus, a strategy of incorporating soft‐donor atoms such as sulfur into gem‐bisphosphonic acids has been adopted to obtain enhanced metal selectivity while retaining high extraction efficiency. To this end a new class of sulfur‐containing gem‐bisphosphonic acid solvent extraction reagents was designed, synthesized, and evaluated for heavy element separations. Specifically, the novel sulfur‐containing P,P′‐di(2‐ethylhexyl) methylenebisthiophosphonic acid, H₂DEH[MBTP], was synthesized, characterized and its aggregation, metal extraction and acid‐base behavior assessed. Vapor phase osmometry measurements indicate that H₂DEH[MBTP] is less aggregated than its P,P′‐di(2‐ethylhexyl) methylenebisphosphonic acid analogue, H₂DEH[MBP], existing in toluene primarily as an equilibrium mixture of monomer and dimer in the concentration range studied. The acid dependency data for the extraction of Am³⁺ and Eu³⁺ from aqueous perchlorate solutions by H₂DEH[MBTP] in o‐xylene exhibit slopes close to ?3 at low acidity, consistent with extraction of a trivalent metal ion. The extractant dependency data exhibit pH dependent slopes, suggesting different stoichiometry of metal extraction under different acidities.