2-ethylhexyl Phosphonic Acid Mono Research Articles

P507-modified magnetic porous carbon derived from metal-organic frameworks for efficient separation of zirconium(IV) and hafnium(IV)

Extractant-based solid phase extraction exhibit practical application potential for efficient separation of Zr(IV) and Hf(IV), where the key is to regulate the host–guest interaction between the guest extraction agents and the host matrices to obtain high performance. However, the current research on the host matrices of extraction agents is insufficient. Leveraging the tunability of metal–organic frameworks (MOFs), we successfully prepared a magnetic MOF-derived porous carbon (C(Zn/Co-ZIF)) with a high specific surface area and Co-Nx active sites as an excellent matrix. This was achieved by deliberately controlling the pore volume and microenvironment through a mixed precursor strategy and high-temperature pyrolysis method. Furthermore, as an excellent extractant for the separation of Zr(IV) and Hf(IV) in solvent extraction, 2-ethylhexyl phosphonic acid mono-(2-ethylhexyl) ester (P507) was carefully selected to modify C(Zn/Co-ZIF) to obtain C(Zn/Co-ZIF)@P507 by impregnation. Impressively, the maximum adsorption capacities of C(Zn/Co-ZIF)@P507 for Zr(IV) and Hf(IV) were up to be 0.58 and 0.39 mmol/g, respectively, while exhibiting excellent separation coefficient. Further mechanism studies indicated that the combination of high specific surface area and abundant Co-Nx active sites of C(Zn/Co-ZIF) leaded to strong interaction with P507, resulting in the excellent adsorption and separation performance of Zr(IV) and Hf(IV) based on the coordination between phosphinic groups of P507 and Zr(IV)/Hf(IV).

Recovery of rare earth elements and thorium from acid leaching residue of ionic rare earth concentrates

The acid leaching residue (ALR) of ionic rare earth (IRE) concentrates containing radioactive elements such as thorium (Th) is classified as low-level radioactive waste. ALR holds valuable strategic resources such as rare earth and Th, while improper long-term heaping storage of ALR poses a substantial environmental risk. This paper proposes a comprehensive process involving low-temperature roasting, hydrochloric acid leaching, single extractant enrichment, and stepwise stripping to recover rare earth elements and thorium from ALR. The achieved leaching efficiencies are 80.11% of LnY, 99.43% of Sc(III), and 98.67% of Th(IV) after the carbonization of the organic phase in the ALR through low-temperature roasting. Despite large amounts of acid and impurities present in the leachate, 2-ethylhexyl phosphonic acid mono 2-ethylhexyl ester (HEHEHP) still exhibits nearly 100% extraction efficiency for Sc(III) and Th(IV). The effective separation of LnY, Th(IV), and Sc(III) was achieved by implementing fractional extraction enrichment of Th(IV) and Sc(III), followed by Th(IV) removal through H2SO4 and Sc(III) removal via NaOH from the loaded organic phase. This scheme successfully achieves a recovery of RE and Th and offers a viable solution for the safe disposal of ALR.

Enhanced molybdenum extraction and purification from acidic lixivium using organophosphorus extractants

Solvent extraction with organophosphorus extractants has potential as a low-cost method for efficient Mo recovery for acidic leaching solutions. However, improved selectivity is required to obtain high-purity Mo products. In this study, various acidic organophosphorus extractants were compared, and 2-ethylhexylphosphonic acid mono-(2-ethylhexyl) ester (P507) was found to be optimal for efficient Mo extraction and Fe separation from acidic leaching solutions. Under the optimized conditions (40 vol% P507, 3:1 organic/aqueous, 20 °C, 5 min), the Mo and Fe extraction efficiencies reached 98.1 % and 35.2 %, respectively, with a separation factor of 90.1. The Mo/Fe separation efficiency was further improved using a two-stage countercurrent extraction method. The Mo extraction efficiency was attributed to coordination bonds (P = O → Mo) formed between Mo(VI) oxycations and P507 dimers, as well as covalent bonds (POMo) formed by substituting the hydrogen ions in P507. Increasing the H2SO4 concentration in the leaching solution gradually transformed MoO22+ into Mo2O52+ dimers, which formed MoO2(HA2)2 and Mo2O5(HA2)2 metal complexes during the extraction process. HCl scrubbing of the loaded organic phase effectively removed Fe. For subsequent ammonia stripping of the HCl-scrubbed organic phase, the optimal ammonia concentration was 1.25 mol/L. Further increasing the ammonia concentration promoted the saponification reaction of ammonia with P507, thereby reducing the Mo stripping efficiency. In summary, using multistage countercurrent extraction, increasing the H2SO4 concentration in the leaching solution, and scrubbing the loaded organic phase with HCl facilitate efficient Mo/Fe separation, providing a feasible approach for the preparation of high-purity ammonium molybdate with broad application prospects.

Specific Ion Effect on the “Water Bridge” Interaction at an Interface: A New Understanding into the Extraction and Separation Selectivity Based upon Competitive Diffusion and Adsorption

Understanding the essence of a specific ion effect on the intermolecular interaction at the near-interface boundary layer during solvent extraction is crucial for developing new approaches to achieve enhanced extraction and separation of various valuable metals from complex aqueous solutions. The present work aims to detect the microscopic effect from competitive diffusion and adsorption of various salt cations in the near-interface boundary layer on their interaction with amphiphilic model molecules, 2-ethylhexylphosphonic acid mono-(2-ethylhexyl) ester (P507), at the air–water interface by using the Langmuir–Blodgett (LB) monolayer technique. It was found that the interaction between cations and P507 molecules through a long-range hydrogen bond “water bridge” confined in the near-interface boundary layer plays a crucial role in determining the difference in the diffusion mass transfer rate of ions with different hydration abilities. Conventional understanding about competitive extraction of various metal cations controlled mainly by their thermodynamic difference in the interaction intensity with the P–O and P═O groups in P507 molecules cannot explain such a kind of specific ion effect on the mass transfer kinetics via ion hydration. Molecular dynamics simulation revealed that the hydration ability of ions is the key factor determining the mass transfer rate and interaction intensity. In the low salt concentration region, the interaction intensity of salt cations with the P–O and P═O groups in P507 molecules is one of the determinants of the competitive adsorption behavior at the interface. However, in a higher salt concentration region, the specific ion salting-out effect via ion hydration becomes significant, causing a decrease in hydration of the target salt cation; therefore, it dominated the diffusion mass transfer rate of ions. This work provides a new insight to understand the kinetic role of competitive diffusion and adsorption of ions in the near-interface boundary layer and their effect on extraction and separation selectivity. It lays the foundation for achieving controllable separation of target metal ions by adjusting the coexisting ion species and their concentrations.

Polymer Inclusion Membranes with P507-TBP Carriers for Lithium Extraction from Brines.

The separation of lithium and magnesium from salt-lake brines with high Mg2+/Li+ ratios is a main challenge for lithium extraction. In this work, novel polymer inclusion membranes (PIMs) were developed by incorporating 2-ethylhexyl phosphonic acid mono 2-ethylhexyl (P507) and tributyl phosphate (TBP) as the carriers into cellulose triacetate (CTA) polymers. The Li+ could be stripped from the P507-TBP extracting carriers using pure water eluents without adding concentrated hydrochloric acid, which can help decrease carriers’ leakage risk from membrane matrixes and keep the stability of PIMs. The morphology, composition, and wettability of P507-TBP-based PIMs were characterized systematically, and the carrier content in the PIM was also optimized. In the transport experiment with the feed of 0.1 mol/L LiCl and 4.0 mol/L MgCl2, the CTA/P507-TBP60% membrane exhibits a Li+ permeability of 4.76 × 10−3 mol·m−2·h−1 and a Li/Mg separation ratio of 10.2. After recycling seven times, the selectivity of the PIM is well-retained (>10), and the permeability of Li+ decreases slightly (less than 15%). With a decent selectivity and excellent stability, PIMs containing P507-TBP carriers show great potential for sustainable and efficient lithium recovery from brines with high Mg/Li ratios.

Behaviors of ALSEP Organic Extractants: an Atomic Perspective Derived from Molecular Dynamics Simulation

ABSTRACT Molecular dynamics simulations were performed on mixtures of N,N,N′,N′-tetra(2-ethylhexyl)diglycolamide (T2EHDGA) and 2-ethylhexylphosphonic acid mono(2-ethylhexyl) ester (HEHEHP) extractants in a dodecane-water system in order to understand the organization and interfacial behavior of extractants in the Actinide-Lanthanide Separation (ALSEP) process. The dynamic behavior and coordination environments of these extractants near the interface were investigated as a function of aqueous nitric acid concentration in the range 0–6 M HNO3. To gain a complete molecular picture of the extractants’ interfacial behaviors, the effects of varying acidity were scrutinized in the context of spatial distributions of extractants within a given phase, chemical interactions, interfacial orientation, and extractant conformation. While the composition of the interfacial solvent mixing region changed with increasing acidity, the behavior of both extractants exhibited very little response to the varying acid levels, but in their own distinct manner. HEHEHP was found to express a specific interfacial behavior marked by a stronger affinity for the interface, with the polar POOH head group being oriented toward the interface and the alkyl chains residing in a constrained conformation. The larger and more flexible extractant, T2EHDGA, is less strongly associated with the interfacial region, on average dwells deeper into the organic phase, and displays orientations and conformations that are more like those of bulk organic phase T2EHDGA molecules than the ordered HEHEHP molecules.

Study on the interfacial behaviors for extraction of heavy rare earths with PC-88A: A new strategy of thin oil film extraction

The traditional organic solvent extraction for selective recovery of target components from low-concentration solutions bears many disadvantages such as high consumption of extractant, low enrichment ratio of target components and multiple extraction stages. To promote extraction and separation of rare earth ions at oil–water two phases interface, a new strategy of thin oil film extraction was suggested in present work for selective recovery of rare earth ions with extremely low concentrations in the leaching solution of ion-adsorption type rare earth ores. Experimental results revealed that the distribution ratio and extraction rate of rare earths can be adjusted by oil film thickness, flow rate of feed liquid, extractant concentration and saponification degree of 2-ethylhexyl phosphonic acid mono (2-ethylhexyl) ester (PC-88A). The interfacial extraction reaction of rare earth ions was a pseudo-first-order reversible reaction in the thin oil film extraction system, conforming to the proposed extraction kinetics model. The change of extraction behaviors was dependent on the orientation, arrangement and mutual interaction behaviors of molecules at oil-water two phases interface. By MD simulations, it indicates that the extraction behavior of Er3+ ions in oil film extraction system has a close relationship with the interfacial behavior of extractant molecule. The present work provides a theoretical basis for developing a new method of strengthening extraction and separation of rare earth ions from low-concentration rare earth solutions.

Extraction kinetics and kinetic separation of La(III), Gd(III), Ho(III) and Lu(III) from chloride medium by HEHEHP

According to the tetrad-effect, 14 elements of lanthanides can be divided into four groups. In our previous study, a new approach was proposed for the kinetic separation of four rare earth ions La(III), Gd(III), Ho(III) and Lu(III) coming from four groups. In that study, four rare-earth ions were kinetically separated from their coexisting mixed aqueous solutions, by performing liquid-column elution using the aqueous solution containing four lanthanide rare-earth ions as the stationary phase and the dispersed organic oil droplets containing HEHEHP (2-ethyl hexyl phosphonic acid mono 2-ethyl hexyl ester) extractant as the mobile phase. The study of extraction kinetics is very important for understanding the kinetic separation of rare earth ions, which was carried out in this paper. The extraction kinetics of La(III), Gd(III), Ho(III) and Lu(III) by HEHEHP diluted in heptane were investigated using single drop method. The different parameters affecting the extraction rate such as column length, specific interfacial area, rare earth ion concentration, extractant concentration, hydrogen ion concentration and temperature were separately studied and the rate equations are deduced. It is first order with respect to rare earth ion and HEHEHP concentrations, and negative first order with respect to hydrogen ion concentrations. The rate constants at 293.15 K are 10−6.23, 10−5.73, 10−5.58 and 10−5.43, respectively. The experimental results demonstrate that the extraction rate of La(III), Gd(III), Ho(III) or Lu(III) is diffusion-controlled, and the extraction reaction takes place at the interface rather than in the bulk phase. The extraction model was proposed. Besides, the kinetic separation of rare earth ions by HEHEHP oil drops was discussed.

Selective Recovery of Molybdenum over Rhenium from Molybdenite Flue Dust Leaching Solution Using PC88A Extractant

Selective solvent extraction of molybdenum over rhenium from molybdenite (MoS2) flue dust leaching solution was studied. In the present work, thermodynamic calculations of the chemical equilibria in aqueous solution were first performed, and the potential–pH diagram for the Mo–Re–SO42−–H2O system was constructed. With the gained insight on the system, 2-ethylhexyl phosphonic acid mono-(2-ethylhexyl)-ester (PC88A) diluted in kerosene was used as the extractant agent. Keeping constant the reaction temperature and aqueous-to-organic phase ratio (1:1), organic phase concentration and pH were the studied experimental variables. It was observed that by increasing the acidity of the solution and extractant concentration, selectivity towards Mo extraction increased, while the opposite was true for Re extraction. Selective Mo removal (+95%) from leach solution containing ca. 9 g/L Mo and 0.5 g/L Re was achieved when using an organic phase of 5% PC88A at pH = 0. No rhenium was coextracted during 10 min of extraction time at room temperature. Density functional theory (DFT) calculations were performed in order to study the interactions of organic extractants with Mo and Re ions, permitting a direct comparison of calculation results with the experimental data to estimate selectivity factors in Mo–Re separation. For this aim, PC88A and D2EHPA (di-(2-ethylhexyl) phosphoric acid) were simulated. The interaction energies of D2EHPA were shown to be higher than those of PC88A, which could be due to its stronger capability for complex formation. Besides, it was found that the interaction energies of both extractants follow this trend considering Mo species: MoO22+ > MoO42−. It was also demonstrated through DFT calculations that the interaction energies of D2EHPA and PC88A with species are based on these trends, respectively: MoO22+ > MoO42− > ReO4− and MoO22+ > ReO4− > MoO42−, in qualitative agreement with the experimental findings.

Nano ZrO2 Synthesis by Extraction of Zr(IV) from ZrO(NO3)2 by PC88A, and Determination of Extraction Impurities by ICP-MS

High purity Zirconium (Zr) materials are essential in many components of nuclear reactors, especially fuel cladding tubes. Due to the matrix influence, determination of impurities in the Zr materials requires separation from the Zr matrix. Among extraction methods, solvent extraction is common and suitable for large-scale production. In this study, extraction capability of Zr(IV) by 2-ethylhexyl phosphonic acid mono 2-ethylhexyl ester (PC88A) was examined by FT-IR and UV of ZrO(NO3)2 salt, PC88A-toluene solvent, and Zr-PC88A-toluene complex. ZrO2 (obtained from Institute for Technology of Radioactive and Rare Elements—ITRRE), after being separated from the Zr matrix, was determined for impurities using internal standard (indium, In) by 50% of PC88A dissolved in toluene. Separation of impurities from the Zr matrix underwent two stages. First, one cycle of extraction of the Zr matrix and impurities in 3 M HNO3 using 50% PC88A/toluene was conducted. Second, impurities were scrubbed by 4 M HNO3 in two cycles. Results revealed that approximately 74% of Zr(IV) was separated to the organic phase and 26% remained in the aqueous phase. Determination of impurities after separation from the Zr matrix by ICP-MS using internal standard in revealed that the recovery of impurities achieved 95–100%. With the mentioned amount of Zr, the effect of the Zr matrix on the determination of elements by ICP-MS is negligible. Levels of impurities have relative standard deviations (RSD) of less than 6.9% and recovery of 88.6–98.8%. Therefore, the determination of impurities has high reliability and accuracy. The back-extraction of Zr(IV) in organic phase by 1 M H2SO4 has stripped about 99.5% of the Zr matrix back to the aqueous phase. Following this, NH3 was added to the solution containing Zr after back-extraction to form Zr(OH)4 which was then desiccated to produce ZrO2. X-ray Diffraction (XRD), Scanning and Transmission Electron Microscopy (SEM and TEM) images showed that the new ZrO2 product has spherical nanostructure with diameters of less than 25 nm, which is suitable for applications for the treatment of colorants, metal ions in wastewater sources and manufacture of anti-corrosion steel. In addition, the energy dispersive X-ray (EDX) of the new ZrO2 product showed that it has high purity.

Radiochemical characterization and decontamination of rare-earth-element concentrate recovered from uranium leach liquors

The paper deals with two rare earth elements (REE) concentrates recovered from uranium leach liquors after sorption separation of uranium. Activity of the REE concentrates was found to be 106 Bq kg−1; Ac-227 and its short-lived daughter products were the main radioactive impurities contributing more than 99% of total activity. Activity of both U-238 + Th-232 in the REE concentrates did not exceed 0.2% of total activity. Extraction by 2-ethylhexylphosphonic acid mono-(2-ethylhexyl) ester (P-507 extractant) in Shelsol D90 diluent was suggested for REE deactivation. It was shown that thorium may be eliminated by extraction in strong acidic media (pH − 0.5 to − 1), whereas radium extraction was suppressed over the whole studied pH range. Further REE separation to heavy and light groups at pH 1 resulted in selective concentration of actinium in light REE group. The suggested separation flowsheet was tested on the real REE concentrate. It was shown that obtaining non-radioactive fraction of heavy REE is possible.

Development of Magnetic Silica Hybrid Material with P507 for Rare Earth Adsorption

A magnetic silica hybrid material (MSHM) containing 2-ethylhexylphosphonic acid mono-(2-ethylhexyl) ester (P507) for rare earth adsorption was developed. Compared with a common grafting preparation method of magnetic silica hybrid material, the developed strategy of embedding the extractant using a sol–gel method revealed simple and efficient advantages. The prepared hybrid materials were analyzed by scanning electron microscopy, Fourier infrared spectroscopy, magnetization, energy dispersive spectrometry, and thermogravimetric analysis. As for the adsorption kinetics, the pseudo-second-order equation fitted well the experimental data. Adsorption of Y(III) using the MSHM fit well with the Langmuir isotherm model rather than the Freundlich isotherm model. The values of thermodynamic parameters at 303 K, 311 K, 318 K, and 333 K were calculated. Hydrochloric acid solution was used for the desorption of Y(III) loaded on MSHM. The effective separation of Y(III) and Eu(III) revealed its potential for phosphor r...

Extraction and separation of Pr(III)/Ce(III) from chloride medium by 2-ethylhexylphosphonic acid mono-(2-ethylhexyl) ester in the presence of two complexing agents

ABSTRACTExtraction and separation of Pr(III)/Ce(III) from a chloride medium using 2-ethylhexylphosphonic acid mono-(2-ethylhexyl) ester in the presence of two water-soluble complexing agents, lactic acid and citric acid, were experimentally studied. By adding the complexing agents into an aqueous chloride medium, the extraction capacity and separation factor were as high as 30.97 g/L and 10.48, respectively, which were much higher than those in conventional solvent extraction systems. The cation-exchange mechanism was also verified by IR spectra. Thus, it was demonstrated that this complexing method can be used as an effective method for improving extraction efficiency and increasing selectivity of adjacent rare earth metals.

Comprehensive appraisal and application of novel extraction system for heavy rare earth separation on the basis of coordination equilibrium effect

Several novel extraction systems were reported since 2-ethylhexyl phosphonic acid mono-(2-ethylhexyl) ester (P507) had been confronted with low selectivity and incomplete stripping for heavy rare earths (HREs). This paper makes a comprehensive appraisal of P507, bis (2,4,4-trimethylpentyl) phosphinic acid (Cyanex272), mixture of P507 and Cyanex272, P507 adding isooctanol and bifunctional ionic liquid extractant (Bif-ILE) [trialkylmethyl-ammonium][di-(2-ethylhexyl)orthophosphinate] ([A336][P507]). Thermodynamics study, apparent kinetics study and theoretical calculation for the cascade extraction are all included. We put forward coordination equilibrium effect for the first time to illustrate the inner and outer environment during the coordination. It could be useful to explain the extraction ability and selectivity of different extractants. All these would provide separation of HREs with more feasible and informative understanding and guidance.

Study on the synergistic extraction of vanadium by mixtures of acidic organophosphorus extractants and primary amine N1923

Abstract In the present study, the solvent extraction of vanadium from chloride medium with acidic organophosphorus extractants, primary amine N1923, and their mixtures were investigated. The organophosphorus acids included di(2-ethylhexyl) phosphoric acid (D2EHPA), 2-ethylhexylphosphonic acid mono-(2-ethylhexyl) ester (HEHEHP), and bis(2,4,4-trimethylpentyl) phosphinic acid (Cyanex272). The extraction effects from chloride medium were studied in detail, illustrating that all the three mixtures of organophosphorus acids and N1923 have synergistic effects on vanadium. As a representative, extraction stoichiometries of vanadium with D2EHPA + N1923 were studied with the methods of slope and constant mole. The extraction capacity of temperature dependency was also investigated. Moreover, the separation of vanadium, nickel, and chromium with mixtures of D2EHPA + N1923 was studied.

Solvent Extraction Separation of Trivalent Americium from Curium and the Lanthanides

The sterically constrained, macrocyclic, aqueous soluble ligand N,N′-bis[(6-carboxy-2-pyridyl)methyl]-1,10-diaza-18-crown-6 (H2BP18C6) was investigated for separating americium from curium and all the lanthanides by solvent extraction. Pairing H2BP18C6, which favors complexation of larger f-element cations, with acidic organophosphorus extractants that favor extraction of smaller f-element cations, such as bis-(2-ethylhexyl)phosphoric acid (HDEHP) or (2-ethylhexyl)phosphonic acid mono(2-ethylhexyl) ester (HEH[EHP]), created solvent extraction systems with good Cm/Am selectivity, excellent trans-lanthanide selectivity (Kex,Lu/Kex,La = 108), but poor selectivity for Am against the lightest lanthanides. However, using an organic phase containing both a neutral extractant, N,N,N’,N’-tetra(2-ethylhexyl)diglycolamide (TEHDGA), and HEH[EHP] enabled rejection of the lightest lanthanides during loading of the organic phase from aqueous nitric acid, eliminating their interference in the americium stripping stages. In addition, although it is a macrocyclic ligand, H2BP18C6 does not significantly impede the mass transfer kinetics of the HDEHP solvent extraction system.

Yttrium extraction from chloride solution with a synergistic system of 2-ethylhexyl phosphonic acid mono-(2-ethylhexyl) ester and bis(2,4,4-trimethylpentyl) phosphinic acid

The extraction of yttrium from chloride medium with a mixture of 2-ethylhexyl phosphonic acid mono-(2-ethylhexyl) ester (HEHEHP, H2A2) and bis(2,4,4-trimethylpentyl) phosphinic acid (Cyanex272, H2B2) in kerosene has been studied. The extraction mechanism was determined by the methods of slope analysis and constant mole. The maximum synergistic enhancement factor of 2.94 was obtained at a HEHEHP/Cyanex272 molar ratio of 1:1. It was found that yttrium was extracted with the synergistic system in the form of Y(HB2)(HA2)2. It is very different from the extraction forms of YH2ClA4 and YH2ClB4 when extracted by HEHEHP and Cyanex272 alone system, respectively. The effects of chloride ion on the yttrium extraction were also studied and the extracted complexes in the organic solution were determined by the infrared spectrum method. It was confirmed that the extraction was via a cation exchange mechanism.

Adsorption properties and mechanism for Fe(III) with solvent impregnated resins containing HEHEHP

Three solvent impregnated resins (SIRs) were first prepared using two types of nonreactive polystyrene-divinylbenzene polymers (HZ818 and HZ830) and one type of reactive weak basic ion exchange resin (D301) as supports and HEHEHP (2-ethylhexyl phosphonic acid mono(2-ethylhexyl) ester) as the extractant. Then the first two prepared SIRs were coated by poly-vinyl alcohol (PVA)-H3BO3 to improve their stability. The two types of coated SIRs were called HZ818-CSIR and HZ830-CSIR, and the third type of SIR was called D301-SIR. The three adsorbents were characterized by scanning electron microscopy and infrared spectrometer. The adsorption properties of iron (III) with three adsorbents were studied by batch method from sulfuric acid medium in the range of pH 0.9–1.9. The optimal pH values of all adsorbents were found at 1.5, and the saturated adsorption capacities of HZ818-CSIR, HZ830-CSIR and D301-SIR were determined as 16.7 mg·g−1, 15.9 mg·g−1 and 25.6 mg·g−1 at 298K, respectively. The adsorption isotherms were found to be fitted with Langmuir isotherms. The adsorption kinetic behaviors of HZ818-CSIR and HZ830-CSIR were fitted with pseudo-second-order kinetic model, while that of D301-SIR with Lagergren first-order kinetic model. The adsorption mechanisms of the three adsorbents were investigated with methods of saturation, equimolar series change and infrared adsorption spectra. It was found that the adsorption mechanism of Fe(III) with HZ818-CSIR and HZ830-CSIR could be deduced as cation exchange between Fe3+ and H+ from P-OH of HEHEHP accompanied with coordination between Fe(III) ion and the phosphoryl oxygen from HEHEHP. While for the D301-SIR, only a cation exchange between Fe3+ and H+ from P-OH of HEHEHP can be proposed.

Solvent extraction of bismuth with 2-ethylhexylphosphonic acid mono-(2-ethylhexyl) ester and 2,2′-bipyridyl

In the present work, the solvent extraction of bismuth with mixtures of acidic phosphorus extractants, di(2-ethylhexyl) phosphoric acid (D2EHPA) and 2-ethylhexylphosphonic acid mono-(2-ethylhexyl) ester (HEHEHP), with some other extractants was investigated including sec-octylphenoxyacetic acid (CA12), sec-nonylphenoxy acetic acid (CA100), 8-hydroxyquinoline (HQ), and 2,2′-bipyridyl (bipy). The extraction effects from nitric acid medium were studied in detail. Results showed that all other mixing systems except HEHEHP+bipy did not have synergistic effects on bismuth. The methods of slope and constant mole were employed to study the extraction of bismuth in HEHEHP+bipy system. Thermodynamic functions and stripping behaviors were also investigated.

Optical Spectroscopy Study of Organic-Phase Lanthanide Complexes in the TALSPEAK Separations Process

Time-resolved fluorescence spectroscopy and Fourier transform IR spectroscopy have been applied to characterize the coordination environment of lipophilic complexes of Eu(3+) with bis(2-ethylhexyl)phosphoric acid (HDEHP) and (2-ethylhexyl)phosphonic acid mono(2-ethylhexyl) ester (HEH[EHP]) in 1,4-diisopropylbenzene (DIPB). The primary focus is on understanding the role of lactate (HL) in lanthanide partitioning into DIPB solutions of HDEHP or HEH[EHP] as it is employed in the TALSPEAK solvent extraction process for lanthanide separations from trivalent actinides. The broader purpose of this study is to characterize the changes that can occur in the coordination environment of lanthanide ions as metal-ion concentrations increase in nonpolar media. The optical spectroscopy studies reported here complement an earlier investigation of similar solutions using NMR spectroscopy and electrospray ionization mass spectrometry. Emission spectra of Eu(3+) complexes with HDEHP/HEH[EHP] demonstrate that, as long as the Eu(3+) concentration is maintained well below saturation of the organic extractant solution, the Eu(3+) coordination environment remains constant as both [HL](org) and [H(2)O](org) are increased. If the total organic-phase lanthanide concentration is increased (by extraction of moderate amounts of La(3+)), the (5)D(0) → (7)F(1) transition singlet splits into a doublet with a notable increase in the intensity of both (5)D(0) → (7)F(1) and (5)D(0) → (7)F(2) electronic transitions. The increased multiplicity in the emission spectra indicates that Eu(3+) ions are present in multiple coordination environments. The increased emission intensity of the 614 nm band implies an overall reduction in symmetry of the extracted Eu(3+) complex in the presence of macroscopic La(3+). Although [H(2)O](org) increases to above 1 M at high [HL](tot), this water is not associated with the Eu(3+) metal center. IR spectroscopy results confirm a direct Ln(3+)-lactate interaction at high concentrations of lanthanide and lactate in the extractant phase. At low organic-phase lanthanide concentrations, the predominant complex is almost certainly the well-known Ln(DEHP·HDEHP)(3). As lanthanide concentrations in the organic phase increase, mixed-ligand complexes with the general stoichiometry Ln(L)(n)(DEHP)(3-n) or Ln(L)(n)(DEHP·HDEHP)(3-n) become the dominant species.