Interfacial activity of metal ion extractant

The interfacial activity of metal ion extractants is discussed. The interfacial tension isotherms are processed by matching the Szyszkowski equation, and estimation of selected parameters to discuss the interfacial activity of extractants. Results are presented in comprehensive tables and figures. The interfacial activity depends mainly on three different parameters; type of extractant, acidity of the aqueous phase and organic diluent. Strongly acidic extractants and protonated amine reagents exhibit the highest interfacial activity. The solvating reagents and non-protonated amines are on the opposite side of the scale, while the chelating reagents are somewhere in the middle. The acidity of the aqueous phase affects the interfacial activity of extractants, mainly by the ionisation (protonation and dissociation) of extractant molecules. Solvating diluents always decrease the interfacial activity of extractants.     

Adsorption at the liquid/liquid interface in mixed systems with hydrophobic extractants and modifiers 1. Study of equilibrium interfacial tension at the hydrocarbon/water interface in binary mixed systems

Equilibrium interfacial tension at the liquid/liquid interfaces for two chelating metal ion extractants, 2-hydroxy-5-nonylacetophenone oxime (HNAF) and 1-phenyldecane-1,3-dion (beta-diketone), two solvating extractants, trioctylphosphine oxide (TOPO) and tributyl phosphate (TBP), and a modifier, decanol, were obtained with a drop volume tensiometer. Moreover, four equimolar binary mixtures of extractant/extractant and extractant/modifier type were considered. The composition of the mixed adsorbed monolayer and the molecular interaction parameters beta were determined by the Rosen equation. It was found that in all the studied systems coadsorption exists; however, synergism in the reduction of interfacial tension was not observed. The obtained results indicate that in the case of three mixtures considered the composition of a mixed monolayer at the hydrocarbon/water interface was quite different from that in the bulk organic phase. Only for the TOPO/beta-diketone mixture were the compositions at the interface and in the bulk organic phase similar. The obtained results indicate that it is impossible to predict the composition of a mixed monolayer by taking into account the interfacial activity of individual components of the mixture. In some cases the compound shows lower interfacial activity (smaller efficiency and effectiveness of adsorption) and occupies a dominant position at the interface, regardless of the type of hydrocarbon used as the organic diluent.     

Interfacial Activity of Trioctyloamine in Hydrocarbon/Water Systems with Nonorganic Electrolytes

Interfacial tension and surface excess isotherms for trioctylamine (TOA) were determined and interpreted. Despite its high hydrophobicity, TOA adsorbs at the hydrocarbon/water interfaces and decreases effectively the interfacial tension, especially in systems containing acidic aqueous phase. Interfacial activity of TOA rises with an increase of the aqueous phase acidity. The effect of amine protonation is clearly observed. Interfacial tension isotherms obtained experimentally can be well matched with the Szyszkowski equation. The interfacial activity of TOA is affected by the type of the organic diluent and the composition of the aqueous phase, i.e., the kind and concentration of nonorganic electrolyte present in the system. Copyright 2001 Academic Press.     

Estimation of trioctylphosphine oxide (TOPO) diffusion coefficients by dynamic adsorption measurements in model extraction systems

Equilibrium interfacial tension and surface excess isotherms for trioctylphosphine oxide (TOPO) were determined and interpreted. Despite its high hydrophobicity, TOPO adsorbs at the hydrocarbon/water interfaces and decreases effectively the interfacial tension. The interfacial activity of TOPO is affected by the type of organic diluent and the composition of the aqueous phase, i.e., the kind (HNO(3), KNO(3)) and the concentration of nonorganic electrolyte present in the system. Significant lowering of TOPO interfacial activity is observed with an increase of the aqueous phase acidity. The dynamic interfacial tension for TOPO was measured by using the drop volume technique. With the aid of the Ward and Tordai equation the values of the diffusion coefficients of TOPO were estimated. The values determined were in the right order of magnitude compared with the literature data.     

Synthesis and primary biological evaluation of 188ReN-NEMPTDD

The recovery of uranium(VI) from chloride solution using a liquid emulsion membrane (LEM) technique was studied. The emulsion is constituted by the quaternary salt of benzyloctadecyldimethyl ammonium chloride (BODMAC, R₄NCl) as a carrier, kerosene as organic diluent, Span 80 as emulsifying agent and 0.5 mol/l Na₂CO₃ as stripping phase. The important variables affecting the LEM permeation process such as the concentrations of extractant, internal strip phase, types of organic diluent, and the presence of magnesium chloride or magnesium sulfate were investigated. It was found that, at a given condition, the maximum extraction rate of uranium(VI) reached 80%. The emulsion was stable at low pH in the presence of certain amounts of electrolytes such as NaCl and MgCl₂.     

Interfacial behavior of Cyanex 302 and kinetics of lanthanum extraction

In this paper, interfacial tension of Cyanex 302 is measured by a Sigma-701 tensiometer and the adsorption parameters are calculated according to the Gibbs and Szyszkowski adsorption isotherms. The interfacial adsorbed behavior of Cyanex 302 is investigated. The results demonstrate that the dimer is the predominant species in the bulk organic phase; however, the monomer is adsorbed at the interface and more interfacially active. The effects of aqueous pH, ion strength, and temperature on the interfacial activity of Cyanex 302 in heptane are discussed and explained in detail. The lower interfacial activity of Cyanex 302 in aromatic hydrocarbon than in aliphatic hydrocarbon has also been determined. The values of interfacial excess at the saturated interface increase in the order n-heptane>cyclohexane>toluene>benzene, which is consistent with the order of extractability of lanthanum by Cyanex 302 in these diluents. The interfacial activity data are used to discuss the kinetic mechanism of lanthanum(III) extraction. It is shown that an interfacial mechanism is very probable, and the extraction limiting step is the reaction between the Cyanex 302 molecules in the organic phase sublayer and the adsorbed intermediate complex.     

Electron transfer mediated by glucose oxidase at the liquid/liquid interface

In order to establish an experimental basis for exploring the reactivity of membrane-bound redox enzymes using electrochemistry at an organic/aqueous interface, the reactivity of glucose oxidase adsorbed at the dichloroethane/water interface has been studied. Turnover of glucose in the aqueous phase mediated by dimethyl ferricenium electrogenerated in the organic phase was measured by measuring the feedback current caused by recycling the mediator as the generator electrode approached close to the interface from the organic side. An unexpected self-exchange reaction of the ferrocene at the interface was suppressed by adsorption of a surfactant. The interfacial enzyme reaction could be distinguished from reaction within the bulk of the aqueous phase. Reaction within a protein-surfactant film formed at the interface is conjectured.     

Polyarylates. V. The influence of phase transfer agents on the interfacial polycondensation

The effect of various phase transfer agents on the interfacial polycondensation of bisphenol A with isophthaloyl chloride was investigated. It was found that the transfer rate of bisphenolate and, thus, the reaction rate of polycondensation were increased with an increasing lipophilicity of the phase transfer agent, i.e. TBAC > TEBAC > TEAC, whereas the equilibrium of bisphenolate between the organic phase and the aqueous phase was hardly affected. Moreover, experimental evidence indicated that a phase transfer agent of high lipophilicity reduced the hydrolysis of the acid chloride, an important aspect in interfacial polycondensation.     

Relationship between interfacial transfer and adsorption-desorption of surface-active bis-ammonium ions at a liquid/liquid interface

Cyclic voltammograms and interfacial tension-applied potential curves were recorded at the interface between water containing surface-active bis-quaternary ammonium ions, bis-A(2+), and an organic solvent such as 1,2-dichloroethane or nitrobenzene. An ordinary diffusion-controlled voltammetric wave for the transfer of bis-A(2+) from aqueous phase to organic phase, the first wave, was followed by a typical adsorption-related wave, the second wave. It was found from the potential dependence of the interfacial tension of bis-A(2+) that the second wave was due to the desorption of bis-A(2+) toward the organic phase. The influence of the structure of bis-A(2+) on voltammograms was investigated, and the potential for the first wave was found to depend on both the length of the side chain and that of the spacer chain, whereas the potential for the second wave depended on the latter only. The thermodynamic relations among three processes of the ion transfer, adsorption, and desorption were discussed based on the experimental results.     

Mass transfer model of triethylamine across the n-decane/water interface derived from dynamic interfacial tension experiments

This publication presents a detailed experimental and theoretical study of mass transfer of triethylamine (TEA) across the n-decane/water interface. In preliminary investigations, the partition of TEA between n-decane and water is determined. Based on the experimental finding that the dissociation of TEA takes place in the aqueous and in the organic phase, we assume that the interfacial mass transfer is mainly affected by adsorption and desorption of ionized TEA molecules at the liquid/liquid interface. Due to the amphiphilic structure of the dissociated TEA molecules, a dynamic interfacial tension measurement technique can be used to experimentally determine the interfacial mass transport. A model-based approach, which accounts for diffusive mass transport in the finite liquid bulk phases and for adsorption and desorption of ionized TEA molecules at the interface, is employed to analyze the experimental data. In the equilibrium state, the interfacial tension of dissociated TEA at the n-decane/water interface can be adequately described by the Langmuir isotherm. The comparison between the theoretical and the experimental dynamic interfacial tension data reveals that an additional activation energy barrier for adsorption and desorption at the interface has to be regarded to accurately describe the mass transport of TEA from the n-decane phase into the aqueous phase. Corresponding adsorption rate constants can be obtained by fitting the theoretical predictions to the experimental data. Interfacial tension measurements of mass transfer from the aqueous into the organic phase are characterized by interfacial instabilities caused by Marangoni convection, which result in an enhancement of the transfer rate across the interface.     

Separation of lignosulfonate from its aqueous solution using supported liquid membrane

This paper presents an experimental and theoretical study on facilitated transport of lignosulfonate (LS) through a flat sheet supported liquid membrane using trioctylamine (TOA) as carrier and dichloroethane as diluent. The studies were carried out with various support materials and operating conditions (viz. carrier concentration, strip phase concentration, salt concentration, etc.) and their effects on the transport of LS. The results were analyzed to identify a suitable combination of support and operating condition that would yield best performance of the supported liquid membrane (SLM) in terms of fast and efficient transport of LS. The stability of the SLM was assessed in terms of loss of liquid from the pores of membrane support. The SLM is found to be stable till 10 h. Co-transport mechanism has been adopted in this work by using NaOH as the strip phase. It was observed that extraction of LS is increased with increase in concentration of NaOH up to a limiting value of 0.5 M NaOH. Difference of salt concentration between feed and strip phase considerably affect the separation process. The diffusional resistances of organic membrane (Δorg) and aqueous solution (Δaq) calculated from the permeation model, which is again a combination of three unique mechanisms viz., diffusion through a feed aqueous layer, a fast interfacial chemical reaction, and diffusion of carrier–complex through the organic membrane, are found to be 609.9 and 176.6 s cm⁻¹, respectively. The values of the diffusion coefficient in the membrane (D_org) and in the bulk organic phase (D_complex) are 1.67×10⁻⁹ and 6.68 × 10⁻⁸ m²s⁻¹, respectively. The extraction of LS is about 90%. Nearly 43% of LS can be recovered at optimum condition.     

Water soluble crown ethers: selective masking agents for improving extraction-separation of zinc and lead cations

The presence of crown ethers 12C4, 15C5 and 18C6 (CE) in aqueous phase influences extraction-separation of zinc and lead ions (M²⁺) by acidic extractant bis(2-ethylhexyl)phosphoric acid (DEHPA) in cyclohexane. In fact, higher complexing ability of the crown ethers towards lead ions causes a greater shift toward higher pH region of the extraction curves versus aqueous phase pH, and consequently an enhancement in the extraction selectivity. The order of extraction selectivity in the presence of the crown ethers varies as 18C6 > 15C5 > 12C4. The analysis of extraction data allows evaluating the stability constants of [M?CE]²⁺ complexes in the aqueous phase. It is demonstrated that the influence of aqueous crown ethers on the extraction process is deeply affected by the organic diluent used. The influence of temperature on the extraction process was studied in the range 286–302 K. This study lets estimating the thermodynamic parameters, i.e., free-energy (ΔGº), enthalpy (ΔΗº), and entropy (ΔSº) changes associated with the extraction process as well as the complexation of cations by the crown ethers in water.     

Isotope exchange between U/III/ and U/IV/ in the HCl-TBP extraction system

The measurement of the isotope-exchange reaction between U/IV/ in the organic phase and U/III/ in the aqueous phase in the extraction systems: 7-8M HCl—5–40% TBP /aromatic diluent or CCL₄/ were made. The high rate of exchange with the rate constant >10²M^–1min^–1 was observed.     

Studies on emulsion liquid membrane extraction of cephalexin

An experimental study on batch extraction of cephalexin using an emulsion liquid membrane system has been reported. The effects of surfactant, carrier and solute concentrations, phase volume ratio, stirring speed, and counterion concentration on the extraction rate were examined. Surfactant, carrier and diluent used were Span-80, Aliquat-336 and n-heptane–kerosene (1:1), respectively. Under the optimised experimental conditions, emulsion swelling was found to be marginal. By maintaining an appropriate pH gradient in the feed and receiving aqueous phase, facilitated transport could be realised. Selective separation of cephalexin from a mixture of 7-aminodeacetoxy cephalosporanic acid (7-ADCA) could be demonstrated in the emulsion liquid membrane system. A mathematical model based on mass transfer across aqueous boundary layer, interfacial chemical reaction and diffusion in the emulsion globule provides a reasonable fit of the experimental solute concentration versus time profiles in the emulsion liquid membrane system.     

Interfacial behavior of DEHEHP and the kinetics of cerium(IV) extraction in nitrate media

The effects of diluents, temperature, acidity, and ionic strength of the aqueous phase on the interfacial properties of DEHEHP have been extensively investigated using the Du Nouy ring method. In addition, the effect of cerium(IV) concentration loaded in the organic phase on the interfacial tension has also been studied. With the increase of DEHEHP concentration, the value of interfacial tension (gamma) decreases in the studied system, which shows that DEHEHP has interfacial activity as a kind of surfactant. The surface excess at the saturated interface (Gamma(max)) and the minimum bulk concentration of the extractant necessary to saturate the interface (C(min)) under the different conditions are calculated according to two adsorption equations such as the Gibbs and Szyszkowski functions to be presented in comprehensive tables and figures. The relationship between the interfacial activity of DEHEHP and cerium(IV) extraction kinetics by DEHEHP has been discussed by considering different factors such as the effects of diluents and temperature. However, the interfacial activity parameter of extractant only is a qualitative parameter, but cannot provide strong enough evidence to quantitatively explain the relationship between extraction kinetics and interfacial properties of an extractant.     

Interactions in the aqueous phase and adsorption at the air–water interface of caseinoglycomacropeptide (GMP) and β-lactoglobulin mixed systems

The aim of this work was to study the interactions and adsorption of caseinoglycomacropeptide (GMP) and GMP:β-lactoglobulin (β-lg) mixed system in the aqueous phase and at the air–water interface. The existence of associative interactions between GMP and β-lg in the aqueous phase was investigated by dynamic light scattering, differential scanning calorimetry (DSC), fluorometry and native PAGE-electrophoresis. The surface pressure isotherm and the static and dynamic surface pressure were determined by tensiometry and surface dilatational properties. The results showed that GMP presented higher surface activity than β-lg at a concentration of 4% wt but β-lg showed higher film forming ability. In the mixed systems β-lg dominated the static and dynamic surface pressure and the rheological properties of interfacial films suggesting that β-lg hinders GMP adsorption because, in simple competition, GMP should dominate because of its higher surface activity. The surface predominance of β-lg can be attributed to binding of GMP to β-lg in the aqueous phase that prevents GMP adsorption on its own.     

Reversed-phase systems for the separation of pentapeptides by high-performance liquid chromatography

Summary Reversed-phase systems using octyl modified silica as such and as a support for dynamically coated ion-exchangers, were investigated for their ability to separate pentapeptides. Normal reversed-phase adsorption with C-8 bonded silica in combination with citrate bufferpropanol-1 mixtures were found useful for the separation of a number of pentapeptides. The separation of pentapeptides differing widely in retention can be speeded up by applying an organic modifier and/or sodium citrate gradient. A solvent generated cation-exchange system with sodium dodecylsulfate as surfactant showed a high selectivity for the pentapeptides under investigation and is better for analytical purposes than the normal reversed-phase adsorption systems investigated. With respect to the detection of pentapeptides with fluorescamine, the use of dry pyridine as a basic buffer and as diluent for the fluorescamine was also investigated. Compared to the commonly used diluent acetone, pyridine is better when using acidic eluents of moderate buffer strength. At pH>6 no significant differences in sensitivity between acetone and pyridine could be noticed.     

Uranium(VI) extraction with benzyloctadecyldimethylammonium chloride (BODMAC) from chloride and sulfate solutions

Summary The solvent extraction of uranium(VI) from concentrated chloride solutions by quaternary salt benzyloctadimethylammonium chloride (BODMAC, R₄NCl) in three diluents was studied. The composition of the extracted species was R₄N^. UO₂Cl₃and (R₄N)₂^. UO₂Cl₄in the three diluents investigated. The dependence of the distribution ratios on the concentration of hydrochloric acid, extractant, salting-out agents and temperature was investigated. The extraction efficiency of BODMAC strongly depends on the nature of the diluent. The presence of Mg(SO₄)₂basically alters the sequence of diluent extraction efficiency.     

Competitive transport of seven metal cations through bulk liquid membrane using 5,12-di(phenoxymethyl)-1,4-dioxa-7, 10-dithiacyclododecane-2,3-dione as carrier

The competitive metal ion transport of copper(II), cobalt(II), zinc(II), cadmium(II), silver(I), chromium(III) and lead(II) with a S-O donor compound was examined. Competitive transport experiments involving the metal cations from an aqueous source phase through an organic membrane into an aqueous receiving phase have been carried out using 5,12-di(phenoxymethyl)-1,4-dioxa-7,10-dithiacyclododecane-2,3-dione as the ionophore present in the organic phase. Fluxes and selectivities for competitive metal cations transport across bulk liquid membranes have been determined in a variety of chlorinated hydrocarbon and aromatic hydrocarbon solvents. The membrane solvents include: dichloromethane (DCM), chloroform (CHCl₃), 1,2-dichloroethane (1,2-DCE), and nitrobenzene (NB) and also in chloroform-dichloromethane (CHCl₃-DCM) and chloroform-nitrobenzene (CHCl₃-NB) binary mixtures. Although the selectivity for silver(I) cation in all of these organic solvents is fundamentally similar, but the most transport rate for Ag(I) was obtained in dichloromethane. The sequence of transport rate for silver ion in organic solvents was: DCM > CHCl₃ > 1,2-DCE > NB. A linear relationship was observed between the transport rate of silver ion and the composition of CHCl₃-DCM, but a non-linear behavior was observed in the case of CHCl₃-NB binary solution. The influence of the stearic, palmetic and oleic acids as surfactant in the membrane phase on the transport of the metal cations was also investigated.     

稀释剂极性对萃取动力学的影响 I: HEHEHP萃取Fe(Ⅲ)

考察了正辛烷等六种常用稀释剂中2-乙基己基膦酸单2-乙基己基酯从硝酸介质中萃取Fe(Ⅲ)的动力学行为。观察到稀释剂的极性不仅影响萃取速率的大小,而且会引起萃取过程控制模式的改变, 即随着稀释剂极性的增加, 萃取过程由界面化学反应和水相化学反应共同控制模式向单一的界面化学反应控制模式转变。