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The equilibrium constant, Kex for the complexation between Co(II) and Cyanex272 in a neutral micelle system, Teric G12A8 (octa-ethylene glycol mono-n-dodecyl ether) was determined and the rate of the reaction was monitored using a combination of stopped flow and UV–vis spectrophotometry. A two-step mechanism was found to fit the experimental data and reaction rate constants for the forward and reverse reactions were obtained. The addition of a cationic surfactant, dodecyl trimethyl ammonium chloride (DTAC) slowed the rate of Co(II) extraction. The effect of charge on the reaction rate could be modelled based on the electrostatic surface potential generated by the added surfactant.

Cobalt extraction by Cyanex 272, Bis(2,4,4-trimethylpentyl)phosphinic acid, (HR) in micellar solution has been shown to be a two-step reversible reaction and the reaction rate constants for the forward and reverse reactions have been obtained. In this investigation the influence of the addition of anionic surfactants, Sodium Dodecyl Sulphate (SDS), on the rate of extraction of cobalt from the aqueous phase by Cyanex 272 in the micelle phase was investigated. The anion surfactant (SDS) was found to increase the rate of extraction. This could be mainly ascribed to the increase in the local concentration of cobalt at the interface generated by the electrostatic surface potential with added surfactant. The effect of charge on the reaction rate has been modelled based on the electrostatic surface potential generated by the added surfactant.

Solvent extraction (SX) is an important separation method with countless applications in the chemical industry. The water/oil interface is an essential feature of SX systems. Microfluidic technology is ideally suited for exploitation in SX due to intrinsic advantages of the micro dimensions that result in laminar flow conditions, high surface-to-volume ratio and the reduced chemical quantities needed. This review describes the use of microfluidic devices in SX. © 2014 Society of Chemical Industry.

Spent pickling acid from the industrial galvanizing process currently requires specialist disposal, yet there is the potential to recover the zinc as a valuable metal. In this work, we compare the extraction of zinc using tributyl phosphate from real galvanizing effluent and laboratory prepared solutions. Both commercial and handmade hollow fiber membrane contactors are used for this purpose. While the zinc is effectively extracted, care must be taken to prefilter the solution upstream of the membrane contactor to minimize crud formation and interfacial effects. The extraction of both zinc and HCl from the effluent is satisfactorily described using mathematical models for both the multicomponent equilibria and mass transfer balances. In development of the multicomponent equilibrium model, the thermodynamic equilibrium constants obtained from the ZnCl2–NaCl–HCl aqueous system were found to be applicable to the ZnCl2–FeCl2–HCl system.

The extraction kinetics of Fe III by di-(2-ethylhexyl) phosphoric acid (D2EHPA) were investigated using a Y–Y shaped microfluidic device. Finite-volume simulations were used to examine the accuracy of a single-step dimeric reaction mechanism in fitting the experimental data. Results demonstrate the validity of the proposed mechanism and show that Fe III extraction occurred at a slow rate (second-order forward rate constant of k 1 = (3.0 ± 0.1) × 10 −6 m 4 /mol s) under a mixed reaction–diffusion resistance regime. The present study provides insight for the control of Fe III extraction rates in hydrometallurgical processes.

Zinc chloride and hydrochloric acid extraction from solutions of high zinc concentration by tri- n -butyl phosphate (TBP) diluted in ShellSol 2046 (an aliphatic solvent) has been studied with a combination of experiments and mathematical modelling. Above 0.4 mol/L aqueous zinc chloride, zinc is extracted predominantly as ZnCl 2 accompanied by small amounts of an acido–metal complex, most likely to be HZnCl 3 . The Pitzer and Hildebrand–Scott models are used to estimate the activity coefficient of ions in the aqueous and organic phase respectively. Both the thermodynamic equilibrium constants and Hildebrand–Scott solubility parameters are fitted for the extracted species: ZnCl 2 (H 2 O) 3 ∙ 3TBP and HZnCl 3 (H 2 O) 3 ∙ 3TBP. The modelling was able to predict both the extraction and stripping processes for aqueous zinc and acid concentration up to 1.6 and 1 mol/L respectively.

A custom built microfluidic device that potentially enables real time monitoring of solute transfer across a water/oil interface is presented and discussed. The device consisted of a Pyrex ® glass, Y-Y shaped microchannel fabricated with an inbuilt UV-Vis detection system. The device was connected to a spectrograph by means of optical fibres for detection of the signal. The device was tested against both a blue coloured dye (waxoline blue) and the metallorganic complex of Co(II) and di (2-ethylhexyl) phosphoric acid (DEHPA). Due to the very short optical path length (~ 10 -4 cm), in situ measurements of highly concentrated analytes are shown to be possible. The use of the device for measurements of concentrated solvent extraction kinetics is envisaged.

Ionic liquids offer an alternative to volatile organic solvents for extraction of a range of materials. This work examines the mass transfer performance of a Karr reciprocating plate column with an ionic liquid as an alternative solvent for the extraction of phenol from water. The results indicate that ionic liquids can be used in existing solvent extraction equipment and that existing correlations and models can be used to predict mass transfer performance.

An investigation of molecular diffusion of solutes across water/oil interfaces in a Y-Y-shaped microchannel with an integrated guide structure is presented. Finite volume numerical simulations were compared with experimental literature data. Analytical approaches including an infinite composite medium model, phase-specific mass transfer coefficient models, and a static transfer cell model were also assessed. An increase in accuracy for the mass transfer coefficient models was achieved by using local coefficients as opposed to length-averaged expressions. The static transfer cell model was shown to improve when based on the interfacial contact time, as opposed to the organic phase residence time. The results presented in this work have immediate application to the determination of kinetic rate constants in reactive mass transfer systems, as considered in Part II of this study (Ciceri et al. Microfluid Nanofluid, 2012).

The use of a microfluidic device in determining the extraction kinetics of CoII ions by di-(2-ethylhexyl) phosphoric acid (DEHPA) was demonstrated. Experimental data obtained using a Y-Y-shaped microchannel were modelled using a finite volume method. The contributions of diffusion and reaction transport resistances to the overall rate of mass transfer were obtained. A diffusion-controlled transfer assumption could not account for the experimental data, confirming that transport occurs under a mixed reaction–diffusion resistance regime. The reaction rate constant was determined to be $$(2.4 \pm 0.6) \times 10^{-10}$$ m/s, in good agreement with corresponding Lewis cell measurements from the literature.

Ionic liquids (ILs) offer a new class of fluids for solvent extraction. This work presents drop size distribution data for the [bmim][PF6]/water system and examines the basis of existing drop size prediction models developed for traditional organic/aqueous systems in a Karr reciprocating plate column and recommends how they may be used for these new class of materials.

The use of ionic liquids (ILs) as alternatives to volatile organic liquids in solvent extraction is being considered in a number of applications. This study presents data on the dispersed phase holdup of the ionic liquid [bmim][PF6] with water in a Karr extraction column. It was found that this system conforms to the standard slip velocity relationships and that the holdup can be predicted using existing correlations for dispersed phase holdup in Karr reciprocating plate columns. This indicates that the incorporation of ionic liquids into existing processing equipment is relatively straightforward and they behave in a predictable manner.

Polytetrafluoroethylene (PTFE) plasma sputtering of polypropylene (PP) membranes allows the formation of an ultrathin fluorinated hydrophobic surface that retains the microporous surface structure of the underlying membrane. The absorption results presented in this paper show that the novel PP membrane material performs well for the separation of CO2 from other gases, using an amine-based solvent. Hollow fiber membrane experiments show that the plasma-treated hollow fiber membrane has a superior CO2 mass transfer rate to untreated PP when coupled with monoethanolamine solvent flowing through the fiber lumen for at least 45 h of absorption time. The CO2 mass-transfer rate through the treated hollow fiber membrane is also comparable with that of other researchers who have absorbed CO2 into amine solvents using PTFE hollow fibers and higher than that measured using packed column technology with structured packing and amine solvents.

In this study, the most appropriate organic phase for the selective extraction of Zn(II) from Australian hot-dip galvanizing effluent streams has been determined. TBP (tributyl phosphate) and Hostarex A226 (diisotridecylamine) were identified as the most favourable for the extraction of zinc ions from a chloride matrix. Two alternatives, Hostarex A324 (tri-iso-octlyamine) and Hostarex A327 (tri-n-octyl/n-decylamine), were also tested. Laboratory scale shake tests were conducted using model solutions containing a range of acid concentrations and zinc concentrations up to 80 g/L. Industrial pickling effluent was used to test the effect of impurities present. The use of TBP was confirmed as the most appropriate extractant.

The diffusion behaviour of Co(II) ion in an aqueous homogeneous system and that of 8-hydroxyquinoline (8HQ) in a heterogeneous liquid–liquid system was measured in a Y–Y shaped microfluidic device. We propose a modified version of a previously published equation for a static system to describe the diffusion behaviour of chemical species in this microfluidic device. Specific adaptations of the original equation to the micro environment are illustrated and discussed. The model proposed successfully fitted the diffusion of Co(II) in a homogeneous system (aqueous solutions) and 8HQ across a water/oil interface. We envisage the application of the proposed equation for the discrimination of the diffusion contribution in solvent extraction kinetic studies.

Metal separation by solvent extraction in macroscopic oil/water systems, is a major operation in several countries. Many studies have been devoted to the design of extractants to target specific metals and the use of additives such as modifiers, surfactants, and a second extractant for better kinetics, ease of processing, improved selectivity, and enhanced interfacial properties in these separation systems. As these are quite complex systems, both experimental and modelling studies can be very difficult. This is especially true when attempting to measure interfacial properties. However, over the years many novel pieces of equipment and experimental techniques have been developed to probe these multicomponent systems. This review investigates the role of additives in solvent extraction for metal separations in macroscopic oil/water systems.

This work presents a study of the use of polypropylene (PP) membranes that have been sputtered with poly(tetrafluoroethylene) (PTFE) in a radio frequency plasma reactor. Plasma treatment results in the deposition of an ultrathin microporous coating which has a high degree of fluorination and nano- and microscale roughness. The treated membrane maintains similar pore characteristics and a similar thickness to untreated PP, and therefore, it is likely that the treatment film provides a negligible resistance to CO2 mass transfer relative to that of the bulk PP membrane. The absorption results presented in this paper show that the plasma-treated membrane has a comparable or superior performance to that of PTFE for CO2 mass transfer into monoethanolamine solvent. A flat sheet membrane configuration is used to test the properties of the material and to show that the treated membrane has a comparable CO2 mass-transfer rate to PTFE after 25 days of solvent exposure. Results suggest that all membrane materials are...

Hydrophobic zeolite was synthesized, modified and characterized for its suitability as a permeable reactive barrier (PRB) material for treatment of hydrocarbons in groundwater. Batch sorption tests were performed along with a number of standard characterization techniques. High and low ionic strength and pH tests were also conducted to determine their impact on hydrocarbon uptake. Further ion exchange tests were conducted to determine the potential for the zeolite to act as both a hydrocarbon capture material and nutrient a delivery system for bioremediation. The zeolite was coated with octadecyltrichlorosilane (C18) to change its surface properties. The results of the surface characterization tests showed that the underlying zeolite structure was largely unaffected by the coating. TGA measurements showed a reactive carbon content of 1-2%. Hydrocarbon (o-xylene and naphthalene) sorption isotherms results compared well with the behaviour of similar materials investigated by other researchers. Ionic strength and pH had little effect on hydrocarbon sorption and the treated zeolite had an ion exchange capacity of 0.3 mequiv./g, indicating it could be utilised as a nutrient source in PRBs. Recycle tests indicated that the zeolite could be used cleaned and reused at least three times without significant reduction in treatment effectiveness.

Surface modifications of natural zeolite were performed by coating it with a chitosan layer. The chitosan coated zeolite (Ch-Z) was protonated with either sulfuric or hydrochloric acid and tested for its suitability to capture nitrate from water at 20 and 4 °C. The surface characterization of the Ch-Z was done by SEM, FTIR, TGA and nitrogen adsorption tests. The results of these tests showed evidence of chitosan coating onto zeolite particles. Ch-Z has comparable capacity to other weak anion exchangers with a nitrate ion exchange capacity 0.74 mmol NO 3 g − 1 (protonated with HCl).

MCM-41 is a synthetic, mesoporous silicate material, which currently has limited use as an industrial catalyst. This material is considered to have good potential for adsorption/separation applications due to its regular hexagonal structure, uniform pore distribution, large surface area and large pore volume. In order to enhance the adsorption of metal ions on MCM-41, a metal ion chelating agent, acetylacetone is added and the capacity of the adsorbent for three divalent metal cations in aqueous solutions; Cu(II), Ni(II) and Co(II) determined. Adsorption isotherms for these metal ions are presented, along with adsorption selectivity with respect to pH. Metal ion adsorption results are compared with published data for solvent extraction systems utilising pure acetylacetone and acetylacetone in benzene. It was found that the MCM-41/acetylacetone system produced equal or better metals removal in comparison to solvent extraction methods for some of the metal species tested. Further, the pH of maximum adsorption is shifted in the MCM-41 system compared with the solvent extraction case, thus presenting the possibility of processing under different conditions.

The use of microfluidic devices as analytical tools to probe the kinetics of interfacial reactions between heterogeneous phases such as those that occur in solvent extraction systems can provide important information on the interfacial processes that control these reactions. A number of studies have proposed the use of microfluidic devices for lab-on-a-chip processing. In either case, a detailed understanding of the hydrodynamic and diffusion behavior of the fluids in these devices is essential.In this study, the diffusion of Co(II) in an aqueous phase and the diffusion of the cobalt(II)-di-(2-ethylhexyl)-phosphate (Co(II)-DEHPA) complex in an organic phase were investigated in a double-Y-type microfluidic device. Diffusion experiments were carried out over a range of flow rates in the laminar flow region of the microfluidic device.A computational Fluid Dynamics (CFD) simulation of the flow field was carried out and the detailed velocity distribution in the channel was obtained; this distribution was used to predict the rate of diffusion of a solute. Furthermore, a simplified calculation mesh was developed for reducing the simulation time. The diffusion coefficients of Co(II) and the Co(II)-DEHPA complex were determined by the simulation to be 6.6×10−10 m2/s and 3.2×10−10 m2/s, respectively.

The effect of the presence of monoethanolamine (MEA) degradation products on membrane hollow fibers was investigated using untreated polypropylene (PP) as a model material. Common amine oxidative degradation products were added to MEA to simulate a degraded solution. The effect of these degradation products on the membrane gas absorption process using PP hollow fiber membrane was quantified. When PP membrane which has been exposed to amine degradation products is used in a membrane gas absorption contactor, the mass transfer rate of CO 2 is reduced relative to the use of unexposed PP. It was found that the presence of oxalic acid reduced the mass transfer rate of CO 2 in MEA most significantly followed by formic acid and then acetic acid. These acids are believed to adsorb into the PP, altering the surface properties and reducing the hydrophobicity of the membrane. This in turn increases the degree of wetting of the membrane pores. The membrane was characterized before and after use in a membrane gas absorption contactor containing degraded MEA solvent and studies showed that membrane pore wetting increased by 22–31% after 69 h of use. SEM images and XPS spectra of exposed PP membrane indicate that wetting may be due to both morphological and chemical changes in the membrane due to contact with the solvent. This study highlights the need to consider reductions in the mass transfer rate of membrane gas absorption processes associated with inevitable changes in the solvent composition that comes with prolonged use.

The extraction and stripping of phenol using a solution of tributyl phosphate in kerosene in a hydrophobic polypropylene hollow fiber membrane contactor has been studied. The effect of the aqueous and the organic phase flow rates on the overall mass transfer coefficient for both extraction and stripping steps was investigated. Experimental values of the overall mass transfer coefficient were determined and compared with predicted values from the resistance in series model. Results showed that the overall mass transfer coefficients for extraction were about one order of magnitude greater than those measured during the stripping process. The experimental values were in good agreement with the predicted values for the extraction module. However, the predicted values were slightly overestimated for the stripping module. The individual mass transfer resistances were analyzed and the rate-controlling steps of mass transfer were also identified in both extraction and stripping modules. The major resistance in extraction and stripping was in the aqueous phase and in the membrane phase, respectively.

This study involves the preparation of a number of polymer inclusion membranes (PIMs) using a variety of commercial solvent extraction reagents immobilized in cellulose triacetate (CTA), cellulose acetate, poly(vinyl chloride) (PVC), PVC co-polymerized with vinyl alcohol and vinyl acetate, and carboxylated PVC. The influence of the molecular structure and physicochemical properties of the extractants studied on their ability to form homogeneous, flexible and mechanical strong PIMs are discussed. The physicochemical properties found to be of most importance in this respect are the extractant's lipophilicity, hydrogen bonding capacity, ability to participate in dipole–dipole interactions and its liquid aggregate state at room temperature.

A porous polypropylene membrane was treated to deposit a thin superhydrophobic coating. Treatment conditions were optimised to maximise the contact angle. A high average static contact angle of 169° was achieved through the creation of a porous and rough surface which is 42° higher than that of an untreated polypropylene membrane and 30° higher than that of a Teflon® membrane. This treatment promises to provide low cost, porous, hydrophobic membranes for use in membrane contacting processes.

The mass transfer of carbon dioxide through hydrophobic membrane materials into aqueous solutions of monoethanolamine has been studied. Microporous polypropylene, polytetrafluoroethylene and polyvinylidene fluoride hollow fiber membranes were compared. Membranes were characterized before and after use and wetting studies showed that the mass transfer resistance increased by 15% for polypropylene after 45 hours. Wetting may be due to membrane degradation as a result of contact with the solvent. This study highlights the need to choose membrane‐solvent systems that utilize a low cost membrane that remains unwetted by the solvent over long periods and when subjected to reasonable solvent‐side pressures.

Molecular dynamic simulation techniques have been used to study the equilibrium configuration of a water/n‐heptane interface. The simulations were carried out using a readily available commercial software package, with Ewald sums to estimate the long‐range interactions. The effect of the interface on the molecular structure of n‐heptane was investigated and the interfacial width estimated from interfacial density profiles. Interfacial tension was evaluated using both the well‐established pressure tensor method as well as the more novel capillary wave theory. The results provide the basis for further study of aqueous/organic interfaces relevant to solvent extraction processes.

For the purpose of capturing CO2 from flue gas the absorption of CO2 into an aqueous solution of monoethanolamine was measured by using a column packed with a novel packing, Super Mini Ring (SMR). The SMR gave a higher absorption performance relative to pall ring packing due to a larger effective surface area and also reduced the frictional pressure gradient. The absorption mechanism was observed to be mainly gas phase controlling. It was concluded that for the treatment of flue gas the SMR packing could reduce the height of the absorption column by 20% relative to a pall ring packed column.

—In this study mesoporous silicates MCM-41 and SBA-15 were investigated for their potential as metal ion-selective adsorbents. The greatest advantage of these materials is their large surface area, uniform pore size and controlled surface chemistry, and hence their potential for adsorption processes. The studies of the adsorption of transition metal ions onto MCM-41 examined the comparative adsorption behavior of Zn(II) and Cu(II), using acetylacetone (Hacac) as a chelating agent. The results showed that the MCM-41/Hacac system has potential as an ion-selective adsorbent material. However, due to the relatively small pore size and potential instability of MCM-41 when immersed in water for long time periods, a second mesoporous silicate, SBA-15, has been investigated. The SBA-15 was coated with octadecyltrichlorosilane (C18), and then loaded with a chelating agent (Cyanex 272) and assessed for its potential as an adsorbent material. The surface-modified SBA-15 has been found to have high metal ion selectivity and extractability, and hence good potential as an alternative to established solvent extraction systems.

The stability of polymer inclusion membranes (PIMs) relative to other liquid membranes is amongst the major reasons for the recent rejuvenation of interest in carrier-mediated transport for selective separation and recovery of metal ions as well as numerous organic solutes. This is reflected by an increasing number of PIM investigations reported in the literature over the last two decades. Given the outstanding performance of PIMs compared to other types of liquid membranes particularly in terms of membrane lifetime, it has been predicted that practical industrial applications of PIMs will be realized in the near future. This review provides a comprehensive summary of the current knowledge relevant to PIMs for the extraction and transport of various metal ions and small organic solutes. PIM studies reported to date are systematically summarized and outlined accordingly to the type of carriers used, i.e. basic, acidic and chelating, neutral or solvating, and macrocyclic and macromolecular. The paper reviews the various factors that control the transport rate, selectivity and stability of PIMs. The transport phenomena observed by various authors are related to the membrane characteristics, physicochemical properties of the target solutes as well as the chemistry of the aqueous solutions making up the source and receiving phases. The results from these studies reveal an intricate relationship between the above factors. Furthermore, while the interfacial transport mechanisms in PIMs are thought to be similar to those in supported liquid membranes (SLMs), the bulk diffusion mechanisms in PIMs governing their permeability and selectivity require better understanding. This review also delineates two mathematical modeling approaches widely used in PIM literature: one uses a set of assumptions that allow the derivation of analytical solutions valid under steady-state conditions only; the other takes into account the accumulation of the target species in the membrane during the initial transport state and therefore can also be applied under non-steady-state conditions. The latter is essential when the interfacial complexation reaction kinetics is slow. It involves more complex mathematics and requires the application of numerical techniques. The studies included in this review highlight the potential of PIMs for various niche applications on a practical scale. The discussions provided, however, also emphasize the need for more fundamental research before any such practical applications of PIMs can be realized. This is specifically important for small organic compounds because to date scientific investigation involving the extraction and transport of these compounds remains limited. Transport mechanisms of small organic compounds are less well understood and are likely to be more complex than those observed with the transport of metal ions.

This investigation examines metal ion adsorption on mesoporous silicate, MCM‐41, synthesized from sodium silicate solution and cethyltrimethylammonium bromide (CTAB). MCM‐41 has potential as an adsorbent material, with a regular hexagonal pore structure, large specific surface area, and large pore volume. The MCM‐41 synthesized for this investigation is characterized using powder X‐ray diffraction and nitrogen adsorption and desorption isotherms data. The adsorption behavior for cadmium(II) and lead(II) onto MCM‐41 was studied by contacting the mesoporous silicate with an aqueous solution of metal salts and acetylacetone. Both Cd2+ and Pb2+ were found to quantitatively adsorb onto MCM‐41. The results of this study suggest that MCM‐41 may have applications in the recovery of toxic metals from waste waters.

Streaming potential measurements have been used to investigate the surface characteristics of ultrafiltration membranes and to determine the interactions between the foulant (in this study, whey protein concentrate) and the membrane. The zeta potential of several membranes as a function of pH before and after fouling, and after cleaning was determined from these measurements. These results were interpreted in terms of the physicochemical properties of the foulant, membrane surface charge characteristics as a function of pH, and water flux recovery for unused, and after fouled and cleaned membranes.

In a recently described model for tissue engineering, an arteriovenous loop comprising the femoral artery and vein with interposed vein graft is fabricated in the groin of an adult male rat, placed inside a polycarbonate chamber, and incubated subcutaneously. New vascularized granulation tissue will generate on this loop for up to 12 weeks. In the study described in this paper three different extracellular matrices were investigated for their ability to accelerate the amount of tissue generated compared with a no-matrix control. Poly-D,L-lactic-co-glycolic acid (PLGA) produced the maximal weight of new tissue and vascularization and this peaked at two weeks, but regressed by four weeks. Matrigel was next best. It peaked at four weeks but by eight weeks it also had regressed. Fibrin (20 and 80 mg/ml), by contrast, did not integrate with the generating vascularized tissue and produced less weight and volume of tissue than controls without matrix. The limiting factors to growth appear to be the chamber size and the capacity of the neotissue to integrate with the matrix. Once the sides of the chamber are reached or tissue fails to integrate, encapsulation and regression follow. The intrinsic position of the blood supply within the neotissue has many advantages for tissue and organ engineering, such as ability to seed the construct with stem cells and microsurgically transfer new tissue to another site within the individual. In conclusion, this study has found that PLGA and Matrigel are the best matrices for the rapid growth of new vascularized tissue suitable for replantation or transplantation.

Ionic liquids have been proposed as replacements for volatile organic solvents (VOSs) by a range of authors, due to their very low vapor pressure, ability to dissolve a range of organic, inorganic, and organometallic compounds, immiscibility with water, and ability to form biphasic systems depending on the choice of cation/anion combination making up the ionic liquid. In this study the room temperature ionic liquid, 1‐butyl‐3‐methylimidazolium hexafluorophosphate [bmim][PF6] was synthesized and a range of physical properties including the interfacial tension, viscosity, and density determined. The distribution of tyramine and 2‐methoxyphenethylamine (MPEA) as a function of pH was determined for the [bmim][PF6] system. This was compared to distribution data obtained for these solutes in conventional organic solvent/water systems: xylene/tributylphosphate (TBP)/water and xylene/Benzyl alcohol (BA)/water.

The kinetics of extraction and the effect of electrostatic surface potential on the nickel(II)/2-hydroxy-5-nonylacetophenone oxime (HNAPO) extraction system were characterised in a non-ionic micellar system. A two step reaction mechanism between nickel(II) and HNAPO was found to satisfactorily explain the observed kinetics. Simulation of the kinetics of the complexation reaction over a wide range of concentrations provided the rate constants for the proposed mechanism. The addition of a cationic surfactant, dodecyl trimethyl ammonium chloride (DTAC), slowed the reaction kinetics, while the inclusion of an anionic surfactant, sodium dodecyl sulphate (SDS), enhanced the reaction kinetics relative to the non-ionic micellar system. The charge effects on the reaction rate could be successfully modelled based on the electrostatic surface potential generated by the anionic and cationic surfactants.

Ultrafiltration of proteins and other compressible material is characterized by a significant transmembrane pressure and is often limited by the formation of a fouling layer. This study examines the compressive rheology of such fouling layers. A model is proposed that can be used to predict the performance of filtration processes where there is significant pressure drop across the clean membrane and the filtration rate is limited by fouling during the filtration cycle. The information required for the model can in principle be obtained from simple centrifuge tests and the clean membrane pressure drop. The model can be used to optimize the cycle times, pressures, and other operating parameters of the ultrafiltration process. The model was tested on the ultrafiltration of whey protein concentrate and shown to describe the experimental data. © 2004 American Institute of Chemical Engineers AIChE J, 50: 1431–1437, 2004

The properties of the nickel(II)/2-hydroxy-5-nonylacetophenone oxime (HNAPO), an active ingredient in LIX 84, extraction system were characterised in a micellar system. The extinction coefficient, λ max of HNAPO (316 nm) and the Ni 2+ complex (387 nm) in a neutral micellar system, poly dispersed octa-ethyleneglycol mono- n -dodecyl ether (G 12 A 8 ) were determined as 3100 and 3500 M −1 cm −1 , respectively. HNAPO was found to have a neutral micellar phase and bulk aqueous phase p K a of 11.5 and 12.5, respectively. The extraction equilibrium constant, K ex, was determined to be 10 −8.0 , and the deviation from theory observed at high pH can be accounted for by consideration of the competition for nickel(II) ions by hydroxide ions and HNAPO. A micellar phase of octa-ethyleneglycol mono- n -dodecyl ether (C 12 E 8 ) was determined to be an appropriate model of the free oil/water interface from the solubilised location of HNAPO. Utilising the interfacial probe, 4-heptadecyl-7-hydroxy coumarin (HHC) allowed the determination of the electrostatic surface potential of mixed micelles of G 12 A 8 and sodium dodecyl sulphate (SDS) or dodecyl trimethyl ammonium chloride (DTAC). The electrostatic surface potential was a linear function of the number of additional surfactant monomers within the G 12 A 8 micelle, for the concentration range studied. For G 12 A 8 /DTAC mixed micelles, the surface potential was given by +1.1 mV per DTAC molecule per micelle, and for G 12 A 8 /SDS mixed micelles the relationship was −1.4 mV per SDS molecule per micelle.

The authors have previously described a model of in vivo tissue generation based on an implanted, microsurgically created vessel loop in a plastic chamber (volume, 0.45 ml) containing a poly(DL-lactic-co-glycolic acid) (PLGA) scaffold. Tissue grew spontaneously in association with an intense angiogenic sprouting from the loop and almost filled the chamber, resulting in a mean amount of tissue in chambers of 0.23 g with no added matrix scaffold and 0.33 g of tissue in PLGA-filled chambers after 4 weeks of incubation. The aim of the present study was to investigate whether a greater volume of tissue could be generated when the same-size vessel loop was inserted into a larger (1.9 ml) chamber. In four groups of five rats, an arteriovenous shunt sandwiched between two disks of PLGA, used as a scaffold for structural support, was placed inside a large polycarbonate growth chamber. Tissue and PLGA weight and volume, as well as histological characteristics of the newly formed tissue, were assessed at 2, 4, 6, and 8 weeks. Tissue weight and volume showed a strong linear correlation. Tissue weight increased progressively from 0.13 +/- 0.04 g at 2 weeks to 0.57 +/- 0.06 g at 6 weeks (p < 0.0005). PLGA weight decreased progressively from 0.89 +/- 0.07 g at 2 weeks to 0.20 +/- 0.09 g at 8 weeks (p < 0.0005). Histological examination of the specimens confirmed increased tissue growth and maturation over time. It is concluded that larger quantities of tissue can be grown over a longer period of time by using larger-size growth chambers.

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The temperature-dependent aggregation in aqueous solutions of self-assembling graft copolymers of Pluronic (PEO−PPO−PEO triblock copolymers) and poly(acrylic acid) (Pluronic-PAA) has been studied using fluorescence techniques (steady-state intensity and depolarization and fluorescence lifetimes). Aggregates that form above the critical micellization temperatures (CMT) are micelle-like, with substantially dehydrated PPO core and hydrated PEO−PAA corona, and provide the physical cross-linking required for gelation. Unexpected hydrophobic domains have been observed below the CMT which provide an environment more hydrophobic than the micelles to pyrene and 1,6-diphenyl-1,3,5-hexatriene (DPH) and are related to the grafting density of the PAA onto the Pluronic copolymers.

The solubility of riboflavin (RF), potassium ferricyanide (K 3 Fe(CN) 6 ) and polar components from yeast extract (YX) in a sodium bis-(2-ethylhexyl) sulfosuccinate (AOT) modified supercritical carbon dioxide (scCO 2 ) system was investigated. The results from RF solubility studies indicate that the microemulsion phase formed by AOT contains a polar core with an effective static dielectric constant of 20±5. Although this core is not indicative of bulk water, the overall improvement in polarity from pure scCO 2 is approximately a factor of 10. K 3 Fe(CN) 6 , a highly ionic compound, could not be solubilised into the modified supercritical fluid, indicating that the core was not sufficiently polar to dissolve highly ionic compounds. Finally, successful extraction of polar compounds from YX demonstrated the potential industrial applications of AOT-modified scCO 2 .

The electrophoretic mobilities of hemoglobin and lysozyme were measured through polycarbonate track-etched membranes of different pore sizes. Together with the zeta potential of the protein-fouled membranes, and measurements of the free-solution mobilities, protein sizes, and membrane pore sizes, the theory of Ennis et al. was tested. The presence of the membrane offered little hindrance to protein transfer when the membrane pore size was large in comparison with the protein size and the thickness of the electrical double layers. Under some solution conditions, protein agglomeration was significant and the interactions between the larger particles, and the membrane pore walls caused a more pronounced reduction in the protein mobility from its free-solution value. Good agreement with the theoretical model was found only for cases where the solution remained as a monodispersed suspension of protein monomers.

Bis(2-ethylhexyl) sodium sulphosuccinate (AOT) was successfully solubilised in supercritical carbon dioxide (scCO2), with ethanol or pentanol as co-solvent. Three molecular spectroscopic probes: methyl orange (MO), 8-hydroxy-1,3,6-pyrenetrisulphonic acid trisodium salt (HPTS), and riboflavin (RF) were used to examine the solubilisation characteristics of the water/scCO2 microemulsions formed with AOT. MO was extracted at various operating conditions, although the wavelength of its solvatochromic absorption maximum was not indicative of bulk water properties. Instead, the spectral results imply that MO may be located at the surfactant/water interface. The highly water-soluble dye HPTS was unable to be extracted into scCO2/AOT/water systems, suggesting that the water in the reverse micelle core was not as polar under supercritical conditions as those at ambient conditions. Finally, RF was extracted into the supercritical phase (40°C, 175 bar) with pentanol co-solvent, with an apparent enhanced uptake compared with the value at 40°C and ambient pressure in bulk water. This appears to be due to the presence of microcrystals dispersed in the supercritical phase.

The effect of viscosity on the critical thickness of film rupture has been investigated using the new technique of dual wavelength ellipsometry. This technique enables accurate film thickness determination of a draining film between an approaching droplet and a liquid/liquid interface. Film drainage data for a polybutene/decane film between a water droplet and a bulk water phase was obtained over a range of film viscosities. Critical film thicknesses showed a dependence upon the film viscosity, and ranged from 1950 to 3454 A for polybutene/decane film viscosities of 6.48–29.30×10 −3 N s m −2 respectively. The magnitude of these critical film thickness values indicate that short range van der Waals forces do not control the rupturing process in the systems studied in this investigation.

The equilibrium and kinetics of the extraction of cobalt (II) by P507 in Teric N9 micelles have been studied. The structure of the (2-ethylhexyl) phosphonic acid mono-(2-ethylhexyl) ester (known as P507), in Teric N9 micelles have been investigated using interfacial tension and fluorescence quenching measurements. It has been found that there is an interaction between these two components and mixed micelles are formed The complex of Co2+ with P507 in Teric N9 aqueous solution has been shown to have a 1:3 stoichiometry and the equilibrium constant has been obtained by slope analysis. The rate of complex formation in the micelle media is very fast with the reaction going to completion in less than 0.2 seconds.

A study of the kinetics of nickel ion extraction by Kelex 100 (7-(4-ethyl-1-methyloctyl)8-hydroxyquinoline) is presented. A reaction scheme is proposed and the kinetics are shown to be controlled by the two parallel initial addition steps. The forward reaction rate constants are determined for these cases. The techniques used to measure the kinetics are, stopped flow where the organic ligand is solubilised in micelles and attenuated total internal reflection spectroscopy (ATR). The first is based on the kinetics at a non-ionic micelle interface and the second at a free aqueous-organic interface. Identical results for the kinetics were obtained from the two techniques when variations in the interfacial pKa's of the Kelex 100 are considered due to variations in the dielectic constants of the two different interfaces investigated.

Data for the kinetics of Cu(II) extraction by P50 (5-nonyl-2-hydroxybenzaldoxime) obtained from the total internal reflectance (TIR) static transfer cell is presented. An interfacial mechanism involving two pararell initial addition steps is proposed and forward rate constants determined. These are discussed in relation to other data available for this system and clearly indicate further work is required in the identification of more general reaction mechanisms.

Metal ion extraction through complexation with an organic soluble ligand is a process widely used in the hydrometallurgy industry for the separation, purification and recovery of many metals. It is now being applied to environmental problems to reduce emissions of heavy metals such as chromium from tanning and chrome plating processing plants. Significant developments in this area include the use of micelle systems to simulate the oil/water interface, NMR studies to ascertain the site of ligand solubilisation, ATR techniques to study kinetics at the liquid/liquid interface, and the use of membrane reactors to limit the loss of organic solvent in the rafinate and so allow the application of this technology to lower concentration feeds.

This paper presents an overview of the processes and mechanisms responsible for the extraction of metal ions from aqueous solution using solvent based chelating reagents. A review of the various techniques for the measurements of extraction kinetics is presented. The different techniques described include quiescent interface apparatus, rapidly stirred cells, the rotating diffusion cell, the single drop technique stopped flow technique using miscellar systems, and ATR spectroscopy. The concluding part of the paper describes the role of interfacial phenomena in liquid-liquid extraction kinetic processes.