Ion-exchange Particles Research Articles

Sorptive Media Biofiltration for Inorganic Nitrogen Removal from Storm Water

Passive biological filtration for nitrate removal from storm-water drainage is challenged by highly transient mass loadings, the need to adequately supply an electron donor, and potential inhibition by dissolved oxygen (DO). An approach to optimizing nitrate removal is to employ a filter medium containing a mixture of ion exchange and electron donor particles, where the former serve to retain nitrate at high loadings and enable biological denitrification to be more effective. Bench scale filtration experiments were conducted using a 50:50 volume mixture of expanded clay particles (Filtralite P) and elemental sulfur pastille. Nitrate reduction was 98% under steady flowrate operation at 30min residence time and 2.1mg∕L influent NO3–N. Step increases in flowrate by factors of 5.2, 11, and 25 resulted in maximum effluent NO3–N of 0.93, 1.54, and 1.87mg∕L, respectively. Substantial nitrate breakthrough occurred even when effluent DO remained close to zero. The results suggest methods by which mixed media denitrification filters can be more effectively designed and operated.

Transport Properties of Highly Ordered Heterogeneous Ion-Exchange Membranes

Model "ordered" heterogeneous ion exchange membranes are made with ion exchange particles heaving ion exchange capacity in the range 3 to 2.5 meq/gr (dry basis) and diameters ranging from 37 to 7 microm and 2 component room-temperature vulcanizing silicon rubber as a polymeric matrix, by applying an electric field normal to the membrane surface during preparation. These membranes were shown to have an improved ionic conductivity compared with "nonordered" membranes based on the same ion exchange content (for instance, at 10% resin content "nonordered" membranes show <10(-5) mS/cm while "ordered" membranes have conductivity of 1 mS/cm). The transport properties of ordered membranes were compared with those of nonordered membranes, through the current-voltage characteristics. Limiting currents measured for the ordered membranes were significantly higher than those of the nonordered membranes with the same resin concentration. In addition, higher limiting currents were observed in ordered membranes as the resin particles became smaller. Energy dispersion spectrometry analyses revealed that the concentration of cation exchange groups on the membrane surface was higher for ordered membrane as compared to that of nonordered membranes. This implies that the local current density for the conducting domains at the surface of the nonordered membranes is higher, leading to higher concentration polarization and, eventually, to lower average limiting current densities. The effect of ordering the particles on the membrane conductivity and transport properties was studied, and the advantages of the ordered membranes are discussed.

Particle-loaded hollow-fiber membrane adsorbers for lysozyme separation

The separation of lysozyme (LZ), a valuable enzyme naturally present in chicken egg white, was carried out using a new type of ion exchange hollow-fiber membranes. Functionalities were incorporated into the polymeric membranes by dispersing ion-exchange resins (IERs) in a microporous structure formed by phase inversion. The obtained hollow-fibers were composed of ion-exchange particles surrounded by a polymeric matrix and possessed both high static and dynamic adsorption capacities of more than 60 mg/ml membrane. The hollow-fiber membrane adsorbers were connected in series with different numbers of fibers thereby increasing the effective thickness and the protein residence time within the module. By choosing appropriate operation conditions, the membranes adsorbed solely LZ from fresh chicken egg white (eventually also the minor component avidin), whereas the adsorption of ovalbumin, ovotransferrin, and other low isoelectric point proteins was negligible. An average separation factor for LZ of about 150 was calculated by numerical integration of the protein concentrations in the elution curve during the filtration run. The effect of the filtration flow rate, protein concentration and ionic strength on the membrane's performance was investigated to determine the optimum operation parameters.

Ion Exchange Resins as Excipients for Drug Delivery: Issues for Reproducible Drug Loading

A method for repeatable loading of propranolol hydrochloride as a model drug onto the ion exchanger Amber- lite TM IRP69 was developed and different parameters for the loading process were evaluated due to their impact of the ex- tent of loading. It was found that the extent of loading in equilibrium is widely independent of the experimental method used. However, a magnetic stirrer comminutes the ion exchanger particles, which hampers repeatable loading processes. For kinetic studies, it was found that the pharmacopoeia dissolution tester gives best repeatable results compared to other stirring devices (magnetic stirrer or shaking bath). Furthermore, evaluation of the loading profiles revealed complex kinet- ics, which can be best described by (at least) two independent processes. In addition, with different ratios between ion ex- changer and propranolol, the degree of loading in the equilibrium follows an adsorption isotherm of the Langmuir type, and predicts loading capacity.

Faradaic double layer depolarization in electrokinetics: Onsager relations and substrate limitations

More often than not, the measurement of interfacial potentials by means of electrokinetic techniques is affected by interfering processes that may relax or even annihilate their primary response function. Among these processes are faradaic ones, provided that the substrate is sufficiently conducting and a redox function is available, and non-faradaic ones, if geometrical constraints are in effect. Ample experimental evidence is available, e.g., in the collapse of streaming potentials generated by metal/electrolyte solution interfaces, the bipolar microelectrodic redox processes in fluidized beds of metallic particles, and the “superfast” electrophoresis of dispersed ion exchanger particles and electron-conducting particles. Common feature of these apparently disparate phenomena is that the lateral electric field is affected by coupling with transversal depolarization fields, or by conductance gradients due to Donnan effects. Recent work has rigorously analyzed the deformation of the lateral electric field in a (streaming potential) slit cell by electron transfer reactions at the interface, taking into account both convective diffusion of the electroactive species and kinetics of the interfacial electron transfer reaction. Here a common, generic basis for faradaic and non-faradaic double layer depolarization is formulated along the lines set by Onsager, and methodologies for retrieving the underlying electrokinetic parameters from experimental data are evaluated. Particular attention is paid to the limitations of double layer polarization, as posed by the substrate.

Optical beam deflection approach for studying ion-exchange reactions occurring at a single ion-exchange resin particle

The optical beam deflection method was applied for exploring chemical reactions occurring at a single particle. A probe beam from a diode laser was introduced into a microscope, and focused to the vicinity of a particle. When a chemical reaction occurs at the surface of the particle, concentration gradients exist in the vicinity of the particle due to the diffusion of chemical species involved in the reaction. Ion exchange reactions occurring at a single particle of ion exchangers were used as model systems. The results showed that the tendency of change in the OBD signal with time is opposite of that seen in the reverse ion exchange reactions, both theoretically and experimentally. Also, the experimental results indicated that the concentration gradients changed with time in the diffusion layer around the particles, implying that the actual reaction-rate determining step was not the particle diffusion but film diffusion.

A study of retention and overloading of basic compounds with mixed-mode reversed-phase/cation-exchange columns in high performance liquid chromatography

The retention and overload of bases were studied on two new mixed-mode, silica based phases possessing ionic carboxylate functionalities of different acidity embedded within a hydrophobic ligand (SiELC Primesep™). At low pH, good peak shapes were obtained for small solute mass, suggesting that the mere presence of a mixed-mode hydrophobic/ionic retention mechanism is not responsible for the poor peak shape that can occur on conventional reversed-phases with ionised silanols. Somewhat inferior, but still acceptable peak shape for bases was obtained on a column containing a mixture of discrete ion exchange and reversed-phase particles (Hypersil Duet). In both types of column, the ionic sites favourably increased the capacity for ionised bases, reducing considerably the deterioration of peak shape with load observed with conventional RP columns. The combined ionic and reversed-phase interaction can give strong retention of bases under certain conditions, necessitating careful choice of stationary and mobile phase.

Removal of As(V) and Cr(VI) Ions from Aqueous Solution using a Continuous, Hybrid Field‐Gradient Magnetic Separation Device

A continuous flow colloidal affinity magnetic separation device is used for the removal of As(V) and Cr(VI) from aqueous solutions. Langmuir isotherms fit the adsorption behavior of the individual ions on Orica MIEX® ion exchange particles. In a mixture of equal weight percent As(V) and Cr(VI), the adsorption of As(V) begins only above a critical cut‐off concentration, implying preferential adsorption of the higher valence ion at the available sites. Cr(VI) is removed selectively from the mixture in the continuous flow device, consistent with the presence of a higher concentration of the higher valence ion in the proximity of a charged (anion‐exchange) surface.

Modeling of protein adsorption to DEAE sepharose FF: Comparison of data with model simulation

The equilibrium and kinetic characteristics of the adsorption of human serum albumin (HSA) and ovalbumin (OVA) to the DEAE Sepharose FF weak anion exchanger were experimentally determined. The rate for protein adsorption was simulated with two different models, the first being based on a single lumped kinetic parameter, while the second includes the individual mass transfer processes occurring prior to the adsorption intervention, i.e., diffusion across the liquid film surrounding individual particles and diffusion within the ion exchanger particle itself. The actual adsorption of OVA to DEAE Sepharose FF in fully mixed stirred vessels and in packed bed columns was consistent with both models. In the case of HSA, however, the adsorption profile in an agitated vessel was consistent only with the pore diffusion model and neither model could correctly predict the latter part of the breakthrough profile observed in packed bed experiments.

Highly conductive ordered heterogeneous ion-exchange membranes

A new method for preparing heterogeneous ion-exchange membranes was developed. It was found that application of an ac electric field during curing of the polymeric matrix resulted in the agglomeration of the ion-exchange particles in long linear chains extending across the membrane. As a result, the percolation threshold for ion conductance was reduced to values more than three to four times smaller than those for membranes with randomly distributed particles. The effect of ordering the particles on the membrane conductivity, swelling properties, ion-exchange capacity and permselectivity is studied. The advantages of the ordered membranes in electrodialysis and fuel cell applications are discussed. The experimental and theoretical aspects of this work were inspired through discussions with Prof. Ora Kedem.

Application of homogeneous and heterogeneous cation-exchange membranes in coagulant recovery from water treatment plant residuals using Donnan membrane process

The Donnan membrane process (DMP) was applied for recovery of alum from water treatment plant residuals or sludge. Alum is widely used as a coagulant in drinking water treatment plants for efficient removals of suspended solids and colloidal particles. The application was studied for two different types of membrane viz. the homogeneous Nafion 117 membrane and the heterogeneous Ionac 3470 membrane. Homogeneous membranes are coherent ion exchanger gels while heterogeneous membranes consist of colloidal ion exchanger particles embedded in an inert binder. In the process, the recovered Al 3+ could be concentrated to a high value of over 4500 mg/L (80% recovery) with Nafion 117, but the recovery was relatively low (25% recovery) with Ionac 3470. Since the Donnan membrane process is driven by the electrochemical potential gradient, the presence of high turbidity and natural organic matters in the sludge did not influence alum recovery and no noticeable membrane fouling was observed even after multiple runs for long hours of operation. The Al 3+ recovery profile led to identification of three zones of mass transport viz. kinetically driven linear zone, equilibrium driven saturation zone and osmosis driven dilution zone. All the three zones were observed in Nafion 117 during a 24 h experimental run. For Ionac 3470, only the linear zone was observed during the experimental period. Osmosis effect was not noted for Ionac 3470. The interdiffusion coefficient value of D Al–H was found to be one order of magnitude greater for Nafion 117. Within an ion exchange membrane, a diffusing ion hops from one charged site to the next and that constitutes the primary intramembrane ion transport mechanism. Scanning electron microphotograph and x-ray fluorescence showed clusters of non-conducting inert phases within the Ionac 3470 membrane containing no ionogenic groups. The lower interdiffusion coefficient for Ionac 3470 was attributed to its larger fraction of the non-conducting phase compared to Nafion 117.

Purification of a diluted nickel solution containing nickel by a process combining ion exchange and electrodialysis

The removal of nickel ions from diluted solution using some ion-exchange resins (Dowex MSC-1, Purolite C 100E, KU 2–8 and Dowex HCR-S) was studied. The purification process involved the use of an electrodialysis-type cell in which the centre compartment was filled with a packed bed of ion-exchanger particles. The Dowex HCR-S resin was shown to be the most suitable material for use in electrodeionization processes. The current efficiency under constant rate of nickel transport to the catholyte reached 14%. The energy consumption, which is needed for removal of 0.35 mol Ni (II) from 1 m3 solution containing 1 mol NiSO4, was estimated as 208 Wh. The apparent diffusion coefficients of Ni(II) ions in the ion exchangers were determined with the electromigration method. These values increased with decrease of the effluent pH and reached 1.30–10−12(DowexMSC-l), 1.36·10−12(Purolite C 100E), 2.69·10−12(KU 2–8), and 4.07·10−12 (Dowex HCR-S) m2 s−1 at pH 2.3–2.5. The largest magnitude of the nickel diffusion coefficient was obtained for the Dowex HCR-S resin, which contains the maximum quantity of functional groups per volume unit. It was found that the mobility of sorbed ions determines the efficiency of the purification process.

Preparation of mixed matrix adsorber membranes for protein recovery

This paper presents a generic technology allowing the incorporation of functional entities into a porous substrate. Various ion exchange particles were incorporated into an ethylene vinyl alcohol (EVAL) copolymer porous matrix by an immersion phase separation process and a heterogeneous matrix, composed of solid particles surrounded by a polymeric film, was formed. The developed concept is flexible and offers the possibility to easily adjust the geometry, the adsorption capacity, as well as the functionality of the structure. A series of fibers as well as flat membranes bearing an adsorptive function and high protein binding capacities were prepared. The membranes were characterized with respect to their morphology, porosity, permeability and adsorption capacity. High values of the protein adsorption capacity (40–45 mg bovine serum albumin (BSA)/ml membrane) were obtained by static adsorption experiments. In a sequential desorption step by changing the pH and/or the ionic strength of the eluent, up to 90% protein recovery can be obtained. Dynamic capacity experiments were performed by flowing the protein solution through a stack of 10 membranes. The protein mass adsorbed per unit of membrane bed was calculated at a breakthrough concentration 10% of the feed concentration. The adsorber membranes can be reused in multiple adsorption/desorption cycles without significant loss of performance.

Nondiffusive mechanisms enhance protein uptake rates in ion exchange particles.

Scanning confocal fluorescence microscopy and multiphoton fluorescence microscopy were used to image the uptake of the protein lysozyme into individual ion exchange chromatography particles in a packed bed in real time. Self-sharpening concentration fronts penetrating into the particles were observed at low salt concentrations in all of the adsorbents studied, but persisted to 100 mM ionic strength only in some materials. In other adsorbents, diffuse profiles were seen at these higher salt concentrations, with the transition region exhibiting a pronounced fluorescence peak at the front at intermediate salt concentrations. These patterns in the uptake profiles are accompanied by significant increases in protein uptake rates that are also seen macroscopically in batch uptake experiments. The fluorescence peak appears to be a concentration overshoot that may develop, in part, from an electrokinetic contribution to transport that also enhances the uptake rate. Further evidence for an electrokinetic origin is that the effect is correlated with high adsorbent surface charge densities. Predictions of a mathematical model incorporating the electrokinetic effect are in qualitative agreement with the observations. These findings indicate that mechanisms other than diffusion contribute to protein transport in oppositely charged porous materials and may be exploited to achieve rapid uptake in process chromatography.

A New Approach in Gastroretentive Drug Delivery System Using Cholestyramine

We prepared cellulose acetate butyrate (CAB)-coated cholestyramine microcapsules as a intragastric floating drug delivery system endowed with floating ability due to the carbon dioxide generation when exposed to the gastric fluid. The microcapsules also have a mucoadhesive property. Ion-exchange resin particles can be loaded with bicarbonate followed by acetohydroxamic acid (AHA) and coated with CAB by emulsion solvent evaporation method. The drug concentration was monitored to maintain the floating property and minimum effective concentration. The effect of CAB: drug-resin ratio (2:1, 4:1, 6:1 w/w) on the particle size, floating time, and drug release was determined. Cholestyramine microcapsules were characterized for shape, surface characteristics, and size distribution; cholestyramine/acetohydroxamic acid interactions inside microcapsules were investigated by X-ray diffractometry. The buoyancy time of CAB-coated formulations was better than that of uncoated resin particles. Also, a longer floating time was observed with a higher polymer:drug resin complex ratio (6:1). With increasing coating thickness the particle size was increased but drug release rate was decreased. The drug release rate was higher in simulated gastric fluid (SGF) than in simulated intestinal fluid (SIF). The in vivo mucoadhesion studies were performed with rhodamine-isothiocyanate (RITC) by fluorescent probe method. The amount of CAB-coated cholestyramine microcapsules that remained in the stomach was slightly lower than that of uncoated resin particles. Cholestyramine microcapsules were distributed throughout the stomach and exhibited prolonged gastric residence via mucoadhesion. These results suggest that CAB-coated microcapsules could be a floating as well as a mucoadhesive drug delivery system. Thus, it has promise in the treatment of Helicobacter pylori.

Fundamental Studies on Ion-Exchanger Phase Absorptiometry

In order to establish the methodology of ion-exchanger phase absorptiometry, fundamental studies on light absorption measurements of ion-exchanger particle layer were made. A considerable amount of the light scattered by the solid phase could be effectively recovered by means of a bundle of optical fibers connected with a photodetector. By using an iodine lamp as the light source, it was confirmed that both Beer's and Lambert's laws were applicable to around 4 to 5 absorbance scale in the ion-exchanger particle layer system and up to the cell length of 4 cm if the Pt tube cell was used.

Continuous protein recovery with a liquid–solid circulating fluidized‐bed ion exchanger

AbstractA liquid–solid circulating fluidized‐bed (LSCFB) ion‐exchange system was developed for continuous protein recovery. It contains a downcomer for protein adsorption and a riser for protein desorption, with ion‐exchange particles circulating continuously between the two columns. Effects of the operating conditions on the hydrodynamics and the continuous ion exchange of bovine serum albumin (BSA) in the system were investigated. Under typical operating conditions, up to 98% BSA was adsorbed in the downcomer (showing a very high efficiency of protein removal from the feed), and an overall protein recovery of up to 84% was obtained in the LSCFB system, indicating that the LSCFB system was a very promising strategy for the continuous recovery of proteins.

Electrodeionization 1: Migration of Nickel ions absorbed in a rigid, Macroporous Cation-exchange Resin

The removal of nickel ions from a packed bed of ion-exchange material under an applied potential is studied. This process involves the use of an electrodialysis type cell in which the centre compartment is filled with a packed bed of ion-exchange particles. The bed width, concentration of nickel in the resin and electrolyte concentration were varied. Emphasis was placed on the rate of nickel migration, current efficiency and the effective mobility of nickel in the system. The purpose of the study is to aid in the development of a system for the continuous removal of heavy metal ions from dilute solutions.

Pore network modelling: determination of the dynamic profiles of the pore diffusivity and its effect on column performance as the loading of the solute in the adsorbed phase varies with time

A three-dimensional pore network model for diffusion in porous adsorbent particles was employed in a dynamic adsorption model that simulates the adsorption of a solute in porous particles packed in a chromatographic column. The solution of the combined model yielded the dynamic profiles of the pore diffusion coefficient of β-galactosidase along the radius of porous ion-exchange particles and along the length of the column as the loading of the adsorbate molecules on the surface of the pores occurred, and, the dynamic adsorptive capacity of the chromatographic column as a function of the design and operational parameters of the chromatographic system. The pore size distribution of the porous adsorbent particles and the chemistry of the adsorption sites were unchanged in the simulations. It was found that for a given column length the dynamic profiles of the pore diffusion coefficient were influenced by: (i) the superficial fluid velocity in the column, (ii) the diameter of the adsorbent particles and (iii) the pore connectivity of the porous structure of the adsorbent particles. The effect of the magnitude of the pore connectivity on the dynamic profiles of the pore diffusion coefficient increased as the diameter of the adsorbent particles and the superficial fluid velocity in the column increased. The dynamic adsorptive capacity of the column increased as: (a) the particle diameter and the superficial fluid velocity in the column decreased, and (b) the column length and the pore connectivity increased. In preparative chromatography, it is desirable to obtain high throughputs within acceptable pressure gradients, and this may require the employment of larger diameter adsorbent particles. In such a case, longer column lengths satisfying acceptable pressure gradients with adsorbent particles having higher pore connectivity values could provide high dynamic adsorptive capacities. An alternative chromatographic system could be comprised of a long column packed with large particles which have fractal pores (fractal particles) that have high pore connectivities and which allow high intraparticle diffusional and convective flow mass transfer rates providing high throughputs and high dynamic adsorptive capacities. If large scale monoliths could be made to be reproducible and operationally stable, they could also offer an alternative mode of operation that could provide high throughputs and high dynamic adsorptive capacities.

Electrodeionization 2 : The migration of nickel ions absorbed in a flexible ion-exchange resin

The removal of nickel ions from a low cross-linked ion-exchange resin using an applied electrical potential gradient was studied. The potential gradient across a bed of ion-exchange particles, in which nickel ions were absorbed, was varied by two methods. One involved a change of cell voltage across beds of constant width, the other a change of bed width at constant cell voltage. In this way, various characteristics concerning the electrodialytic regeneration of a bed of ion-exchange particles in the nickel form were ascertained. The diffusion coefficient, current efficiency and migration rate of nickel in the bed are discussed. It is shown that the current efficiency for the removal of nickel is nearly one hundred percent when the bed is in the nickel form, and that the rate of regeneration is proportional to the cell voltage.