Influence of Al_(2)O_(3)/SiO_(2) Ratio on the Structure and Properties of Na^(+)/K^(+)Ion Exchange Na_(2)O-MgO-Al_(2)O_(3)-SiO_(2) Glasses

In this work,the structure,viscosity and ion-exchange process of Na_(2)O-MgO-Al_(2)O_(3)-SiO_(2) glasses with different Al_(2)O_(3)/SiO_(2) molar ratios were investigated.The results showed that,with increasing Al_(2)O_(3)/SiO_(2) ratio,the simple structural units Q_(1) and Q_(2) transformed into highly aggregated structural units Q_(3) and Q_(4),indicating the increase of polymerization degree of glass network.Meanwhile,the coefficient of thermal expansion decreased from 9.23×10^(-6)℃^(-1) to 8.88×10^(-6)℃^(-1).The characteristic temperatures such as melting,forming,softening and glass transition temperatures increased with the increase of Al_(2)O_(3)/SiO_(2) ratio,while the glasses working temperature range became narrow.The increasing Al_(2)O_(3)/SiO_(2) ratio and prolonging ion-exchange time enhanced the surface compressive stress(CS)and depth of stress layer(DOL).However,the increase of ion exchange temperature increased the DOL and decreased the CS affected by stress relaxation.There was a good linear relationship between stress relaxation and surface compressive stress.Chemical strengthening significantly improved the hardness of glasses,which reached the maximum value of(622.1±10)MPa for sample with Al_(2)O_(3)/SiO_(2) ratio of 0.27 after heat treated at 410℃for 2 h.

Separation of macro amounts of tungsten and molybdenum by ion exchange with D309 resin

Based on the difference in tendency to polymerize between tungsten and molybdenum, a new method using D309 resin was propounded. The batch tests indicate that the optimum pH value and contact time for the separation are 7.0 and 4 h respectively, the maxium separation factor of W and Mo is 9.29. And the experimental resules show that isothermal absorbing tungsten and molybdenum belongs to Langmuir model and Freundlich model respectively, and the absorbing kinetics for tungsten is controlled by intra-particle diffusion. With a solution containing 70 g/L WO3 and 28.97 g/L Mo, the effluent with a mass ratio of Mo to WO3 of 76 and the eluate with a mass ratio of WO3 to Mo of 53.33 are obtained after column test.

Development of Prolonged Release Microspheres of Metformin Hydrochloride Using Ion Exchange Resins

Aim To prepare the prolonged-released microspheres of mefformin hydrochloride. Methods Ion-exchange resin-drug mefformin hydrochloride complexes were prepared as core materials, and followed by coating using ethylcellulose （EC） by the emulsion solvent diffusion technique. The release rate of mefformin from the microcapsules was highly dependent on the encapsulating formulation, thus being used as an index for formulation screening. Orthogonal experiments were performed to optimize the coating formulation. Results The final chosen formulation for coating of mefformin microcapsules were as follows： （ 1 ） the ratio of EC （20cps） to EC （45cps） was 50：50; （2） the ratio of plasticizer to coating materials was 20% ;and （3） the ratio of resin-mefformin complexes to coating materials was 5 ： 1. Conclusion The prolonged release microspheres of mefformin hydrochloride were successfully prepared.

Pb(Ⅱ) biosorption using chitosan and chitosan derivatives beads: Equilibrium, ion exchange and mechanism studies

The study examined the adsorption of Pb（II） ions from aqueous solution onto chitosan, chitosan-GLA and chitosan-alginate beads. Several important parameters influencing the adsorption of Pb（II） ions such as initial pH, adsorbent dosage and different initial concentration of Pb（II） ions were evaluated. The mechanism involved during the adsorption process was explored based on ion exchange study and using spectroscopic techniques. The adsorption capacities obtained based on non–linear Langmuir isotherm for chitosan, chitosan-GLA and chitosan-alginate beads in single metal system were 34.98, 14.24 and 60.27 mg/g, respectively. However, the adsorption capacity of Pb（II） ions were reduced in the binary metal system due to the competitive adsorption between Pb（II） and Cu（II） ions. Based on the ion exchange study, the release of Ca2＋, Mg2＋, K＋ and Na＋ ions played an important role in the adsorption of Pb（II） ions by all three adsorbents but only at lower concentrations of Pb（II） ions. Infrared spectra showed that the binding between Pb（II） ions and the adsorbents involved mostly the nitrogen and oxygen atoms. All three adsorbents showed satisfactory adsorption capacities and can be considered as an efficient adsorbent for the removal of Pb（II） ions from aqueous solutions.

Adsorption of Ce(Ⅳ) Anionic Nitrato Complexes onto Anion Exchangers and Its Application for Ce(Ⅳ) Separation from Rare Earths(Ⅲ)

Ce （Ⅳ） nitrato complexes were adsorbed on two anion exchangers based on polyvinyl pyridine （PVP） and quatemized PVP incorporated into porous silica matrix. The effect of nitric acid concentration （0.5～6 mol·L^-1） and temperature （278 ～318 K） on Ce（ Ⅳ ） sorption efficiency was investigated. Sorption increased with increasing nitric acid concentration, indicating that [Ce（NO3）6]^2- complex is the main adsorbed Ce（Ⅳ） species. Oxidation of sorbents by adsorbed Ce （ Ⅳ ） species resulting in Ce （ Ⅲ ） release to the solution was observed. Pyridine based anion exchangers exhibited higher oxidation stability compared to the commercial strong base anion exchanger. Ce（ Ⅳ ） reduction was temperature dependent and obeyed pseudo-first-order reaction kinetics. Column separation of Ce （ Ⅳ ） from La （ Ⅲ ） and Y （ Ⅲ ） was carried out from 6 mol·L^-1 nitric acid with PVP based anion exchanger. Reasonable Ce （Ⅳ） breakthrough capacity （0.7 mol·kg^-1 PVP） was achieved. No remarkable decrease of capacity was observed within 3 consequent runs. In contrast, Ce （Ⅲ） leakage due to reduction decreased and breakthrough capacity slightly increased. This effect was more pronounced with increasing temperature. Regeneration with 0.1 mol·L^- 1 nitric acid was successful （recovery 100% ± 4% ） and Ce solution of high purity （ 〉 99.97% ） with respect to La and Y content was gained.

Study on the influence of humic acid of different molecular weight on basic ion exchange resin's adsorption capacity

In this paper, humic acid （HA） was ultra-filtered into different molecular weight sections and was characterized by multielement analysis, UV254/TOC, FT-IR and three-dimensional fluorescence spectrometric. Since humic acids of different molecular weights have different hydrophilic and molecular size, the maximum adsorption capacity of basic ion exchange resins appears on the humic acid whose molecular weight ranges from 6000 to 10,000 Da.

Removal of tungsten and vanadium from molybdate solutions using ion exchange resin

The removal of tungsten(W)and vanadium(V)from molybdate solutions was studied using the poly hydroxyl chelating resin D403in batch and column experiments.The batch experiments indicated that tungsten and vanadium could be preferentially adsorbed by the D403resin for4h in molybdate solution at a pH of approximately9.25.Separation factors,αVMo andαWMo,wereabove45and18,respectively,when the molar ratios of Mo/V and Mo/W in the solution exceeded40.Elution tests illustrated that vanadium and tungsten could be easily eluted from the resin with1mol/L sodium hydroxide solution in only1h.To further explore the sorption mechanism of the resin,the experimental equilibrium isotherm data of the three metals fitted well with the Freundlich model.The column experiments confirmed the adaptability of the D403resin in the production of sodium molybdate with a removal rate of tungsten surpassing90%and that of vanadium of99.4%.

Synthesis, structure characterization, and ion exchange properties of a novel open-framework ecomaterial silicotitanate

A novel open-framework ecomaterial silicotitanate (Na_4Ti_4Si_3O_(10)) wassynthesized by a combination of solgel and hydrothermal methods. The investigation on ion exchangeproperties shows that Na_4Ti_4Si_3O_(10) exhibits high ad-sorption for cesium, i.e., K_d is as highas 60 000 mL/g in neutral solution. The crystal structure of Na_4Ti_4Si_3O_(10) was characterized byX-ray difiraction (XRD), scanning electronic microscope (SEM), transmission electron microscope(TEM), Raman spectrum, differential thermal and thermogravimetric analysis (DTA/TGA), inductivelycoupled plasma (ICP), and X fluorescence analysis. The compound is tetragonal, P4_2, a=b = 0.781 10nm, c = 1.196 45 nm, alpha =beta = gamma = 90 deg, Z = 4, and R^a = 0.041; Na_4Ti_4Si_3O_(10) has athree dimensional framework consisting of Ti-O octahedral clusters and Si-O tetrahedra. The resultsshow that Na_4Ti_4Si_3O_(10) has good chemical stability, thermal stability, and high cesium ionexchange capacity in the whole pH range.

Direct extraction of Mo(VI) from acidic leach solution of molybdenite ore by ion exchange resin:Batch and column adsorption studies

The adsorption behavior of ion exchange resin D301 in the extraction of hexavalent molybdenum from high acidic leach solution was investigated. SEM, EDS and Raman spectra analyses were applied to studying the adsorption capacity, reaction kinetics and possible adsorption mechanism in detail. Results showed that the adsorption capacity of D301 resin for molybdenum from high acidic leach solution was up to 463.63 mg/g. Results of the kinetic analysis indicated that the adsorption process was controlled by the particle diffusion with the activation energy 25.47 k J/mol（0.9-1.2 mm） and 20.38 k J/mol（0.6-0.9 mm）. Furthermore, the molybdenum loaded on the resin could be eluted by using 2 mol/L ammonia hydroxide solution. Besides, dynamic continuous column experiments verified direct extraction of molybdenum from acidic leach solutions by ion exchange resin D301 and the upstream flow improved dynamic continuous absorption.

Implications from protein uptake kinetics onto dextran-grafted Sepharose FF coupled with ion exchange and affinity ligands

Our previous studies have reported the presence of "chain delivery" effects of protein adsorption onto ion exchangers with polymer-grafted ion-exchange groups, such as dextran-grafted and poly(ethylenimine)-modified Sepharose gels. However, it is unclear if the "chain delivery" occurs on affinity adsorption with specific interactions. This work is designed to address this issue. A dextran-grafted Sepharose gel was prepared, and then the matrix was modified using diethylaminoethyl, a typical ion-exchange group, or octapeptide(FYCHWQDE), an affinity ligand for human immunoglobulin G(h Ig G) to prepare ion-exchange or affinity adsorbents, respectively.Results of h Ig G adsorption showed that the uptake rate represented by the effective diffusivity of h Ig G onto the dextran-grafted ion exchangers was obviously enhanced by the dextran grafting, indicating the presence of"chain delivery" of the bound proteins on the charged groups on the dextran chains. By contrast, the effective diffusivity of h Ig G changed little as ligand density increased on the dextran-grafted FYCHWQDE adsorbents.Their adsorption capacities decreased and effective diffusivities were not accelerated by the dextran grafting.Thus, this work clarified that grafted dextran could not accelerate h Ig G uptake rate on the affinity resins, or in other words, chain delivery did not occur on the specific interaction-based affinity adsorption.

A novel protein refolding method integrating ion exchange chromatography with artificial molecular chaperone

Artificial molecular chaperone （AMC） and ion exchange chromatography （IEC） were integrated, thus a new refolding method, artificial molecular chaperone-ion exchange chromatography （AMC-IEC） was developed. Compared with AMC and IEC, the activity recovery of lysozyme obtained by AMC-IEC was much higher in the investigated range of initial protein concentrations, and the results show that AMC-IEC is very efficient for protein refolding at high concentrations. When the initial concentration of lysozyme is 180 mg/mL, its activity recovery obtained by AMC-IEC is still as high as 76.6%, while the activity recoveries obtained by AMC and IEC are 45.6% and 42.4%, respectively.

Adsorption behavior of Sb(Ⅲ) in single and binary Sb(Ⅲ)-Fe(Ⅱ) systems on cationic ion exchange resin: Adsorption equilibrium, kinetic and thermodynamic aspects

The present study dealt with the mechanism of competitive adsorption of Sb(Ⅲ)and Fe(Ⅱ)ions from a copper-containing aqueous solution on Purolite S957,a commercially available cationic ion-exchange adsorbent.Experiments were conducted using aqueous copper sulfate solutions containing either single or conjoint ions,using both sedentary and batch adsorption techniques to ascertain the sensitivity of the adsorption process to variation in p H,mass of resin,contact time,and temperature as well as establishing the optimal range of variables for maximum ion removal.The data from single ion adsorption tests were fitted by non-linear regression techniques to Henry,Langmuir,Freundlich,Temkin,and Dubinin–Radushkevich isotherm models.Freundlich isotherm for Sb(Ⅲ)and Freundlich and Henry models for Fe(Ⅱ)solutions best express the adsorption equilibrium data;while for binary ion electrolytes,the extended Freundlich model fitted the data satisfactorily.The kinetic model adequately describing adsorption was shown to be the pseudo-first-order,underscoring the dominant role of physical adsorption playing in the process.Thermodynamic parameters for the adsorption process reveal differences in the Sb(Ⅲ)adsorption mechanism from single ion and Sb(Ⅲ)-Fe(Ⅱ)containing electrolytes.The adsorption of Sb(Ⅲ)alone is endothermic,whereas the process becomes exothermic in the Sb(Ⅲ)-Fe(Ⅱ)system.

Removal of impurities from scandium solutions by ion exchange

A process of removing impurities,such as Fe,Zr,Ti,Al,Si,from scandium solution by ion exchange was proposed.Various resins’selectivity was studied in scandium chloride solution.The results indicated that D851resin had high selectivity of Sc at low acidity,and high selectivity of Zr at high acidity;D370resin had high selectivity of Fe and Si in high acidity.A new technical process of removing impurities from scandium chloride solution was proposed,which includes D370resin adsorbing Fe in high acidity,D851resin adsorbing Zr in medium acidity and D851resin adsorbing Sc at low acidity.Flow experimental results show that removal rates of Al,Ca,Fe,Zr,Ti and Si,were100%,99.6%,100%,100%,99.5%and100%respectively.

Scandium recovery from raffinate copper leach solution as potential new source with ion exchange method

Raffinate copper leach solution of the Iran Sarcheshmeh copper complex has up to 3 mg/L scandium(Sc),which is significantly better than many existing sources,making it a possible source for the recovery of Sc using the ion exchange method.Visual Minteq software was employed to ascertain the ionic species likely to be formed under operational conditions in the mine and for selecting the suitable ion exchange resin.The cationic resin thus chosen was employed statically with ions-bearing synthesized solutions and statically/dynamically for actual copper mining raffinate solution.Room temperature and pH of 1.5 showed the highest Sc adsorption.The dynamic tests established the full saturation of the resin at 450 BV of the raffinate solution flow.Using sodium carbonate for elution,desorption of Sc,Y and Ce from the resin during static elution tests at constant duration was higher than that of Fe,Al and Cu.The results from the dynamic tests followed similar trends for the priority and the extent of the elution process.Desorption results from specimens of dynamic tests show a 60:1 concentration ratio leading to a 186 mg/L Sc-rich solution.

In-situ transformation of Bi_2WO_6 to highly photoreactive Bi_2WO_6@Bi_2S_3 nanoplate via ion exchange

As a two dimensional(2D)visible‐light‐responsive semiconductor photocatalyst,the photoreactivity of Bi2WO6 is not high enough for practical application owing to its limited response to visible light and rapid recombination of photogenerated electron‐hole pairs.In this paper,2D core‐shell structured Bi2WO6@Bi2S3 nanoplates were prepared by calcination of a mixture of Bi2WO6(1.3 g)and a certain amount of Na2S·9H2O(0–3.0 g)at 350°C for 2 h.The reactivity of the resulting photocatalyst materials was evaluated by photocatalytic degradation of Brilliant Red X‐3B(X3B),an anionic dye,under visible light irradiation(?>420 nm).As the amount of Na2S·9H2O was increased from 0 to 1.5 g,the degradation rate constant of X3B sharply increased from 0.40×10?3 to 6.6×10?3 min?1.The enhanced photocatalytic activity of Bi2WO6@Bi2S3 was attributed to the photosensitization of Bi2S3,which greatly extended the light‐responsive range from the visible to the NIR,and the formation of a heterojunction,which retarded the recombination rate of photogenerated electron‐hole pairs.However,further increases in the amount of Na2S·9H2O(from 1.5 to 3.0 g)resulted in a decrease of the photocatalytic activity of the Bi2WO6@Bi2S3 nanoplates owing to the formation of a photo‐inactive NaBiS2 layer covering the Bi2WO6 surface.

Study on the permselectivity of ion exchange membrane

Ion exchange membranes with high permselectivity (the character of separatingcations from anions or anions from cations) and high selectivity (the character of separatingcations or anions of different valencies) are important for electrodialysis process. The Donnanequilibrium theory, based on the equilibrium of ions and no electric field, can not exactly explainthe permselectivity of ion exchange membrane for ED process, since it is impossible to set up a ionexchange equilibrium between membrane and solution and to neglect the influence of electricaldriving force on ions during ED process. A novel model named 'anti-electric potential' isestablished to interpret the permselectivity of ion exchange membrane, according to thedetermination of electric potential between membranes and the variation of elements content insolutions and membranes. The results of experiment prove that the 'anti-electric potential' reallyexists within membranes. As for the selectivity, the results reveal that electric potential andhydration energy have great influence on the concentration and mobility of ions in membranes.

Synthesis of Pb-Feldspar by Ion Exchange Reaction and Its Implications

Feldspar and Pb（NO3）2 were mixed and reacted at T=380℃ to synthesize Pb-feldspar. In the XRD （X-ray diffraction） pattern of the product, the d values （crystal lattice spacing） of the five peaks are 0.654, 0.342, 0.332, 0.327 and 0.257 nm. The XPS analysis results show that the binding energy of Pb 4f（7/2） in the feldspar was between 137.81-138.03 eV. Pb^2＋ can replace alkali and alkali earth cations in the feldspar structure through ion exchange reaction to form Pb-feldspar.

Structure and resistance of concentration polar layer on cation exchange membrane-solution interface

Membrane/solution interface consists of a neutral concentration polai layer(CPL) and a charge layer(CL) under external electrical field, and the neutral CPL can be neglected under high frequency AC electrical field. The relationship of CL thickness e with electrolyte concentration C and fixed ion exchange sites density σ in membrane surface layer can be expressed as e

Kinetic modeling of adsorption of vanadium and iron from acid solution through ion exchange resins

This study assessed the adsorption process and the reaction kinetics involved in the selective recovery of vanadium from an acid solution containing iron as an impurity.Four commercial resins were studied:Lewatit^(®)MonoPlus TP 209 XL,Lewatit^(®) TP 207,Dowex^(TM)M4195(chelating resin)and Lewatit^(®) MonoPlus S 200 H(strong cationic exchange resin).To investigate the effect of time on the adsorption process,batch experiments were carried out using the following initial conditions:pH 2.0,298 K,and a proportion of 1 g of resin to 50 mL of solution.The variation of pH over time was analyzed.Chelating resin released less H+ions as the adsorption occurred,resulting in a lower drop of pH when compared to S 200 H resin.Ion adsorption by the resins was also evaluated through FT-IR and SEM−EDS before and after the experiments.Among the evaluated kinetic models(pseudo-first order,pseudo-second order,Elovich and intraparticle diffusion models),the pseudo-second order model best fits the experimental data of the adsorption of vanadium and iron by all of the four resins.M4195 resin showed the highest recovery of vanadium and the lowest adsorption of iron.Kinetic data,which are fundamental to industrial processes applications,are provided.

Modelling of graded index waveguide fabricated by ion exchange on Er^(3+) doped glass

A general numerical tool, based on thermal diffusion equation and full-vectorial eigen-mode equation, has been presented for the systematic analysis of graded index channel waveguide fabricated by ion exchange on Er^3＋ doped glass. Finite difference method with full-vectorial formulation （FV-FDM） is applied to solving the full-vectorial modes of graded index channel waveguide for the first time. The coupled difference equations based on magnetic fields in FV-FDM are derived from the Taylor series expansion and accurate formulation of boundary conditions. Hybrid nature of vectorial guided modes for both pump （980 nm） and signal light （1550 nm） are demonstrated by the simulation. Results show that the fabrication parameters of ion exchange, such as channel opening width and time ratio of second step to first step in ion exchange, have large influence on the properties of waveguide. By optimizing the fabrication parameters, maintenance of monomode for signal light and improvement of the gain dynamics can be achieved in Er^3＋ doped waveguide amplifier （EDWA） fabricated by ion exchange technique. This theoretical model is significant for the design and fabrication of EDWA with ion exchange technique. Furthermore, a single polarization EDWA, which operates at wavelength from 1528 nm to 1541 nm for HE polarization, is numerically designed.