Ion-Exchange Studies in the Removal of Polybasic Acids. Anomalous Sorption Behavior of Phosphoric Acid on Weak Base Resins

Abstract

Sorption behavior of phosphoric acid on the weak base resins Amberlite IRA-93 and Dowex WGR-2 is reported. Studies on sorption equilibria and dynamics reveal anomalous sorption behavior as compared to sorption of strong and weak monobasic acids. A mathematical treatment is developed to correlate the experimental data on sorption dynamics. An alternative type of mechanism is also proposed based on the results obtained in this work to explain the anomalous sorption behavior of phosphoric acid on weak base resins.     

Modified Shrinking Core Model for Reversible Sorption on Ion-Exchange Resins

Abstract

A modified shrinking core model is proposed to correlate dynamics of acid sorption on weak base ion-exchange resins in free base form. The model considers reversibility of the sorption process which is ignored in the conventional shrinking core model. The model is easy to apply and is shown to yield results which are in agreement with a computationally intensive rigorous model. The model is successfully verified using the experimental data on sorption of strong acids (HCl and HNO₃) on weak base resins (Dowex WGR-2 and Amberlite IRA-93).     

Nanofiltration modeling: the role of dielectric exclusion in membrane characterization

A general model is presented, called Donnan steric pore model & dielectric exclusion (DSPM&DE) to describe mass transfer of electrolytes and neutral solutes through nanofiltration membranes. The transport equations of ions through the membrane are based on the extended Nernst-Planck equation, accounting for ionic diffusion, electromigration and convection in the membrane pores; the hindered nature of diffusion and convection of the species inside the membrane is considered. Ionic partitioning at the interfaces between the membrane and the external phases takes into account of three separation mechanisms: steric hindrance, Donnan equilibrium and dielectric exclusion. The role of the difference existing between the dielectric constant of the aqueous solution in the pores and the dielectric constant of the membrane material is assumed dominant in determining the rejection mechanism related to the dielectric effects. The membrane is characterized through the use of adjustable parameters such as the average pore radius, the effective membrane thickness and the volumetric charge density.A general assessment is presented for membrane characterization. A new procedure is introduced for the membrane parameters calculation, based on a simple analytical relationship developed to describe rejection of single symmetric electrolytes.Two versions of the DSPM&DE model are presented, in which the “integral” model is a weak simplification of the general “differential” model. The validity of the models presented is fully demonstrated in the case of negatively charged membranes, through the comparison with experimental results performed in a wide range of operative conditions. The separation effect related to the dielectric exclusion is relevant with respect to Donnan equilibrium in determining bivalent counter-ions rejection, such as CaCl₂ as well as MgSO₄, whereas dielectric effects are not so remarkable in the case of mixtures containing various co-ions, such as NaCl+Na₂SO₄.     

Diffusion of Aggressive Media in Hydrophilic Polymers

Abstract

The simultaneous sorption and diffusion of acid and salt in polyvinylalcohol are considered under conditions of polymer swelling. Obtained data on water sorption by PVA show an anomalous mechanism of the transport of solvent in this kind of polymer. The analysis of equilibrium sorption of an acid-salt mixture shows that interactions of polymer OH groups with hydrogen ions of hydrogen chloride lead to a decrease in salt solubility in the polymer. The theory of Donnan equilibrium was used to solve the problem of the sorption of the acid-salt mixture as well as to create the boundary conditions for a proposed mathematical model of the transport of the buffer mixture.

Methods of determining parameters of the buffer mixture transport in hydrophilic polymers have been created and physicochemical characteristics of investigated multicomponent system are calculated on the basis on these methods.     

Absence of Donnan Exclusion at High‐Concentration Ion Exchange for Macroporous Anionic Resin

Abstract

High‐concentration ion exchange has been studied for an anionic macroporous resin. The mechanism of interaction of Lewatit MP‐500 (strong base resin) with several high‐concentration inorganic salts was analyzed in order to determine the effect of the Donnan potential in the process.

The systems under study were Cl^?, SO₄ ^2? as counter‐ions and K⁺, Na⁺ as co‐ions in different combinations as single electrolytes. These salts were chosen because of their interest as raw materials in the fertilizer industry. The study focuses mainly on the behavior of high‐concentration (over 1 M) counter‐ and co‐ions in the anionic resin. The results showed that Donnan exclusion does not take place completely and that electrolyte penetration inside the resin is observed. Furthermore, a certain amount of ion exchange was observed for the co‐ions (K⁺ and Na⁺) when the resin was presaturated with sulphate and chlorides that were present in the solution. Equilibrium and kinetics data were obtained under these special experimental conditions. Equilibrium constants were obtained for counter‐ions and adsorption constants for co‐ions using a constant separation factor isotherm, while diffusion coefficients were obtained using a pore diffusion model.     

Sorption and diffusion of weak acids in nylon—dual sorption and diffusion model

The sorption and diffusion of fluoro-substituted acetic acids in nylon-6 were measured. Hydrochloric acid was also used for comparison purposes. The results were successfully interpreted quantitatively by a dual sorption model, namely by contribution of associated and dissociated species of the acids concerned. As was expected in the case of the sorption of the weakest acid among the acids used, acetic acid, the contribution of associated species is large. The analysis of the diffusion behavior of acetic acid has shown that the contribution of associated species plays a dominant role in the diffusion process in nylon.     

THE SORPTIONBEHAVIOR OF BORIC ACID ONWEAK-BASE ANIONEXCHANGE RESIN

The sorption isotherns of boric acid on WA-21 weak-base anion exchange resin and the sorption band shape as veil as its migration velocity in a four-inch diameter ion-exchange column were studied.

The isothems show S-shapes with gentle slope at both low concentration and high concentration regions. In the band migration study, it has been found that these S-shaped isotherns affected the velocities of the peak maximum as the band migrated along the column. The velocities could be calculated with the simple solute movement equation. These results suggest that sorption of nolecular species, rather than ion exchange of the counter ions is the main process that occurs inside the pores of a weak-base ion-exchange resin which is in contact with a very weak electrolytic solution, such as that of boric acid.     

Adsorption equilibrium and kinetics studies of divalent manganese from phosphoric acid solution by using cationic exchange resin

There are numerous impurities in wet-process phosphoric acid, among which manganese is one of detrimental metallic impurities, and it causes striking negative effects on the industrial phosphoric acid production and downstream commodity. This article investigated the adsorption behavior of manganese from phosphoric acid employing Sinco-430 cationic ion-exchange resin. Resorting FT-IR and XPS characterizations, the adsorption mechanism was proved to be that manganese was combined with sulfonic acid group. Several crucial parameters such as temperature, phosphoric acid content and resin dose were studied to optimize adsorption efficiency. Through optimization, removal percentage and sorption capacity of manganese reached 53.12 wt%, 28.34 mg·g⁻¹, respectively. Pseudo-2nd-order kinetic model simulated kinetics data best and the activation energy was evaluated as 6.34 kJ·mol⁻¹ for the sorption reaction of manganese. In addition, the global adsorption rate was first controlled by film diffusion process and second determined by pore diffusion process. It was found that the resin could adsorb up to 50.24 mg·g⁻¹ for manganese. Equilibrium studies showed that Toth adsorption isotherm model fitted best, followed by Temkin and Langmuir adsorption isotherm models. Thermodynamic analysis showed that manganese adsorption was an endothermic process with enhanced randomness and spontaneity.     

KINETICS OF CADMIUM ION SORPTION ON ION EXCHANGE AND CHELATING RESINS

ABSTRACT

Cadmium sorption from aqueous solutions on sulfonic (C-150) and iminodiacetic (S-930) Purolite macroporous resins was investigated. The influence of operating variables such as initial pH, Cd(H) concentration, time and temperature on the equilibrium parameters was measured. The ion preference and sorption ability of resins, i.e. binding constant (b) and saturation capacity {x_m), derived from sorption isotherm, depend on the functional group structure. The Cd(II) uptake is only particle diffusion controlled. The kinetic parameters, i.e. t_1/2 values for 50 % attainment of equilibrium sorption, rate constant (K¯ ) and diffusion coefficient (D¯) are higher on the sulfonic resin. The “moving boundary” particle diffusion model fits the entire ion sorption process on chelating resin, but only the initial sorption on the sulfonic resin, confirming the difference in chemistry between chelation and ion exchange.     

Adsorption equilibrium and kinetics studies of divalent manganese from phosphoric acid solution by using cationic exchange resin

There are numerous impurities in wet-process phosphoric acid, among which manganese is one of detrimental metallic impurities, and it causes striking negative effects on the industrial phosphoric acid production and downstream commodity. This article investigated the adsorption behavior of manganese from phosphoric acid employing Sinco-430 cationic ion-exchange resin. Resorting FT-IR and XPS characterizations, the adsorption mechanism was proved to be that manganese was combined with sulfonic acid group. Several crucial parameters such as temperature, phosphoric acid content and resin dose were studied to optimize adsorption efficiency. Through optimization, removal percentage and sorption capacity of manganese reached 53.12 wt%, 28.34 mg·g^-1, respectively. Pseudo-2nd-order kinetic model simulated kinetics data best and the activation energy was evaluated as 6.34 kJ·mol^-1 for the sorption reaction of manganese. In addition, the global adsorption rate was first controlled by film diffusion process and second determined by pore diffusion process. It was found that the resin could adsorb up to 50.24 mg·g^-1 for manganese. Equilibrium studies showed that Toth adsorption isotherm model fitted best, followed by Temkin and Langmuir adsorption isotherm models. Thermodynamic analysis showed that manganese adsorption was an endothermic process with enhanced randomness and spontaneity.     

OXIDATIVE TREATMENT FOR THE PREVENTION OF CHROMIUM ACCUMULATION IN A POLYMERIC MATRIX

ABSTRACT

Chromium (III) species tend to accumulate in the organic matrix with carboxylic groups like weak acid ion exchanger resins. Using conventional acidic solutions, chromium (III) can be partially eluted in some circumstances, while an oxidative stripping using hydrogen peroxide in alkaline media seems to be useful. Previously, Cr(III)–H₂O₂ reaction has been studied in aqueous solutions (homogeneous system) at 20°C, testing for 0.5, 1.0 and 2.0?mM of Cr(III) as total metal concentration. The effect of hydroxide ion on the rate of oxidation was also examined. Chromate was continuously monitored using an FIA system. The general mechanism of the homogeneous reactions has been postulated and the main kinetic parameters of the reactions have been calculated. Ageing of chromium (III) solutions has an important effect on the experimental results. Metal elution from cationic resin is usually carried out by strong acids, but here chromium loaded onto a cation-exchange resin is completely stripped after oxidation to chromate ion. The reaction rate is mainly controlled by intraparticular diffusion of the anionic species through the cationic resin. Surprisingly, these are not rejected from the resin phase by the Donnan exclusion. This apparently anomalous behaviour has been explained in terms of the reaction mechanism.     

Ion-Exchange Kinetics for the Removal of Potassium from Crude Polyols on Strong Acid Resins

Abstract

Batch dynamics for the uptake of potassium from crude polyols on Amberlite 252, a strong acid ion-exchange resin, are obtained over a wide range of conditions. Experimental data have been analyzed using a homogeneous model with finite solution volume. An increase of diffusion coefficients with the resin weight used in the purification is observed. An asymptotic maximum value, approaching the value of the diffusion coefficient in bulk solution, is reached for high resin weights or low values of external concentration. The heterogeneous nature of the resin matrix and the large size of the diffusing molecule is proposed as an explanation of this behavior. The proposed purification procedure finds general applicability for other polyol types, being economically and technically feasible.     

Shale Oil Denitrogenation with Ion Exchange

Abstract

The nitrogen-containing aromatics normally found in crude retorted shale oils have been shown to be involved in reactions leading to the deposition of insoluble gums and sediments. These nitrogen-containing compounds must be removed in order to permit the effective utilization of the shale oil product.

A process is proposed in which the nitrogen-containing compounds found in raw shale oil are removed by mild hydrodenitrogenation followed by resin ion exchange. Ion exchange data from experimentation involving six jet fuel (15M-271°C) and diesel fuel (271–343°C) boiling point cuts are presented. Amberlyst A-15, a macroreticular, strongly acidic, cation exchange resin is used in this study. Three types of experiments were performed: batch sorption equilibrium experiments, batch sorption kinetics experiments, and dynamic ion-exchange column performance tests. The Langmuir isotherm was found to describe the equilibrium sorption behavior of the shale oil/ion-exchange resin system fairly Well. The sorption kinetics are described using a quadratic-driving force model.     

Sorption of Aromatic Amines on a New Ligand Exchanger of Sporopollenin-Bound Co2+ Ion

Abstract

The mechanism of ligand-exchange sorption of aromatic amines such as p-chloroaniline, p-toluidine, and p-nitroaniline as ligands on a Co²⁺-loaded ligand exchanger has been studied. The observed rate seems to be related to the rate of ligand sorption with the mobile phase and pH in the aqueous phase. The saturation capacity and binding constant of ligand sorption on the resin increase with increasing basicity of amines. The rate of attainment of equilibrium sorption of aromatic amines is seen to be nearly similar. Coupled with the fact that different concentrations of solution were employed, these results may be interpreted as indicating that particle diffusion is the rate-controlling step. On the contrary, film diffusion was not rate-controlling step in the ligand sorption process under the conditions employed. It is shown that the kinetic parameters measured in single component experiments provide good prediction behavior. The pH dependencies and sorption isotherms of aromatic amines on the resins were also studied.     

Sorption of cobalt to bone char: Kinetics, competitive sorption and mechanism

Swine bone char is the combustion residues of swine bone. Cobalt adsorption to swine bone char was studied. Batch kinetics studies showed that a rapid uptake occurred during the first 5 min and was followed with a very slow intraparticle diffusion process. The sorption kinetics was ideally conformed to pseudo-second equation, indicating several mechanisms involved in the adsorption process. Equilibrium sorption isotherm studies showed that the Freundlich isotherm model satisfactorily described the sorption data. The presence of co-ions had appreciable inhibiting effects on cobalt uptake by bone char because copper and zinc had higher affinity for the bone char surface than cobalt. Calcium concentration in solution and XRD analysis showed that ion exchange was involved in the removal of Co from solution over a certain initial cobalt concentration range.     

Separation of Carboxylic Acids from Carboxylates by Diffusion Dialysis

Abstract

Acetic acid/sodium acetate and propionic acid/sodium propionate were separated by the diffusion dialysis technique using Neosepta AFN‐7 and Selemion DSV membranes. Accounting for molarities of carboxylic acids and salts in broths produced by the pH controlled bacterial fermentation (pH 4–6), the experiments were carried out with carboxylates in excess of acids. The sorption equilibria established for acetic acid, propionic acid, and the sodium salts of both acids (single solute experiments) revealed a high sorption of acids in both membranes and the rejection of carboxylates. The partition coefficients were found to be from unity up to 2 for the acids and 0.04–0.05 for the salts. Reflecting a high sorption, the fluxes for the acids amounted from 1.5 to 2.0 mol · m^?2 · h^?1 and only 0.07–0.08 mol · m^?2 · h^?1 for the salts (one molar solutions). The separation factors computed upon the experiments performed with the ternary solutions were found between 20 to 37 for the Neosepta AFN‐7 membrane and about 29 for the Selemion DSV membrane. Accounting additionally, for the results of the separation of lactic acid from sodium lactate reported in our earlier paper the results prove the diffusion dialysis to be applicable to the separation of mean strength and weak carboxylic acids from their salts.     

Evaluation of the sorption of metal ions on a complexing resin from different solutions based on the Gibbs–Donnan model

The intrinsic protonation and complexation constants of an ion-exchange complexing resin, previously determined in condition of trace metal ions on the basis of the Gibbs–Donnan model of ion-exchange resins, were here used to evaluate the concentration of metal ions sorbed on the resin when the metal ion is in excess. The resin considered was a commercial one, containing carboxylic groups at a concentration of 10 mmol g⁻¹ of dry resin. Metal ions complexable by the active groups present in the resin phase, i.e. alkaline earth metals and cadmium(II), were investigated, together with a not complexable metal ion, sodium, which enters in the resin phase only by diffusion and ion-exchange. The calculation method is an iterative one, taking into account the diffusion and ion-exchange in the case of the not complexable metals, and the complexation in the case of the complexable metal ions. The concentration of metals in the resin phase calculated by the proposed procedure was compared with that obtained experimentally in some representative solutions at different composition and acidity. The agreement was acceptable, showing that the intrinsic complexation constants are of help not only in conditions of trace metal, but also for evaluations at completely different conditions. In the case of complexable metal ions it was shown that the complexation in the resin phase is the most important sorption mechanism, even if ion-exchange takes place at high acidity, when the complexation is negligible.     

Diffusion of m-sulfobenzoic acid in nylon 6

Diffusion of m-sulfobenzoic acid in nylon 6 was measured by using the S-35 labelled acid as a tracer. A multimodal mechanism, identical to that in a preceding paper on sorption, was assumed, according to which the protonated acid diffused by dissolution, and the two dissociated acids diffused by competitive interaction with the charged sites in nylon 6. The concentration dependence of the diffusion coefficients was explained by the chemical potential gradient model. The monobasically dissociated species was found to be dominant in the diffusion process. Diffusion coefficients and the activation energies of diffusion did not vary significantly with pH.     

Arsenate and Dichromate Removal Efficiency of a New Calix[4]arene Impregnated Resin

This article highlights a newly synthesized 5,11,17,23-tetra-tert.butyl-25,26,27,28-tetrakis(hydrazidecarbonylmethoxy)-calix[4]arene (3) impregnated resin 4 and it's sorption ability for the removal of selected oxoanions, i.e., (arsenate and dichromate) from aqueous environment. Resin 4 was characterized by using FT-IR spectroscopy, scanning electron microscope (SEM), elemental, and thermogravimetic (TGA) analyses techniques. Sorption study was carried out through static and dynamic methods with continuous flow operation to evaluate the potency of resin 4 under various conditions. Several parameters, such as effect of sorbent dosage, contact time, pH, and initial concentration were optimized through batch experiments. Results justify that % sorption of these oxoanions is highly dependent on pH of the solution. Equilibrium was achieved in 45 min, while sorption efficiency of resin 4 can be better explained by Langmuir and Temkin isotherm models. Furthermore, kinetically both oxoanions follow pseudo second order model. Additionally, sorption of arsenate more appropriately could be explained by Moris-Weber diffusion kinetic model. For the dynamic method, Thomas model was used to calculate the kinetic coefficient (k_TH) and maximum sorption capacity (q_o) of resin 4 which are 3.84 and 5.94 ml mg^?1 min^?1 and 0.185, 0.160 mg g^?1 for As (V) and Cr (VI) respectively. Furthermore, resin 4 has been found as potential sorbent for removal of these oxoanions from contaminated surface water samples.     

A Model Predicting Equilibrium for Plutonium Sorption by Anion Exchange Resin

A mathematical model is derived for prediction of equilibrium between plutonium in aqueous solution and plutonium sorbed on anion exchange resin. The model is analogous to the Langmuir (BET Type I) model for adsorption. Sorption kinetics are modeled as a first order reaction with respect to the plutonium and the resin sorption site concentrations. The model predictions are correlated to previously reported experimental equilibrium data over a range of plutonium concentration from 0.0029 to 300 g Pu/L. Plutonium content of the resin pores is shown to be a significant portion of the total resin phase plutonium. Two methods are described for calculating resin porosity from experimental equilibrium data. The porosity of Dowex-1x4 resin in 7M nitric acid is calculated to be 5 to 8 vol% at high plutonium sorption. Maximum sorption capacity of the resin for plutonium is calculated to be from 87 to 93% of the stoichiometric capacity for a divalent anion.