Phenol removal from aqueous solution by adsorption and ion exchange mechanisms onto polymeric resins

The removal of phenol from aqueous solution was evaluated by using a nonfunctionalized hyper-cross-linked polymer Macronet MN200 and two ion exchange resins, Dowex XZ (strong anion exchange resin) and AuRIX 100 (weak anion exchange). Equilibrium experimental data were fitted to the Langmuir and Freundlich isotherms at different pHs. The Langmuir model describes successfully the phenol removal onto the three resins. The extent of the phenol adsorption was affected by the pH of the solution; thus, the nonfunctionalized resin reported the maximum loading adsorption under acidic conditions, where the molecular phenol form predominates. In contrast both ion exchange resins reported the maximum removal under alkaline conditions where the phenolate may be removed by a combined effect of both adsorption and ion exchange mechanisms. A theoretical model proposed in the literature was used to fit the experimental data and a double contribution was observed from the parameters obtained by the model. Kinetic experiments under different initial phenol concentrations and under the best pH conditions observed in the equilibrium experiments were performed. Two different models were used to define the controlling mechanism of the overall adsorption process: the homogeneous particle diffusion model and the shell progressive model fit the kinetic experimental data and determined the resin phase mechanism as the rate-limiting diffusion for the phenol removal. Resins charged after the kinetic experiments were further eluted by different methods. Desorption of nonfunctionalized resin was achieved by using the solution (50% v/v) of methanol/water with a recovery close to 90%. In the case of the ion exchange resins the desorption process was performed at different pHs and considering the effect of the competitive ion Cl⁻. The desorption processes were controlled by the ion exchange mechanism for Dowex XZ and AuRIX 100 resins; thus, no significant effect for the addition of Cl⁻ under acidic conditions was observed, while under alkaline conditions the total recovery increased, specially for Dowex XZ resin.     

Uptake of iodine and bromine by ion-exchange resins in aqueous solution

The uptakes of molecular iodine and bromine by both strong acid cation (Dowex 50W-X4 and X8) and strong base anion (Dowex 1-X4 and X8) exchange resins have been studied in aqueous solutions at 25 degrees C. An empirical formula for the amount of solute taken up by the resin in mmol per gram of dry resin, Q, as a function of the solute concentration in M (mol dm(-3)), C, was derived. Direct proportional relationships between Q and C have been found, except for the bromine-anion exchanger system. In contrast to the cation-exchange resin, the anion exchanger exhibits extremely high affinity for I(2) and Br(2).     

Study on ion exchange equilibrium for some uni-univalent and uni-divalent reaction systems using strongly basic anion-exchange resin Duolite A-113

The study on thermodynamics of ion exchange equilibrium for uni-univalent Cl⁻/I⁻, Cl⁻/Br⁻, and uni-divalent Cl⁻/SO₄²⁻, Cl⁻/C₂O₄²⁻ reaction systems was carried out using ion-exchange resin Duolite A-113. The equilibrium constant K was calculated by taking into account the activity coefficient of ions both in solution as well as in the resin phase. The K values calculated for uni-univalent and uni-divalent anion exchange reaction systems were observed to increase with rise in temperature, indicating the endothermic exchange reactions having enthalpy values of 17.21, 36.60, 19.50, 18.43 kJ/mol respectively.     

Application of Br-82 as a radioactive tracer isotope to study bromide ion-isotopic exchange reaction in strongly basic anion exchange resin Duolite A-161

In the present investigation Br-82 radioactive isotope was used as a tracer to study the kinetics of exchange reaction taking place between the ion exchange resin and the external bromide ion solution. In an attempt to study the reversible bromide ion-isotopic exchange reaction kinetics, it was expected that whether the initial step was the exchange of radioactive bromide ions from the solution on to the ion exchange resin (forward reaction), or from the ion exchange resin in to the solution (reverse reaction), the two ion-isotopic exchange reactions should occur simultaneously, which was further confirmed from the values of specific reaction rate 0.122 and 0.123 min⁻¹ respectively obtained under identical experimental conditions. The radioactive tracer technique employed in the present investigation will be useful for characterization of various industrial grade ion exchange resins.     

Extraction and preconcentration of toxic metal ions from aqueous solution using benzothiazole-based chelating resins

Polystyrene-divinylbenzene resin (PS-DVB) was functionalized with a benzothiazole group. PS-DVB with amino group was initially prepared by nitration and reduction reactions and subsequently treated with ethyl 2-benzothiazolylacetate (BA) to obtain the chelating resin with an amide linkage (BA-PS-DVB). Meanwhile, the amino-PS-DVB was diazotized and coupled with BA to obtain the chelating resin with an azo linkage (azo-BA-PS-DVB). The resins were characterized by elemental analysis and infrared spectroscopy and evaluated for their extraction of Cd(II), Cu(II) and Pb(II) ions in water before their determinations by flame atomic absorption spectrometry (FAAS). Extraction conditions were optimized for batch method such as the pH of the solution, the extraction time and the adsorption isotherm. The optimum pH for the extraction of Cd(II), Cu(II) and Pb(II) are 8.0, 7.0 and 6.0, respectively, while the equilibrium time of all ions was reached within 10-20 min. The adsorption behavior of all the metal ions followed the Langmuir adsorption isotherm. In the column method, the optimum flow rates of metal sorption onto BA-PS-DVB and azo-BA-PS-DVB columns were 2.5 and 4.0 mL min^− 1. Metal ions sorbed onto columns were eluted by 0.5 to 2.0 M HNO₃. The preconcentration factors of Cd(II) and Cu(II) on azo-BA-PS-DVB and Cu(II) on BA-PS-DVB were 50, 50, and 20, respectively. The present column method gave acceptable validation results: 71.2 and 74.0% recovery for Cd(II) and Cu(II) and an overall relative standard deviation (R.S.D) less than 10% (n = 15). The proposed method was applicable for determining Cu(II) in drinking water.     

Preparation of ion exchange resins from carbonaceous adsorbents

Carbonaceous adsorbents are obtained by thermolysis of sulfonated macroreticular polystyrene ion exchange resins at 300-500°C. The hard, spherical, carbonaceous particles react exothermally with elemental chlorine to form products containing up to 38% Cl. The chlorinated particles react readily with polyamines to form anion exchange resins with capacities of up to 2.2 meq/g dry resin. Less than 60% of the nitrogen atoms in the particles are utilized as ion exchange sites. The carbonaceous particles can also be chloromethylated with chloromethyl methyl ether or chlorinated with sulfuryl chloride and then aminated with polyamines to form anion exchange resins, sulfonated with sulfuric acid or chlorosulfonic acid to form strongly acidic cation exchange resins, or chlorosulfonated and then aminated with polyamines to form anion exchange resins. Model structures of the thermolyzed resins containing polycyclic aromatic hydrocarbon fragments are proposed to explain their chemical reactivities.     

Aqueous-phase ion solvation and the selectivity of anion exchange resins for monovalent ions

This research examines and quantifies the influence of ion solvation parameters on the affinity of monovalent anions for strong-base anion resins. A data set comprising resin selectivity coefficients and solvation parameters from the literature is statistically analyzed using correlation and multiple regression techniques. The affinity of monovalent anions for the resin phase correlated well to ionic radii. Solvation parameters such as the hydration number, and entropy, enthalpy and free energy of hydration are also strongly correlated to selectivity. Using the stepwise regression procedure on subsets of independent variables, the entropy of hydration, which characterizes the structure-influencing nature of ions in solution, is incorporated as the sole parameter in the predictive model for resin selectivity. The data are best correlated by the exponential form of the regression equation, and the physical meaning of the correlation is shown to be reasonable. A simple rule for categorizing ions as structure-makers and structure-breakers is proposed, and the results are consistent with conventional classifications.     

Isotopic exchange between manganese hydroxide and manganese ions in aqueous solution

Heterogeneous isotopic exchange between manganese hydroxide and manganese ions in aqueous solutions tagged with radioactive⁵⁴Mn has been studied at different values of α, the ratio of the quantity of exchangeable ions in the solid phase to that in the liquid phase. The aging of the precipitate in its mother liquor prior to the exchange has a significant effect on both the extent and rate of the exchange reaction. A marked feature of great interest is the appearance of two aging-times, one at about 10² and the other at about 10⁴ min. The overall reaction appears to be of the consecutive type. In the case of a fresh precipitate, “complex-surface-exchange” and “self-diffusion” mechanisms are the most probable rate-determining steps in the initial and final stages of the reaction, respectively. “Complex-surface-exchange” is a new suggested mechanism. In the case of a well-aged precipitate, “surface-exchange” and ‘self-diffusion” mechanisms are the most probable-determining steps in the initial and final stages of the reaction, respectively.     

Study on a stable destruction method of radioactive waste ion exchange resins

This paper is a study on a stable destruction method of radioactive waste ion exchange resins. According to the resin TGA results, its decomposition occurred through three stages. And a sufficient retention time of the resins and an effective retention capacity of SO₂ gases and the doped metal compounds were required to destruct resins doped with radioactive metals stably. The resins doped with radioactive metal surrogates were effectively destructed in the lab-scale MCO system. CO and SO₂ emissions were below 100 and 1 ppm, respectively. And the surrogates were collected more than 99.9% in the molten carbonate. Thus, the resins can be destructed stably in the MCO process.     

Effect of bromide ion on the kinetics of bromination of o-hydroxy benzoic acid by bromine in aqueous solution

The kinetics of the bromination of o-hydroxy benzoic acid has been studied by rotating platinum electrode (RPE) technique. The bromide ion has been found to remarkably enhance the specific reaction rate. This is associated with a fall in energy of activation. The other added ions like nitrate, acetate and bicarbonate have shown that the base catalysis or salt effect is improbable. The mechanism suggested to explain the catalytic effect of bromide ions.     

Adsorption of strontium ions from aqueous solution on Pakistani coal

Summary The adsorption of strontium ions from aqueous solution on a Pakistani coal powder has been studied as a function of shaking time, amount of adsorbent, pH, and strontium ion concentration. Conditions for the maximum adsorption of strontium ions have been established. Results reveal that the diffusion of strontium ions into the pores of coal powder occurs during the adsorption process and intra-particle diffusion controls the kinetics of the process. The Langmuir and D-R adsorption equations are valid over the entire range of studied concentration. The influence of different anions on the adsorption of strontium ions was also studied.     

Water exchange dynamics of lithium(I) ion in aqueous solution

The water exchange dynamics of the fourfold coordinated first hydration shell of the lithium(I) ion was studied by both direct and umbrella sampling QM/MM-MD and classical MD simulations. The structural changes and energetics accompanying the activation process are discussed. The overall exchange rate constant was found to be k(ex) = 5.8 x 10(9) s(-1) from classical MD simulations. QM/MM-MD umbrella sampling simulations predict an exchange rate constant of k(TST) = 1.01 x 10(10) s(-1) as obtained from classical transition-state theory. First-shell ligands exchange preferably via an associatively activated mode.     

On the distribution coefficient of nickel dimethylglyoximate between an aqueous solution and organic solvents

The distribution coefficients of nickel dimethylglyoximate between an aqueous solution and 6 inert solvents were determined at 20°. The distribution coefficients of the nickel chelate were quantitatively interpreted in terms of solubility parameters. The solubility parameter for the nickel chelate was evaluated to be 12.9, that for the aqueous solution to be 18.6, and the molar volume of the chelate to be 182 ml/mol.     

Competitive adsorption of uranium(VI) and thorium(IV) ions from aqueous solution using triphosphate-crosslinked magnetic chitosan resins

The triphosphate-crosslinked magnetic chitosan resins (TPP-MCR) with a diameter range of 200–350 nm were synthesized for the adsorption of U(VI) and Th(IV) ions from aqueous solutions. The adsorption experiments were conducted in both mono-component systems with pure actinide solution and bi-component systems with different U/Th mass ratios. The maximum adsorption capacities in mono-component systems determined by Langmuir model were 169.5 and 146.8 mg g^?1 for U(VI) and Th(IV), respectively. In bi-component systems, U(VI) and Th(IV) adsorption capacities were reduced significantly, and the combined sorption capacities were substantially lower (almost halved) compared to those obtained by the addition of sorption capacities using mono-component solutions, indicating that U(VI) and Th(IV) compete for the same sorption sites. Adsorption–desorption experiments for five cycles illustrated the feasibility of the repeated use of TPP-MCR for the adsorption of U(VI) and Th(IV) ions.     

Purification of aqueous glyoxal from organic acids by ion exchange

A procedure for the purification of aqueous glyoxal (obtained by the partial oxidation of glycol) from carboxylic acids was described. Mono- and dibasic organic acids can be removed from solution without any substantial losses of glyoxal by using weakly basic EDE-10P and AN-31 anionites. A mechanism of the adsorption of carboxylic acids on weak resins was suggested based on the IR spectra recorded in a study of AN-31 anion-exchange resin. Using this method of purification also allowed the removal of the glyoxal condensation products from solution.     

Adsorption equilibrium and heat of phenol onto aminated polymeric resins from aqueous solution

Aminated polystyrene resins (NDA-101 and NDA-103) were synthesized, and their adsorption performances for phenol in aqueous solution were investigated and compared with the commercial polystyrene resin (Amberlite XAD-4) and weakly basic polystyrene resin (Amberlite IRA-96). All the associated adsorption isotherms are well described by Freundlich and Langmuir equations. The results indicated that all the four resins spontaneously adsorb phenol driven mainly by enthalpy change, and their adsorption capacities, free energy changes, enthalpy changes, and entropy changes for phenol followed the same order as: NDA-101 > NDA-103 > XAD-4 > IRA-96. Surface energy heterogeneity analysis by Do's model also suggested that the surfaces of XAD-4 and IRA-96 were more homogeneous, and the better adsorption capacity and affinity of the aminated resins (NDA-101 and NDA-103) are probably due to their multiple hydrogen bonding and π–π stacking interactions with phenol molecule.     

Comparison of isotherms for the ion exchange of Pb(II) from aqueous solution onto homoionic clinoptilolite

The ion exchange equilibrium of Pb(II) on clinoptilolite modified with NH(4)Cl and NaCl can be represented by two types of isotherms. The first one is the ion exchange isotherm based upon the constant of thermodynamic equilibrium for the ion exchange reaction; however, the fitting procedure for this isotherm can be very tedious due to all the calculations involved and additional thermodynamic data. The second one is the Langmuir isotherm. The use of the Langmuir isotherm to represent ion exchange equilibrium has increased in recent last years since it adequately fits the equilibrium data and, furthermore, its calculation is much simpler. A comparison between the two isotherms showed that they fitted the experimental data reasonably well, but the Langmuir isotherm is much simpler and easier to use.