Exchange Isotherms Research Articles

Effect of temperature on ion exchange equilibrium between AMX membrane and binary systems of Cl-, NO-3 and SO2-4 ions

The effect of the temperature variation on ion exchange equilibrium between an anion exchange membrane and solutions of electrolytes containing the most dominant anions of natural waters (CI−, NO− 3 and SO2minus; 4) was studied. All experiments were carried out at 0.3 mol l−1. AMX membrane experimented in this work is a commercial product provided by TOKUYAMA SODA. Humidity percentage and ion exchange capacity were determined. Ionic exchange isotherms for the binary systems (CI−/NO−)3,(CI−/SO2− 4) and (NO− 3 / SO2− 4) were established at different temperatures from 283 to 313 K. At 283 and 298 K, the affinity order was: CI− > NO− 3 > SO2− 4. This order was NO− 3 > CI− > SO2− 4 at 313 K. Selectivity coefficients Kj i and thermodynamic equilibrium constants K0j i calculated for uni-univalent and uni-bivalent ions exchange reaction system increase with increasing temperature. Thermodynamic parameters such as standard free enthalpy change, standard enthalpy change, and standard entropy change were calculated....

Isotherm of Pb-Na cation exchange on iron-manganese concretions

Isotherm of Pb2+ and Na2+ cation exchange on iron-manganese concretions was studied. The ion exchange was described by a modified Langmuir equations. The limiting sorption and apparent ion-exchange constant were calculated.

Effect of ionic strength on ion exchange equilibrium between cationic membranes and K+/Na+, K+/Li+ and Na+/Li+ binary systems

Ion exchange membranes are receiving considerable attention and are successfully applied for desalination and for treating industrial effl uents. They are effi cient tools for the concentration or separation of food and pharmaceutical products containing ionic species. Extensive work has been reported on synthesis, characterization, properties and applications of these membranes. In this work ion exchange isotherms for the binary Na+/K+, Li+/K+, and Li+/Na+ were established at various ionic strengths, using CRP cationic membrane. All experiments were carried at 25°C, by setting the ionic strength in the range of I = 0.1–1.5 mol · l–1. All the results given by this membrane were compared with those obtained, in the same conditions, with CMX membrane. For the two membranes, up to ionic strength 1.5 mol · 11 affinity order was: KK+ > Na+ > Li+. Selectivity coefficients KK+ Na+ KK+ Li+ KNa+ Li+ for homogenous CMX membrane were greater than those determined for heterogeneous CRP membrane. For low ionic strength till I = 0.2 mol · 11,these selectivity coefficients decrease strongly and tend asymptotically to unity for higher values of I. The product of selectivity coefficients KNa+ Li+ · KK+ Na+ · KLi+ K+ were always close to unity.

ChemInform Abstract: Thermodynamic Treatment of H+/Sr2+ Ion-Exchange in γ-Titanium Phosphate

Abstract The H + /Sr 2+ ion-exchange in γ-Ti(HPO 4 ) 2 · 2H 2 O was studied. Exchange isotherms and pH curves were obtained at 298.15, 313.15 and 328.15(± 0.1) K. The half-exchanged phase TiHSr 0.5 (PO 4 ) 2 · 3H 2 O (interlayer distance 1.34 nm) was detected. The equilibrium constants and the standard molar Gibbs free energy, enthalpy and entropy of the exchange reaction were determined.

Synthesis and characterisation of mesoporous silica phases containing heteroatoms, and their cation exchange properties. Part 5: Cation exchange isotherms, and the measurement of radioisotope distribution coefficients, for an MCM-22 phase containing aluminium

Cation exchange isotherms were constructed for the replacement of Na cations by Li, K, Rb, Cs, NH 4, Mg, Ca, Sr, Ba, and Al from a well characterised MCM-22 phase which contained aluminium as a heteroatom. Thermodynamic assessment of the isotherms enabled the construction of a selectivity series. Comparisons, including standard free energy values, have been drawn to similar results measured for other MCM-41 phases and some high-silica zeolites. This work additionally describes studies on the MCM-22 phase to examine its potential ability to scavenge radioisotopes from various solutions as simulants of those found in nuclear waste. The isotopes studied were 241-Am, relevant to spent nuclear fuel, and 137-Cs, 57-Co, 51-Cr, 59-Fe, 54-Mn, 89-Sr, 65-Zn present in nuclear wastes as fission products, from neutron activation in nuclear installations, and arising from medical uses. Measurement of distribution coefficients enabled the construction of selectivity series which demonstrated the versatility of the phases to scavenge specific isotopes.

Heterovalent cation exchange in two savanna soils of different lithogenic origin as described by the Rothmund–Kornfeld model

Prediction of cation selectivity is imperative for soil fertility management and disposal of metal-polluted wastes through the land. Predictive thermodynamic approaches based on the Vanselow–Argesinger and Gaines and Thomas conventions require complex expressions. We examined the two-parameter Rothmund–Kornfeld model for accessing thermodynamic equilibrium constant ( K ex) for K → Ca and K → Mg exchange in two soils formed on Basement Complex (BC) rocks and sandstones (SST) in the Nigerian savanna. The K ex values based on Vanselow–Argesinger convention for K → Mg exchange (0.112–0.182 mol kg − 1 ) and K → Ca exchange (0.069–0.103 mol kg − 1 ) were in close agreement with Gaines and Thomas convention (0.115–0.183 mol kg − 1 for K → Mg and 0.072–0.103 mol kg − 1 for K → Ca exchange). Applying the Rothmund–Kornfeld approach to either Vanselow–Argesinger or Gaines and Thomas convention gave K ex values close to those based on classical Vanselow–Argesinger approach (0.130–0.156 mol kg − 1 for K → Mg and 0.075–0.106 mol kg − 1 for K → Ca) and the Gaines and Thomas convention (0.134–0.146 mol kg − 1 for K → Mg and 0.082–0.144 mol kg − 1 for K → Ca exchange). Regardless of lithology, the Rothmund–Kornfeld model sufficiently represented the K → Mg and K → Ca exchange isotherms of the soils, and its two parameters adequately predicted equilibrium exchange constant. Evidence from K ex and the positive change in free energy of exchange (Δ G ex o) indicated non-preference for Ca 2+ and Mg 2+ to K + in both soils, suggesting prediction of cationic selectivity and fertility can be extrapolated from one soil to the other in the savanna.

Multivariate Statistical Analysis of Potassium Status in Agricultural Soils in Hamadan, Western Iran

Multivariate statistical technique was used to determine the potassium (K +) status and to assess soil fertility and K leaching potential in some calcareous soils. Water-soluble K + (H 2O-K) and ammonium acetate-extractable K + (NH 4OAc-K) ranged from 0.019 to 0.590 (mean value 0.095) and 0.390 to 3.320 (mean value 0.954) cmol c kg −1, respectively. The nitric acid-extractable K + (HNO 3-K) varied from 1.03 to 13.63 (mean value 5.37) cmol c kg −1. The proportion of H 2O-K ranged from 0.34% to 14.8% of HNO 3-K, and 2.2% to 53.2% of NH 4OAc-K. The proportion of NH 4OAc-K ranged from 5.8% to 80% of HNO 3-K (mean value 23% of HNO 3-K). The tendency of the soil to lose K + by leaching was examined by determining K +-Ca 2+ exchange isotherms. The soils mostly had moderate to high values of K + sorption capacity, ranging from 10% to 58% (mean value 28%) of added K +. The Gapon coefficient varied widely from 1.1 to 12.0 (L mol −1) −1/2. Clay minerals were dominated by illite, smectites and vermiculite with small amounts of kaolinite. Principal component analysis (PCA) showed that the first four components accounted for 27.7%, 21.4%, 13.8%, and 8.9% of total variation, respectively. The non-hierarchical cluster analysis ( k-means clustering) grouped 75 sampling sites into six clusters, based on the similarity of soil quality characteristics. The results suggested that such classes could form a basis for variable-rate application to maintain an adequate K + status for crop production and to reduce potential K + loss from soil by leaching.

Predicting potassium fertilizer requirement using exchange isotherm approach in relation to soil characteristics

Determining potassium (K) fertilizer requirement using sorption isotherms is considered more accurate than conventional soil K tests. A total of 59 surface soil samples were used to establish K exchange isotherm. To evaluate K requirement sorption test, a glasshouse experiment using perennial ryegrass (Lolium perenne, cv. Roper) was carried out on 10 soil samples. The experiment was laid out as a completely randomized design with four replications and four K levels (K0, K20, K40, K80). Concentrations of K in solution established by adding K in the pots estimated from the sorption curve ranged from 20 to 80 mg K l−1 including check treatment (no K). Dry matter yield of ryegrass in most soils approached maximum as adjusted K levels were increased to 20 mg K l−1. The amounts of K required to bring the soils to 20 mg l−1 in soil solution varied among soils and ranged from 99 to 399 mg kg−1, on average 205 mg kg−1 soil. It was found that a useful regression model for the prediction of standard K requirement (K20) included the combination of plant available K extracted by NH4OAc (Av-K) and clay content: K20 = −41 − 0.63 Av-K + 9.0 Clay (R2 = 0.61, p < 0.001, n = 59).

Contribution of apoplast and symplast to short term nickel uptake by maize and Leptoplax emarginata roots

To characterize the complete Ni root sink over the short term, the contributions of apoplast and symplast to the metal root uptake were measured for both maize and the Ni hyperaccumulator Leptoplax emarginata, using a physico-chemical fractionation of root Ni after exposure. The apoplastic uptake accounted for 81.3–88.0% and for 90.6–95.5% of the total root uptake of maize and leptoplax, respectively. This could be modelled using exchange isotherms, such as the Langmuir or Freundlich isotherms. Root cell walls of both plant species showed similar affinity to Ni, although the hyperaccumulator had a higher apoplastic uptake. For maize as for leptoplax, the symplastic influx fitted a Michaelis–Menten function with similar K m and I max values, although the two plant species have contrasting abilities to accumulate Ni. This suggests that symplastic uptake is not the main factor of hyperaccumulation and that the Ni transport system might be similar in these two plants species. More research is needed to understand how the high level of Ni adsorption on root apoplast might affect the overall Ni uptake.

Synthesis and characterisation of mesoporous silica phases containing heteroatoms, and their cation exchange properties. Part 2. Cation exchange isotherms for MCM-41 phases

Well characterised MCM phases containing aluminium and zinc heteroatoms were selected from those described in Part 1 [A. Dyer, J. Newton, M. Pillinger, Micropor. Mesopor. Mater. (2009), doi:10.1016/j.micromeso.2009.06.002] to this series. Cation exchange isotherms were constructed for the replacement of Na cations from the solid phases by Li, K, Rb, Cs, NH 4, Mg, Ca, Sr, Ba, and Al cations. Thermodynamic assessment of the isotherms enabled selectivity series to be drawn up. Comparisons have been drawn to similar results measured for high-silica zeolites. These included standard free energy values.

Selectivity of Co and Ni by K-depleted micas

AbstractContamination of the environment with heavy metals, including cationic radionuclides, is a serious problem which has yet to be fully overcome. A class of potentially effective cation exchangers for sequestering heavy metals which has received little attention is K-depleted mica. The purpose of this study was to investigate the heavy-metal cation exchange properties of K-depleted phlogopite and biotite, which were prepared from a natural phlogopite and biotite, respectively, using sodium tetraphenylborate (NaTPB). The X-ray diffraction (XRD) patterns showed that interlayer K+ ions were completely replaced with exchangeable Na+ ions, resulting in the expansion of the d001 spacing of both K-depleted phlogopite and K-depleted biotite. In order to investigate the cation exchange selectivity of K-depleted phlogopite and biotite for Co2+ and Ni2+, cation exchange isotherms and Kielland plots were constructed. The isotherms and Kielland plots indicated that both K-depleted phlogopite and biotite are highly selective for Co2+ as well as Ni2+. The XRD patterns after both 2Na+ → Co2+ and Ni2+ exchange reactions suggest that double sheets of interlayer water are present in the interlayer. These K-depleted micas are potential cation exchange materials for removal of some heavy metals such as Ni and radioactive species such as 60Co from solution.

Cation Exchange Selectivity Coefficient Values on Smectite and Mixed‐Layer Illite/Smectite Minerals

Sodium‐K, Na‐Ca, Na‐Mg, and Na‐Sr exchange isotherms were performed at a total Cl concentration of about 0.005 mol L−1 on the fine fraction (&lt;2 μm) of MX80 montmorillonite, mixed‐layer illite smectite minerals (IS), and clayey stones from European underground research laboratories. The derived selectivity coefficients for Na‐K, Na‐Ca, Na‐Mg, and Na‐Sr were found to vary very significantly as a function of the exchanger composition. A model was built to reproduce the data, taking into account the change of selectivity coefficient as a function of the exchanger composition of smectite. Model parameters were fitted using data from the present study and data from the literature obtained on smectite minerals. The addition of parameters for cation–anion pairs was found to improve the fitting results. The model was then successfully tested to reproduce published cation‐exchange features on natural clayey materials and soils suspended in fresh or saline water. Finally, it is shown that the simple combination of this smectite exchange model with a previously published illite exchange model is quite successful although perfectible in reproducing exchange data on IS.

Negative Wien Effect Measurements for Exploring Polarization Processes of Cations Interacting with Negatively Charged Soil Particles

The Wien effect, that is, the dependence of the electrical conductivity of dilute suspensions of soil particles on electrical field strength, was explored in the intermediate field‐strengths range of 0.9 × 106 to 5 × 106 V m−1, at higher resolution than in previous studies. This enabled the detection of a local minimum in the electrical conductivity–field strength relationship in which the declining phase is termed the negative Wien effect. Suspensions of clay‐size soil particles of three soil types, with various mono‐, di‐, and trivalent cations, were tested. A negative Wien effect was observed with homoionic soil particles saturated with divalent cations, with electrodialyzed soil particles, and with suspensions of black soil particles that contained organic matter. Two quantifiers of the declining and increasing slopes: (i) polarizability (counter ion polarization and re‐adsorption); (ii) ion‐stripping intensity—on the respective sides of the local minimum were used for characterizing the interaction between the soil particles and the counter ions. The higher mean ion‐stripping intensities found for the Na+ suspensions—twice those for the K+ suspensions—reflect the easier stripping off of the Na cations and the stronger adsorption of the K cations. The mean ion‐stripping intensities of all divalent cations for the three soils were lower than those determined for the monovalent ones, which reflects the tighter binding of the divalent cations. The Ca2+ and Zn2+ ions were stripped off most easily from the surfaces of soil particles, and tighter binding was found for Pb2+ to brown soil and black soil, and for Cd2+ to yellow‐brown soil. In general, lower polarizabilities were correlated with higher ion‐stripping intensities (e.g., for Ca2+ and Zn2+). However, the exceptions (e.g., the polarizabilities of Cu2+ and Pb2+) shed more light on the interaction between the soil particles and the cations. The proposed method of characterization is superior to other methods for characterizing soil particle–counter ion interactions because it characterizes adsorption directly and not via exchange measurement, and it is less laborious than, for example, exchange isotherm measurements.

Isotherm of exchange of sodium and copper cations on ferrimanganese concretions

Isotherm of ion exchange of Cu2+ and Na+ cations on ferrimanganese concretions was studied. The ion exchange is described by an equation similar to that of the Langmuir isotherm. The limiting sorption and apparent ion-exchange constant were calculated.

Cation exchange equilibria of cesium and strontium with K-depleted biotite and muscovite

Cation exchange selectivity for Cs + and Sr 2+ with K-depleted biotite (Na-biotite) and K-depleted muscovite (Na-muscovite) was determined with equilibration for 4 weeks at room temperature. The cation exchange isotherms and Kielland plots indicated that both K-depleted micas show high selectivity for Cs + at low equivalent fraction of Cs + on solid. The K-depleted micas took up Cs up to approximately 50% of their theoretical cation exchange capacities. The XRD patterns after Na + → Cs + exchange reactions with K-depleted biotite showed that the d(001)-spacings collapsed from ~ 12.2 to ~ 11.2 Å with high Cs + concentrations. This collapse suggests that K-depleted biotite is able to immobilize or fix Cs ions in the interlayers. In case of 2Na + → Sr 2+ exchange, K-depleted biotite showed high selectivity for Sr ions at low equivalent fraction of Sr 2+ on solid. The XRD patterns showed that the main d(001)-spacing of the K-depleted biotite slightly increased from 12.16 Å to ~ 12.3 Å after the exchange reactions with the high Sr 2+ concentrations. These results suggest that K-depleted biotite could be used as an ion exchanger to remove radioactive 137Cs as well as 90Sr from groundwater.

Effect of particle size on cesium exchange kinetics by K-depleted phlogopite

Cation exchange mechanism and rate of Cs + exchange were investigated in < 2 μm and 20–2 μm particle size fractions of K-depleted phlogopite (Na-phlogopite). The K-depleted phlogopite was prepared from a natural phlogopite by a potassium removal method using sodium tetraphenylborate (NaTPB) at room temperature. X-ray diffraction (XRD) patterns revealed that interlayer K + ions were completely replaced with sodium ions after the potassium removal treatment. Ion exchange isotherms and kinetics were determined for Na + → Cs + exchange with two particle size fractions. The isotherms indicated that both particle size fractions showed high selectivity for Cs +. Based on the isotherm tests, ΔG o values of < 2 μm and 20–2 μm particle fractions were − 6.83 kJ/mol and − 7.08 kJ/mol, respectively. Kinetics of Cs exchange revealed that the 20–2 μm particle size fraction of the K-depleted phlogopite took up more Cs + ions than the < 2 μm particle size fraction. Various kinetic models were applied to describe Na + → Cs + exchange process. Elovich model described the kinetic data of the < 2 μm particle size fraction well, while the modified first-order model or parabolic diffusion model described the data of the 20–2 μm particle size fraction well.

ISOMORPHOUS SUBSTITUTION OF P(V) IN NATURAL CLINOPTILOLITE: EVALUTION OF THE PRODUCT FOR REMOVAL OF NO3-, NO2- AND F- FROM AQUEOUS SOLUTIONS

Nitrate is an anion of major importance particularly in biological areas. Excessive amounts in water supplies indicate pollution from sewage or agricultural effluents. The effects of excessive quantities of nitrate in water are well known. In this research structural modification of natural clinoptilolite by isomorphic substitution was performed. Isomorphously substituted zeolite was prepared under melting conditions from natural clinoptilolite. It was characterized by XRD, XRF, DTG and SEM techniques. The characterization process revealed that product is different from AlPo. Ion exchange property of the modified product was studied for NO3-, NO2- and F- ion. The uptake of F- was higher than those of NO3- and NO2-. Anion exchange isotherms were constructed for NO3- and discussed. The ion exchange chromatography and neutron activation technique were used to study the extent of the exchange.

The heats of exchange of transition metal ions on the Na form of clinoptilolite

Direct calorimetric measurements were used to determine the heats of exchange of the Mn2+, Co2+, Cu2+, and Ni2+ cations on the Na form of clinoptilolite over the entire range of solid phase fillings with sorbed cations. In parallel, ion exchange isotherms for the systems were measured by the sorption-analytic method. The integral free energies and entropies of ion exchange were calculated. It was shown that the solution phase of the clinoptilolite-electrolyte solution two-phase system contributed significantly to the total thermodynamic characteristics of ion exchange. The differentiation of the dependence of the integral enthalpy on the degree of filling was performed to show that the clinoptilolite structure contained at least two types of exchange sites having different interaction energies with transition metal ions.

Multicomponent ion exchange isotherms in NaX zeolite: evaluation of Cr/Ca/Mg, Cr/Ca/K and Cr/Mg/K systems

AbstractBACKGROUND: One of the most important heavy metals is Cr3+, which is commonly found together with Ca2+, Mg2+ and K+ ions in tannery wastewaters. Such metals can be removed through ion exchange process using zeolite NaX. Unfortunately, with single exchange mechanisms it is impossible to predict muti‐component and competitive interactions. This work is aimed at overcoming this problem. Ion exchange isotherms of Cr3+, Mg2+, Ca2+ and K+ in ternary mixtures (Cr/Mg/Ca, Cr/Ca/K, Cr/Mg/K) using NaX zeolite at 30 °C, 45 °C and 60 °C are studied and reported.RESULTS: Ion exchange is dependent on temperature, and on the nature and interaction of ingoing cations. Sequential ion exchange occurs where one cation is able to displace another already located in the site. Values of the equilibrium constant of all cations investigated are close to each other, which indicates a weak preference for Cr+3. The affinity order is as follows: for Cr/Ca/Mg–NaX isotherms, Cr3+ &gt; Ca2+ &gt; Mg2+ at 30 °C, Ca2+ &gt; Cr3+ &gt; Mg2+ at 45 °C and Ca2+ &gt; Mg2+ &gt; Cr3+ at 60 °C. For Cr/Ca/K–NaX isotherms the sequence is Cr3+ &gt; Ca2+ &gt; K+ for the three temperatures and for Cr/Mg/K–NaX isotherms, Cr3+ &gt; Mg2+ &gt; K+ at 30 and 45 °C and Mg2+ &gt; K+ &gt; Cr3+ at 60 °C.CONCLUSION: It can be concluded that ions with a high charge such as Cr3+ are not always preferentially removed from multi‐component solution. Therefore, exchanges in NaX zeolite are useful when there is no need to have high chromium removal when compared to the competitive cations investigated here. Copyright © 2008 Society of Chemical Industry

Ion exchange equilibrium between ion exchange membrane and electrolyte solutions

The ion exchange equilibrium between an ion exchange membrane and solutions of different electrolytes was studied. The matrix of the ion exchange membrane used consists of a vinyl polychloride network reinforced by a polyester screen; with quaternary and tertiary ammonium as functional groups. The data, provided by manufacturer, were completed by the experimental determinations of humidity percentage and ion exchange capacity. This paper focuses on the study of exchange reaction between an anion exchange membrane and selected binary and ternary electrolyte solutions. Experimental data are reported for the ion exchange equilibrium of the binary system Cl −/NO 3 −, Cl −/SO 4 2−, NO 3 −/SO 4 2− and the ternary system Cl − − NO 3 − − SO 4 2−. The ion exchange isotherms were established and affinity order of ions was given. The prediction of the ternary system based only on the binary data was consistent with the experimental data obtained for this system. Selectivity coefficients K Cl − NO 3 − , K 2Cl − SO 4 2− , K 2NO 3 − SO 4 2− were determined at ionic strength 0.1 M. Ion analyses were performed by ion chromatography, coupled to a conductimetric detector.