Equilibria and heats of ion exchange in the system of mordenite-alkali and alkaline earth cations

A concurrent absorption analytical study of the ion exchange equilibria and direct microcalorimetric measurement of the heat of ion exchange absorption of K⁺ and Ca²⁺ cations for the sodium forms of two mordenites (NaM) obtained from naturally occurring samples rich in Na⁺ and Ca²⁺ cations has been carried out for the first time. The free energies and entropies of exchange have been calculated. It was shown that the free energy of exchange in the K⁺-NaM system is determined by the enthalpy, whereas in the Ca²⁺-NaM system it is determined by the entropy of solvation. The measured thermodynamic characteristics of exchange were analyzed taking into account the preferred localization of sorption for the cations in the structure. A memory effect in natural mordenites has been established for extra-skeletal K⁺ and Ca²⁺ cations, in the presence of which these zeolites crystallized in nature. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 42, No. 5, pp. 312–317, September–October, 2006.     

Kinetics and Mechanism of the Oxidative Conversion of <Emphasis Type="Italic">n</Emphasis>-Amyl Alcohol to Valeric Acid on a Modified Zeolite Catalyst

The catalytic activity of natural and synthetic mordenites modified with Cu²⁺, Zn²⁺, and Pd²⁺ cations via ion exchange was studied in the oxidative conversion of n-amyl alcohol to valeric acid under the action of oxygen. It is established that the highest activity and selectivity in this reaction is exhibited by mordenite hydrothermally synthesized from kaolinite and containing 3.0 wt % Cu²⁺, 0.1 wt % Pd²⁺, and 2.0 wt % Zn²⁺. The kinetics of this catalytic reaction is studied. Based on the experimental data, a possible stepwise mechanism is proposed, and a theoretically grounded kinetic model of the process is developed.     

Thermodynamics of the Exchange Processes between K+, Ca2+ and Cr3+ in Zeolite NaA

In this paper it was analyzed the ion exchange isotherm of K⁺, Ca²⁺ and also Cr³⁺ ions with NaA zeolites at three temperatures: 30, 45 and 60°C. The NaA isotherms were favorable for the metal cations studied. Differences in shape are due to the different influence of temperature in the interaction of the in-going cation with the zeolite framework. As a consequence, sites of different energies were used in the exchange process, which provided non linear Kielland plots. Equilibrium constant, standard free energy, enthalpy and enthopy changes were measured and tabulated. Equilibrium constant is directly proportional to the in-going ion charge. Concerning enthalpy, endothermic and exothermic exchanges were observed due to differences in the cation-framework interaction. The selectivity order based on the standard free energy over the entire temperature range was K⁺ < Cr³⁺ < Ca²⁺, a consequence of different ion exchange mechanisms. It was also noted that the entropy change increases with the polarizibility of the cations.     

Use of zwitterionic micelles in the eluent II: a new approach to ion chromatographic analysis of inorganic cations in biological fluids with direct sample injection

A new ion chromatographic (IC) technique has been developed for the determination of inorganic cations in biological fluids with direct sample injection. This involved the use of a mixed zwitterionic-micelle/electrolyte solution as an eluent. The proteins in the sample became bound to the zwitterionic micelles in the eluent and were thus eliminated from the column. The cations were separated by cation exchange. This method is ideal for the on-line, simultaneous determination of common inorganic cations (Na⁺, NH₄ ⁺, K⁺, Mg²⁺, and Ca²⁺) in urine and serum samples. Such an application was demonstrated experimentally. Non-suppressed conductivity was used for analyte detection. The detection limits obtained using this IC system were 2.94, 5.22, 34.9, 32.6, and 56.7 μg/L for Na⁺, NH₄ ⁺, K⁺, Mg²⁺, and Ca²⁺, respectively.     

Untersuchungen an Oxidischen Katalysatoren. XXX [1] Charakterisierung der Me2+ -Kationenlokalisierung in CaNaY-, MgNaY- und CaMgNaY-Zeolithen

Studies on Oxide Catalysts. XXX. Characterization of the Me²⁺ Localization in Zeolites CaNaY, MgNaY, and CaMgNaY Data for exchange of the cations Ca²⁺, Mg²⁺, as well as Ca²⁺ and Mg²⁺ into the zeolite NaY have been determined. From this it was concluded on the localization of Me²⁺ cations in hydrated samples. The adsorption of ammonia in the temperature region of 420 to 670 K, the determination of the heats of immersion in water and nitromethane and the Me²⁺ ? CO-interaction indicated by IR spectroscopy yielded informations on the localization of cations in dehydrated samples. The results show that cations Ca²⁺ more selectively than cations Mg²⁺ occupy positions in the small cages. In the case of the competitive cation exchange this fact causes a site directed distribution of cations in zeolite cages.     

Mechanism of simultaneous removal of Ca2+, Ni2+, Pb2+ and Al3+ ions from aqueous solutions using Purolite® S930 ion exchange resin

The sorption mechanism of Ca²⁺, Ni²⁺, Pb²⁺, and Al³⁺on ion exchange resin S930 has been studied as a function of pH in both mono-component and quaternary systems at ion ratio 1:1:1:1. The equilibrium of ion exchange process in mono-component systems has been followed as an adsorption process and it was tested for Langmuir and Freundlich isotherm equations. The selectivity coefficient of the resin for these cations varied in different manners depending on the pH range. The structural characteristics of pores in the initial resin and the resin after contact with synthetic solutions at pH 3.03 and 3.95 have been investigated by using SEM and EDAX techniques.     

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.     

Cation exchange, interlayer spacing, and thermal analysis of Na/Ca-montmorillonite modified with alkaline and alkaline earth metal ions

Na-montmorillonites were exchanged with Li⁺, K⁺, Rb⁺, Cs⁺, Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺, while Ca-montmorillonites were treated with alkaline and alkaline earth ions except for Ra²⁺ and Ca²⁺. Montmorillonites with interlayer cations Li⁺ or Na⁺ have remarkable swelling capacity and keep excellent stability. It is shown that metal ions represent different exchange ability as follows: Cs⁺?>?Rb⁺?>?K⁺?>?Na⁺?>?Li⁺ and Ba²⁺?>?Sr²⁺?>?Ca²⁺?>?Mg²⁺. The cation exchange capacity with single ion exchange capacity illustrates that Mg²⁺ and Ca²⁺ do not only take part in cation exchange but also produce physical adsorption on the montmorillonite. Although interlayer spacing d ₀₀₁ depends on both radius and hydration radius of interlayer cations, the latter one plays a decisive role in changing d ₀₀₁ value. Three stages of temperature intervals of dehydration are observed from the TG/DSC curves: the release of surface water adsorbed (36?C84?°C), the dehydration of interlayer water and the chemical-adsorption water (47?C189?°C) and dehydration of bound water of interlayer metal cation (108?C268?°C). Data show that the quantity and hydration energy of ions adsorbed on montmorillonite influence the water content in montmorillonite. Mg²⁺-modified Na-montmorillonite which absorbs the most quantity of ions with the highest hydration energy has the maximum water content up to 8.84%.     

Infrared-spectroscopic detection and distinction of indium cations of different oxidation states in zeolites

In⁺ cations introduced by reductive solid-state ion exchange into zeolites (Y, ZSM-5, mordenite) and cationic InO⁺ species created by oxidation of the incorporated univalent cations were found to be detectable and distinguishable by IR spectroscopy using pyridine as probe molecule. Relatively weak interactions of In⁺ lattice cations with pyridine give rise, after degassing at temperatures not higher than 370 K, to typical bands at 1446 and 1599 cm⁻¹. After oxidation to InO⁺, these bands are shifted to 1452 and 1610 cm⁻¹, being significantly more resistant towards degassing. Because of restrictions in the accessibility of InO⁺ to pyridine, the respective bands are absent in the spectra of mordenite.     

Preparation of a hybrid monolithic stationary phase with allylsulfonate for the rapid and simultaneous separation of cations in capillary ion chromatography

A hybrid monolithic column with sulfonate functionality was successfully prepared for the simultaneous separation of common inorganic cations in ion‐exchange chromatographic mode through a simple and easy single‐step preparation method. The strong cation‐exchange moieties were provided directly from allylsulfonate, which worked as an organic monomer in the single‐step reaction. Inorganic cations (Li⁺, Na⁺, K⁺, NH₄⁺, Cs⁺, Rb⁺, Mg²⁺, Ca²⁺, and Sr²⁺) were separated satisfactorily by using CuSO₄ as the eluent with indirect UV detection. The allysulfonate hybrid monolith showed a better performance in terms of speed and pressure drop than the capillary packed column. The number of theoretical plates achieved was 19 017 plates/m (in the case of NH₄⁺ as the analyte). The relative standard deviations (n = 6) of both retention time and peak height were less than 1.96% for all the analyte cations. The allysulfonate hybrid monolithic column was successfully applied for the rapid and simultaneous separation of inorganic cations in groundwater and the effluent of onsite domestic wastewater treatment system.     

Radiochemical studies of the sorption behavior of strontium and barium

The sorption behavior of strontium and barium on kaolinite, bentonite and chlorite-illite mixed clay was studied by radioanalytical techniques using the batch method.⁹⁰Sr (29.1 y) and¹³³Ba (10.5 y) were used as radiotracers. Characterization of the solid matrices was done by FTIR and XRD spectrometries and specific surface area measurements. Synthetic groundwater was used as the aqueous phase. The variation of the distribution ratioR _d, as a function of metal ion loading was examined. The sorption isotherms were fitted to various isotherm models. The sorption energies were calculated to be in the range of 8–10 kJ/mol suggesting an ion exchange type of sorption mechanism. In detailed experiments, chlorite-illite mixed clay was first presaturated with K⁺, Sr²⁺, Ca²⁺ and Al³⁺ ions, respectively, prior to sorption studies with Ba²⁺ ions. The results of Ca²⁺ pretreated chlorite-illite were very similar to those of natural chlorite-illite, suggesting that the Ba²⁺ ion exchanges primarily with the Ca²⁺ ion on the clay minerals.     

Investigation of HEU-type zeolite crystals after interaction with Sr2+ cations in aqueous solution using nuclear and surface analytical techniques

Pure HEU-type zeolite (heulandite) crystals were allowed to interact with Sr²⁺ cations in aqueous solution. The powdered solid experimental products obtained from batch-type sorption experiments, using solutions of Sr²⁺-concentrations between 10 and 1000 mg/l, were investigated using INAA, RI-XRF and SEM-EDS. The Sr uptake by the mineral which can adequately be described with a Freundlich-type isotherm, varies from 3.14 to 6.22 mg/g. The distribution coefficients increase progressively by decreasing the solutions concentration reaching a value of 1800 ml/g. The investigated zeolite interacts with Sr²⁺ cations through ion exchange reactions and initial exchangeable Ca²⁺ cations are replaced into the structural micropores. However, in the best case, only ca. 43% of the theoretical CEC can be covered because of the limited availability of the extra framework Ca²⁺ cations that can be removed from the lattice under ambient treatment conditions. The XPS investigation of Sr-loaded single crystals indicated that adsorption of Sr²⁺ cations on the outer surface also occurs while surface precipitation phenomena must be excluded. Similar surface analyses by means of¹²C-RBS showed that the Sr depth-distribution at near-surface layers is quite homogenous in contrast to a previous relevant study revealing an intense surface Sr-accumulation on a natural Ca-zeolite of different structural characteristics (scolecite).     

Heats of adsorption of water on vermiculite having large singly-charged cations in the exchange complex

The isotherms and differential heats of adsorption of water vapor on K-, NH₄-, Rb-, and Cs-vermiculites have been studied by means of a Calvet microcalorimeter having a microweighing adsorption attachment. The results are interpreted taking into account that the large cations K₊, NH₄ ⁺, Rb⁺, and especially Cs⁺, may not replace the initial exchange complexes (Na⁺ or Mg²⁺) of the mineral completely, so that besides hydration of the principal exchange cations the reaction of water molecules being adsorbed with the residual Na⁺ or Mg⁺ cations also takes place. The presence of a certain number of the initial cations (Na⁺ or Mg²⁺) in the Cs form of vermiculite is confirmed by the results of studying the ion exchange equilibria on the Na and natural (Mg) forms of the mineral involving the participation of the Cs₊ ions. The nature of the variation in the dependence of the differential heats of adsorption with an increase in the amount of adsorbed substance indicates the segregation (isolation) of the principal (K⁺, NH₄ ⁺, Rb⁺, Cs⁺) and the residual (Na⁺, Mg²⁺) exchange cation in the structure of the mineral.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 1, pp. 91–96, January–February, 1986.     

Chromium uptake from tricomponent solution in zeolite fixed bed

Removal of Cr³⁺,Ca²⁺,Mg²⁺ and K⁺ in equilibrium isotherms and in tricomponent solutions (Cr/Ca/K, Cr/Ca/Mg and Cr/Mg/K) were investigated in NaX and NaY packed beds at 30^∘C. The equilibrium selectivity was obtained as Cr⁺³ > Mg²⁺ > Ca²⁺≈K⁺ for zeolite NaY and Ca^{2 +}≫Cr^{3 +} > Mg^{2 +}≈K⁺ for zeolite NaX. The breakthrough curves showed sequential ion exchange where chromium ions are able to replace the competing cations. Some mass transfer parameters, such as length of unused bed and overall mass transfer coefficient, were investigated. Chromium retention was also investigated through a mass balance. Based on the breakthrough results, it was concluded that chromium-uptake mechanism was hardly influenced by the competition and interaction between the entering ions. NaY showed a higher affinity towards Cr³⁺ for both equilibrium and dynamic systems and its sites were more efficiently used in the ion exchange process. Chromium was less retained in NaX due to the high selectivity towards calcium ions.     

High-resolution 27Al NMR study of the states of aluminum atoms in modified natural mordenite

High-resolution ²⁷Al NMR has been applied to the states of aluminum in modified natural mordenite. Acid treatment of the natural mordenite and heat treatment of the ammonium form alter the coordination state of 6–8% of the aluminum atoms from tetrahedral (in the framework) to octahecral (at the inner surfaces of the zeolite cavities). In that state, the aluminum can exchange with Na⁺, NH₄ ⁺, and other cations. This change in coordination state should have a considerable effect on the catalytic parameters of zeolites.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, No. 2, pp. 241–244, March–April, 1987.     

A model for cation adsorption to clays and membranes

A cation adsorption model is presented and its recent applications are discussed. The model combines electrostatic equations with specific binding, and considers neutral and positively charged complexes between the negative surface sites and organic cations in a closed system. Extensions in the model account for dye aggregation in solution, and for the formation of solution complexes of inorganic cations, such as [M⁺⁺ Cl^–]⁺. The amounts of 45Ca²⁺ adsorbed to vesicles extracted from the plasma membranes of melon root cells could be adequately simulated and predicted. The binding coefficients determined for Ca²⁺, Na⁺, and Mg²⁺ are in the range of values previously deduced for binding to phospholipid components. Model calculations were applied to the test of hypotheses on the effect of salt stress on the growth of roots. The adsorption of monovalent organic cations to montmorillonite is characterized by binding coefficients that are at least six orders of magnitude larger than those of Na⁺, Mg²⁺, Ca²⁺, and Cd²⁺, or those of CdCl⁺ or CaCl⁺. Monovalent organic cations were found to adsorb 140–200% of the cation exchange capacity of the clay and to cause charge reversal. Deductions from adsorption results of acriflavin are consistent with those drawn from the application of other experimental methods. Preliminary results on the adsorption of divalent organic cations are presented. Agro-environmental applications of organo-clays are discussed.     

Imidazo-benzo-15-crown-5 ethers bearing arylthienyl and bithienyl moieties as novel fluorescent chemosensors for Pd and Cu

Novel fluorescent ionophores bearing imidazo-arylthienyl or imidazo-bithienyl π-conjugated bridges functionalized with one or two fused benzo-15-crown-5 ethers as receptor units are reported. The sensing ability of the compounds in the presence of metallic cations (Li⁺, Na⁺, K⁺, Ca²⁺, Zn²⁺, Cu²⁺, Ni²⁺, Pd²⁺, and Hg²⁺) and fluoride ion was studied in MeCN/DMSO solutions by absorption and emission spectroscopy. The experimental results indicate that all compounds could act as selective fluorimetric sensors for Cu²⁺ and Pd²⁺ and also for the fluoride ion, in the case of the bis-substituted crown ether derivatives.     

Use of Ionic liquids as additives in ion exchange chromatography for the analysis of cations

The behavior of acids (citric acid, nitric acid, oxalic acid, tartaric acid) as a mobile phase and imidazolium ionic liquids (the bromides, tetrafluoroborates and hexafluorophosphates of 1‐ethyl, 1‐butyl, and 1‐hexyl‐3‐methylimidazolium) as additives in ion exchange chromatography for cations (Na⁺, K⁺, Mg²⁺, Ca²⁺) separation were studied. The results showed that nitric acid and 1‐hexyl‐3‐methyl‐imidazolium hexafluorophosphate offered the most interesting features in the separation of cations, such as lower retention time and better resolution. The selected optimal conditions were achieved by adding 0.10 mM 1‐hexyl‐3‐methyl‐imidazolium hexafluorophosphate in 4.0 mM HNO₃ mobile phase for the separation of four cations with the flow rate of 0.9 mL/min at room temperature (25°C). The linear regression equations of Na⁺, K⁺, Mg²⁺, Ca²⁺ were S  = 4.4763c  + 0.0209, S  = 3.8903c  – 0.0087, S  = 6.3974c  – 0.0173, and S  = 7.601c  – 0.0339 and the limits of detection of Na⁺, K⁺, Mg²⁺, Ca²⁺ were 0.296, 4.98, 0.0970, and 1.22 μg/L, respectively. In this work, four cations in samples were successfully detected.     

Indirect ultraviolet detection of alkaline earth metal ions using an imidazolium ionic liquid as an ultraviolet absorption reagent in ion chromatography

A convenient and versatile method was developed for the separation and detection of alkaline earth metal ions by ion chromatography with indirect UV detection. The chromatographic separation of Mg²⁺, Ca²⁺, and Sr²⁺ was performed on a carboxylic acid base cation exchange column using imidazolium ionic liquid/acid as the mobile phase, in which the imidazolium ionic liquid acted as an UV‐absorption reagent. The effects of imidazolium ionic liquids, detection wavelength, acids in the mobile phase, and column temperature on the retention of Mg²⁺, Ca²⁺, and Sr²⁺ were investigated. The main factors influencing the separation and detection were the background UV absorption reagent and the concentration of hydrogen ion in ion chromatography with indirect UV detection. The successful separation and detection of Mg²⁺, Ca²⁺, and Sr²⁺ within 14 min were achieved using the selected chromatographic conditions, and the detection limits (S /N = 3) were 0.06, 0.12, and 0.23 mg/L, respectively. A new separation and detection method of alkaline earth metal ions by ion chromatography with indirect UV detection was developed, and the application range of ionic liquids was expanded.     

Quantum-chemical investigation of the localization and hydration of Ca<Superscript>2+</Superscript> and Mg<Superscript>2+</Superscript> cations in eight- and ten-fold structural rings in the clinoptilolite structure

The hydration of Ca²⁺ and Mg²⁺ exchange cations in solution and in 10- and 8-membered silicon—oxygen rings of the clinoptilolite was studied by ab initio and MNDO quantum-chemical methods. The coordination numbers of these cations with respect to water molecules and their hydration energies were determined. It is shown that the localization of Ca²⁺ and Mg²⁺ in the clinoptilolite structure was different for the dehydrated state and the partially hydrated state. The ion exchange sorption energy calculated for the Ca²⁺—Mg-Cli system was in satisfactory agreement with the experimental data.Translated from Teoreticheskaya i Éksperimentalnaya Khimiya, Vol. 40, No. 6, pp. 357–362, November–December, 2004.