Standard Free Energy Of Exchange Research Articles

Long-term differences in nutrient management under intensive cultivation alter potassium supplying ability of soils

Despite removal of potassium (K) by crops in large quantities, often exceeding that of nitrogen (N), K fertilization has long been neglected compared with N and phosphorus (P) in Indian agriculture leading to mining of soil K. We, therefore, studied the effect of long-term fertilization (with or without K) on K supplying ability of two major soil orders of India, viz. Inceptisol and Vertisol after more than four decades of cultivation. Soil samples (0–15 and 15–30 cm) were collected after the completion of 43 (Inceptisol) or 42 (Vertisol) cropping cycles from on-going long-term experiments located at New Delhi (Inceptisol) and Jabalpur (Vertisol), India, from six treatments, viz. no-fertilization (control), recommended N (N), N and P (NP), N, P and K (NPK), 150% NPK and NPK + farmyard manure (NPK + FYM), along with adjacent uncultivated land. Ammonium acetate extractable K (Kex), non-exchangeable K (NEK), quantity-intensity relationship and K release kinetics along with grain yields and K uptake by crops were studied. The Kex and K-saturation of exchange complex in both soils and NEK in the Inceptisol were the lowest under NP followed by N. Cropping without K input resulted in lower quantity (non-specifically and specifically held K i.e. –ΔK0 and Ks) and intensity (equilibrium activity ratio i.e. AReK) of K in both soils. More negative values of standard free energy of exchange (ΔG0) under cultivation without K in both soils indicated increased affinity of soil solids for K+ owing to K omission. The gap between equilibrium exchangeable K (EK0) and minimum exchangeable K (EKmin) was significantly lower under cropping without K than with K in the Vertisol. Imbalanced fertilization (N or NP) also showed noticeably smaller cumulative K releases and slower rates of replenishment of solution K by solid phase K in both soils. Interestingly, even under cropping with K fertilization at either experimental site, several K supply parameters showed decline compared with adjacent uncultivated soil. Grain yields of wheat and total K uptake by all crops (maize and wheat in Inceptisol; soybean and wheat in Vertisol) showed significant and positive response to K application. The study showed variable effect of long-term intensive cropping with or without K input on the K supplying ability of an Inceptisol and a Vertisol. The findings underlined inadequacy of the existing K fertilizer recommendations, and the need for their refinement to minimize native K mining and sustain K supplying ability of soils.

Thermodynamic and kinetic studies on Cs+- and Sr2+-exchange in natural zeolite from Akita, Japan

Thermodynamic and kinetic studies on the adsorption of Cs+ and Sr2+ by Na-exchanged clinoptilolite-rich zeolite rock from Akita (Northern Japan) were performed for the purpose of nuclear waste treatment. The thermodynamic parameters such as selectivity coefficient, thermodynamic equilibrium constant, and standard free energy of exchange were evaluated. These values indicated that the selectivity order was determined as Cs+ > Na+ > Sr2+. In order to discuss the adsorption mechanism of Cs+ and Sr2+ onto Na-exchanged clinoptilolite, the effective diffusion coefficients were calculated and two kinetic models, pseudo-first-order and pseudo-second-order kinetic model, were tested. For all systems studied, chemisorption seems significant in the rate-controlling step, and the pseudo-second-order kinetic model provided the best correlation of the experimental data.

Ion exchange properties of natural clinoptilolite: lead–sodium and cadmium–sodium equilibria

Abstract In the present work, ion exchange of lead and cadmium on the sodium form of Western Anatolia clinoptilolite is examined at 25 °C and 0.1 total normality. Its total theoretical cation exchange capacity was 2.3 meq/g. But only the sodium was exchanged during the equilibrium experiments. On this basis, the theoretical exchange capacity is 1.74 meq/g. According to the equilibrium studies, the selectivity sequence can be given as Pb 2+ >Na + >Cd 2+ . The maximum exchange levels expressed as the percentage of the theoretical exchange capacity were 100% for lead and 54% for cadmium. Using the equilibrium data, the thermodynamic analysis of the system was carried out. The solution non-ideality correction factor has almost no effect on the Kielland plot and so on the numerical values of the thermodynamic equilibrium constant. The thermodynamic equilibrium constant ( K a ) and the standard free energy of exchange (Δ G °) were calculated as 16.6 and −3.48 kJ/eq. for lead–sodium system; and 0.16 and +2.27 kJ/eq. for cadmium–sodium system, respectively. Comparing the results of the present work with the data in literature, it can be concluded that the ion exchange capacities and cation selectivities of clinoptilolites with different cationic compositions are different. So, one should carry out cation exchange experiments on representative samples from the deposit before using it as cation exchanger for any practical application.

Thermodynamics of Potassium–Magnesium Exchange in Two Alfisols of Northern Greece

The exchange behavior of potassium (K) in soils has been extensively studied relative to a dominant cation, which in most cases was considered to be calcium (Ca). Magnesium (Mg) was tacitly assumed that existed in minor quantities or that it had the same exchange behavior with Ca. However, under certain conditions and practices (Mg-rich soils, greenhouse crops) Mg can become an important component of the soil exchange complex participating drastically in the exchange reactions. Consequently, the exchange behavior of the pair K–Mg has merit and in this study the thermodynamics of exchange for this pair were evaluated in two Alfisols with different mineralogical composition of the clay fraction. The exchange reaction was studied in both directions, namely, Mgsoil→Ksoil and Ksoil→Mgsoil. Comparison of the experimental exchange isotherms to the non-preference isotherms revealed that both soils exhibited preference for K relative to Mg. Standard free energies of exchange (ΔG0) for the reaction Mgsoil→Ksoil were negative (−5.7 to −6.7 kJ mol−1) indicating the spontaneity of the reaction and that the formation of a K-soil is favored. Also, ΔG0 values for the reaction Ksoil→Mgsoil were positive (7.3 to 7.5 kJ mol−1) which indicated the reluctance of K-soil to be converted to Mg-soil, thus corroborating the previous findings. Standard enthalpies of exchange (ΔH0) were negative (−8.7 to −13.5 kJ mol−1) for the reaction Mgsoil→Ksoil and positive (13.8 to 15.1 kJ mol−1) for the backward reaction suggesting a strong binding of K with some sites of the soils. Vanselow selectivity coefficients (KV) showed a stronger preference for K in the soil where mica-type minerals dominated the clay fraction. Selectivity for K, as judged by the KV values, was also strongly K-saturation dependent; the lower the degree of K saturation the higher the selectivity for K. Under the conditions of the experiment the exchange reaction of the pair K–Mg was not reversible but exhibited hysteresis, the magnitude of which was more pronounced in the soil where mica-type minerals were prevalent in the clay fraction.

The Selective Binding of Carboxylate Ions at Cationic Surfactant Solution/Air Interfaces

In this study the binding of a homologous series of single chainn-alkyl carboxylates (formate through octanoate) to the tetradecyltrimethylammonium surfactant cation has been investigated using ion flotation. The binding of these ions to the interface is mainly due to their hydrophobicity. In this series, methylenes are added sequentially and the effect of the increase in the number of methylene groups on binding is determined. The selective binding of one carboxylate over the other is quantified in terms of a selectivity coefficient and the standard free energy of exchange. The results show that there is complete transfer of the hydrophobic tail from the aqueous phase to the interface in the case of the longer chain carboxylates, beginning with pentanoate, but that shorter chained compounds are largely electrostatically bound.

ChemInform Abstract: EXCHANGE OF AMMONIUM AND SODIUM IONS IN SYNTHETIC FAUJASITES

AbstractIonenaustausch‐ Isothermen für das Na F′ NH4‐G1eichgewicht in Zeolithen Xund Ywurden bei 298 K und einer totalen Lösungsnormalität von 0.1 g‐Äquiv.

Exchange of ammonium and sodium ions in synthetic faujasites

Ion-exchange isotherms for the Na ⇌ NH4 equilibrium in zeolites X and Y were constructed at 298 K and a total solution normality of 0.1 g-equiv. dm–3. Values for the standard free energy of exchange were calculated and shown to be consistent with the affinity sequence predicted using dielectric theory. Comparisons are made between previously reported studies on the Na ⇌ NH4 exchange in X and Y and this current work, and the differences in experimental data are discussed. Statistical thermodynamic considerations provide a greater understanding of the Na ⇌ NH4 exchange equilibrium in X and Y, and collectively the evidence suggests that high framework charge and ion-sieving factors in X are the dominant properties determining exchange selectivity and maximum exchange levels in this zeolite. In Y, the ion-sieve effect and repulsion between the entering ammonium ions are the dominant factors.

Exchange of alkylammonium ions in the zeolite-L

A study has been made of the ion-exchange equilibria of NH+4, CH3NH+3, C2H5NH+3, n-C3H7NH+3, n-C4H9NH+3, (CH3)2NH+2, (CH3)3NH+, (C2H5)2NH+2 and (C2H5)3NH+ by the zeolite L. None of the alkylammonium ions could effect a complete replacement of the cations initially present in the zeolite. The maximum extent of exchange and the standard free energy of exchange were related to the molecular weight of the entering alkylammonium ions.It is suggested that there was an equilibrium distribution of the exchangeable cations over the different sites (C and D), governed by the nature and affinity of the entering alkylammonium ion and the cation initially present in the zeolite.

Thermochemical aspects of anion exchange reactions—I: Exchange reactions involving Cl −, OH − and H 2PO 4− ions

Thermodynamic equilibrium constants for the H 2 PO 4 − Cl − and OH − Cl − exchange reactions on Dowex 1 × 8 at 25°C have been determined at 0.1 total normality. The standard free energy of exchange was combined with the standard enthalpy of the exchange obtained from calorimetric measurements to obtain the standard entropy of the exchange. The Cl −-form resin shows little affinity for the OH − and H 2PO 4 − ions because in each case there is an unfavourable (i.e. endothermic) enthalpy change. Although there are favourable (i.e. positive) entropy change for the exchanges, ΔG° is in both cases positive because of the dominant enthalpy term.

Transition metal ion exchange in zeolites. Part 2.—Ammines of Co3+, Cu2+ and Zn2+ in clinoptilolite, mordenite and phillipsite

Exchange of cuprammine and zincammine ions in ammonium forms of clinoptilolite, mordenite and phillipsite has been studied in ammoniacal solution, pH > 10, and similar investigations are reported on the [Co(NH3)6]3+ ion at pH values of ∼5 and ∼10 in mordenite. Isotherms were too rectangular to calculate values of the standard free energy of exchange, and selectivities were very much higher than for the corresponding aquo ions in mordenite at low pH. Analyses of the zeolites revealed that the intracrystalline Cu2+ and Zn2+ ions had ∼three NH3 ligands and that the cobaltic ion retained six NH3 molecules. The increase in selectivities observed with mordenite when the cobalt, copper and zinc ions were complexed with ammonia has been rationalised in terms of dielectric theory.

Ion exchange in mordenite

Ion-exchange isotherms have been measured for synthetic mordenite involving the cation pairs Na+⇌Cs+, NH+4⇌K+, NH+4⇌Na+, NH+4⇌Li+, 2NH+4⇌Ca2+, 2NH+4⇌Sr2+ and 2NH+4⇌Ba2+. In all cases except those involving Ca2+ and Sr2+ reversible exchange was effected. The values of the thermodynamic equilibrium constant, Ka, and the standard free energy of exchange, ΔG⊖, were calculated for the reversible pairs. For additional combinations of the reversible ionic pairs, Ka and ΔG⊖ were obtained using the triangle rule. The thermodynamic affinity sequence is Cs+ > K+ > NH+4 > Na+ > Ba2+ > Li+. The thermodynamic affinity sequence among monovalent alkali metal ions established in this work for mordenite was found to be repeated for other zeolites, provided exchanges which do not go to completion are normalised by considering the equilibrium only in terms of the exchangeable fraction of the ions.

Accumulative Effects of Manure and N on Continuous Corn and Clay Soil. II. Chemical Changes in Soil1

AbstractContinuous corn (Zea mays L.) was grown on a Panton clay soil (Typic Ochraqualf). Four rates of manure (0, 22, 44, and 66 tons/ha) and five rates of N (0, 56, 112, 168, and 224 kg/ha) were combined in a factorial arrangement and applied each year to the same plots. Also, 120 kg/ha of P and 90 kg/ha of K were applied for 4 years to all plots. Maintenance of structure and fertility had been difficult in this soil. It had not been intensively cultivated even though it lay in large, level fields.The objectives were to study the effects of the treatments on growth, yield, and nutrient uptake of corn and on the physical and chemical properties of the soil over a period of 5 years (six crops). Results of the first objective have been previously published (7) and effects chemical properties will be reported here.Cultivation and cropping for 5 years on the check plots reduced organic matter; (by N) 8.7% and OM (by 17.7%. An annual application of 44 tons/ha of fresh dairy cattle manure was needed to maintain soil OM. CEC was increased by manure treatments as would be expected from increase in soil OM.Soil test results (pH 4.8, NH4OAc extractions) showed that P from manure was more available than fertilizer P; 119 kg/ha of P from manure increased soil test P about the same as 480 kg/ha of P from fertilizer. However, K, either from manure or fertilizer, was readily fixed by the soil (60 to 75% of the applied). More than 414 kg/ha of K was needed to bring K potential in soil to the −3,500 calorie level suggested as adequate for standard free energy of exchange of K for Ca and Mg (13).Manure application up to 44 tons/ha did not contain enough Ca or Mg to maintain initial levels in the soil. Manure and N treatments had no measurable effects on Fe and Na levels in the soil. Averaged over all treatments, exchangeable Na decreased from 123 to 85 kg/ha and Mn from 45 to 20 kg/ha during the 5 years (1966 to 1971). Treatments of N did not affect rate of breakdown of OM nor decrease pH. The highest rate of N, compared to check plots, slightly increased Mn extracted (by 6 kg/ha). The highest rate of manure decreased extractable Mn (8 kg/ha) and AI (5 kg/ha).These data showed the value of fresh manure as a soil amendment in addition to its nutrient content. Land applications of manure should be encouraged as a method of disposal but its agronomic value emphasized to encourage use with a minimum of loss.

Calcium-Magnesium Exchange in Montmorillonite and Vermiculite

AbstractAn experimentally determined Ca-Mg exchange isotherm of montmorillonite is reported. The selectivity coefficient of this exchange over a wide range of Mg saturation was calculated and found constant.Standard free energies of exchange, thermodynamic equilibrium constants and activity coefficients of the exchangeable Ca and Mg ions in vermiculite and montmorillonite, were predicted from knowledge of the microstructure of these two clays, assuming that coulombic forces are the main ones playing a role in the interaction between the counterions and the charged clay surface. The standard free energies of exchange (ΔGCa°Mg = 238 cal/mole) predicted a preference for Ca in montmorillonite and a preference for Mg in vermiculite (ΔGCa°Mg = - 1665 cal/mole). The predicted thermodynamic equilibrium constants were compatible with the experimentally determined selectivity coefficients KsCaMg = 0·67 as compared with KsCaMg = 0·68 in montmorillonite, which remains constant over all the range of Mg saturation, and KCaMg = 16·7 as compared with KsCaMg = 13·9 in vermiculite at 95% Mg saturation. The activity coefficients of Ca and Mg counterions in montmorillonite were found to be and , respectively, and to remain constant. The activity coefficients of exchangeable Ca and Mg in vermiculite were found to be and , respectively, at an equivalent fraction of unity. The activity coefficient of exchangeable Mg increased as the saturation with Mg decreased, and was found to be 1·7 × 10-3 in the range of the low Mg saturation.The microstructure, the isomorphic substitution and the surface charge density provided an understanding of the changes taking place in the activity coefficients of the counterions.

Influence of framework charge density on ion-exchange properties of zeolites

Ion-exchange isotherms have been measured at 25°C for the high framework charge chabazite-type zeolite, K-G1, and involving the cation pairs: K+⇌ Na+, Na+⇌ Li+, Na+⇌ Cs+, Na+⇌ Ca2+, Na+⇌ Sr2+, and Na+⇌ Ba2+. The results have been compared with those for an isostructural natural chabazite of lower charge density. The values of the thermodynamic equilibrium constants show that the larger ion is preferred by the zeolite of lower charge density. In terms of a solid state reaction involving exchange of ions between both zeolites, the standard free energy of exchange is negative if the larger ion goes from G1 to chabazite. All these results can be explained in terms of dielectric theory if the local dielectric constant in solution is greater than that in either zeolite, and if this constant is greater in a given cationic form of the zeolite of high charge density than in the corresponding form of the zeolite of lower charge density. The correctness of these assumptions for the zeolites was supported by measurements of the refractive indices. The exchanges involving caesium are incomplete in both G1 and the natural chabazite. The different limiting values for these two exchangers have been discussed in terms of steric, electrostatic and hydration effects. The pattern of exchange behaviour observed is consistent with that reported previously for the isostructural zeolites X and Y.

Ion exchange equilibria in synthetic zeolite 4 A in a mixed solvent system

The ion exchange behaviour of alkali metal ions on synthetic zeolite 4 A in the water-methanol system has been studied as a function of D, the macroscopic dielectric constant of the external solution. The anomalous behaviour of Li + in the presence of organic solvent is observed. Applying a statistical-thermodynamic treatment, thermodynamic equilibrium constants are determined; from these the standard free energies of exchange are evaluated for the systems Na + ↔ M + ( M + = Li +, K +, Rb +and Cs +) in a 50 mole % water-methanol mixture. The thermodynamic affinity sequence, based on the standard free energies of exchange, is Na + > K + > Rb + > Cs + > Li +.

Standard Heats and Entropies of Exchange for Alkali Metal Cations on Wyoming Bentonite

AbstractStandard heats of exchange, ΔH°, were determined for alkali metal cation exchange on Wyoming bentonite using a Calvet microcalorimeter. In addition, values of ΔH° for Na‐Cs, Na‐Rb, and Cs‐Rb exchange were evaluated from selectivity measurements conducted at 25 and 50C. Standard entropies of exchange, ΔS°, were calculated by combining the standard heats with free energy values, ΔG°, estimated from equilibrium selectivity coefficient determinations using the relationship ΔG° = ΔH° − TΔS°. Values of ΔH° varied from +150 cal mole‐1 for Na→Li exchange to −2,557 cal mole‐1 for Na→Cs exchange. Values of ΔG° ranged from +48 to −1,081 cal mole‐1 for these reactions giving values of ΔS° ranging from +0.5 to −4.9 cal mole‐1 deg.‐1. Both ΔH° and ΔS° were always negative for uptake of the preferred cation with the absolute values increasing with the degree of selectivity. While the entropy changes did contribute significantly to the standard free energies of exchange, they were only about 10% of the hydration entropy differences for Na‐Li and Na‐K exchange and 26 and 41% for Na‐Rb and Na‐Cs exchange, respectively.

Standard Free Energies of Exchange for Alkali Metal Cations on Wyoming Bentonite

AbstractStandard free energies of exchange, Δ Go, were determined for the exchange of Na with Li, K, Rb, and Cs and Li with K between 0.001N chloride solutions and 5% Wyoming bentonite gels at 25C. Values were also determined for Na → Rb, Na → Cs, and Rb → Cs exchanges between 0.0075N chloride solutions and 0.75% Wyoming bentonite suspensions. Application of the additivity rule indicates that the values are accurate to within ±50 to 100 cal mole‐1. Values for the 5% gels range from +48 cal mole‐1 for Na → Li exchange to −1,081 cal mole‐1 for Na → Cs exchange. There is a small but consistent increase in the ΔGo values for the 0.75% suspensions compared to those for the 5% gels. With the possible exception of Li, a linear relationship was found between ΔGo values and Debye‐Huckle parameters for the respective cations indicating that the adsorption of monovalent cations from strong electrolyte solutions is governed by their hydrated radii.

Thermodynamics and thermochemistry of cation exchange in chabazite

A quantitative study has been made of the exchange of Li +, K +, Rb +, Cs +, Ag +, Tl +, NH 4 +, Ca 2+, Sr 2+, Ba 2+ and Pb 2+ with Na + in a natural chabazite. All the ions except Cs + exchanged almost completely with Na +. From the isotherm contours, Kielland plots and differential heat curves attempts have been made to determine cation positions in the zeolite. For the ions that exchange almost completely the thermodynamic affinity sequence, based on the standard free energies of exchange, is Tl + > K + > Ag + > Rb + > NH 4 + > Pb 2+ > Na + = Ba 2+ > Sr 2+ > Ca 2+ > Li +. Heats of exchange were determined calorimetrically and were negative when K +, Rb +, Cs +, Ag +, Tl + and NH 4 + in the zeolite, and positive when Na + was replaced by Li +, Ba 2+ and Pb 2+. Exchanges involving Ca 2+ and Sr 2+ were so slow that it was not possible to determine equilibrium heats of exchange.

Ion exchange in synthetic zeolites. Part 1.—Ammonium and some of its alkyl derivatives in Linde Sieves X and Y

A study has been made of the exchange adsorption of NH+4, CH3NH+3, C2H5NH+3, iso-C3H7NH+3, n-C4H9NH+3, (CH3)2NH+2, (C2H5)2NH+2, (CH3)3NH+ and (C2H5)3NH+ by Linde Sieves X and Y. For steric reasons, none of these ions could effect a complete replacement of the Na+ ions initially present in the zeolite so that the exchange reaction was confined to the large cavities in the crystal. The maximum extent of exchange decreased with an increase in molecular weight and polarizability of the cations but was always below the limit imposed by the space requirement of the respective ions. This decrease was also greater for the di- and trialkyl derivatives than for the monoalkylammonium ions of comparable molecular weight and was more pronounced in X than in Y. A similar relationship was obtained between the standard free energy of exchange and molecular weight. These observations have been interpreted in terms of the increased difficulty of packing the larger and more branched species in the spherical large cavities of the crystal and of the affinity of the organic ion for the zeolite. The importance of affinity of the cations in determining the upper limit to exchange was further shown by the observation that for a given alkylammonium ion this limit decreased with an increase in the affinity of the inorganic ion which it replaced from the zeolite, the order being Li > Na > K > Ag > Tl(I). It is suggested that there was an equilibrium distribution of the exchangeable ions over the different crystallographic sites, this distribution being governed by the nature of the entering alkyl-ammonium ion and of the cation initially present. If the affinity of the organic ion for the zeolite is relatively great, varying proportions of the inorganic ions may vacate their places inside the network of small cavities and enter the large cavities. For the larger alkylammonium ions having a low affinity for the zeolite or when the ions to be replaced were strongly bond to the zeolite framework (Ag+ and Tl+), the limit to exchange may fall below that corresponding to the minimum population of exchangeable ions inside the large cavities. A correlation was also found between the upper limit to exchange and the ionic potential (for inorganic ions) and the dipole moment of the corresponding alkylamine indicating that electrostatic attraction was of greater importance than van der Waals forces in determining exchange.

Thermochemistry and thermodynamics of ion exchange in a near-faujasite

The thermochemistry and thermodynamics of the exchange of Li +, K +, Rb +, Cs +, Ca 2+, Sr 2+ and Ba 2+ with the Na + ions in Linde Sieve X have been investigated. At 25°C complete replacement of Na + by Rb +, Cs + and Ba 2+ could not be achieved; 35 per cent of the Na + was not exchanged by the monovalent ions and 26 per cent of the Na + was not replaced by Ba 2+. These limits to the exchange are helpful in elucidating the cation site positions in the zeolite. From the determination of the standard free energy of exchange, ΔG°, the following affinity sequence was established: Li + < Na + < Ca 2+, K + < Sr 2+, Cs + < Ba 2+ < Rb +. In this affinity series ΔG° is derived from the value of the equilibrium constant formulated with maximum obtainable exchanges taken as 100 per cent exchange. The standard heats of ion exchange ΔH° were found to be negative whenever a larger monovalent ion replaced a smaller one and also when Ba 2+ replaced Na + but when Ca 2+ and Sr 2+ replaced the reaction was endothermic. In the exchanges involving the divalent ions, equilibrium was not attained in the calorimeter and ΔS° for these exchanges could not be derived. With the monovalent ions, however, ΔS° was found to be negative when a larger monovalent ion replaced a smaller one.