The properties of zeolite 4A treated in molten salts
Abstract
The behaviour of zeolite 4A in molten alkali halides, sulphates and nitrates has been investigated. The results achieved show that new zeolite forms are obtained by ion exchange and occlusion. It has also been found out that anion dimensions and temperature affect the extent of occlusion. The heating of LiALiNO3 and NaANaNO3 zeolites at the temperatures above 600°C resulted in new zeolite forms with increased cation exchange capacity, capable only of ion exchange in the melt. Finally, it has been proved that the ion exchange reaction is impossible without a transfer medium in zeolite cavities, which is provided by occluded salt molecules in the melt, and water molecules in aqueous medium.
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Cited by (32)
Two-site equilibrium model for ion exchange between multi-valent cations and zeolite-A in a molten salt
2005, Microporous and Mesoporous MaterialsA model has been developed and tested for its ability to describe the ion exchange of fission product species between zeolite and a molten salt bath used for pyroprocessing of spent nuclear fuel. The model is based on a system at equilibrium and assumes species interacting with zeolite are chemically independent of each other. This assumption was tested via a set of salt–zeolite contact experiments. Zeolite 4A was batch contacted with Cs ternary salt (CsCl–LiCl–KCl), Nd ternary salt (NdCl3–LiCl–KCl) or Cs–Nd quaternary salt (CsCl–NdCl3–LiCl–KCl) until ion exchange steady state was reached. Results from ternary salt and zeolite chemical analyses were used to determine model parameters for all species present. These parameters, in turn, were applied to compute estimated compositions of zeolite contacted with quaternary salt. The estimated compositions compare favorably with results from chemical analyses of the zeolite–quaternary salt experiment samples. Based on the data collected, the model is modified for predictive capability for a range of salt compositions.
Occlusion potential of zeolites for mixed and non-nitrate salts
2003, Microporous and Mesoporous MaterialsOccluded salts in the form of salt complexes exhibit the interesting properties unattainable in bulk state. In this study, occlusion of non-nitrate salts and co-occlusion of mixed nitrate salts were attempted to further expand occlusion potential of zeolites. The non-nitrate salts such as KClO3 and KH2PO4 were occluded by mordenite, although they do not establish stable molten state. Their occlusions were confirmed by 27Al NMR spectra, N2 adsorption/desorption isotherms and thermal analyses. The occluded amounts were relatively less compared to those of nitrate salts. On the other hand, thermal treatment of Na–P1 with a mixture of NH4NO3 and KNO3 resulted in co-occlusion of both NH4NO3 and KNO3 by Na–P1 below the melting temperature of KNO3. The salts in solid state could be introduced into and occluded by zeolites through the interaction with the molten salt present in the salt mixture. The use of salt mixture could lead to co-occlusion of the salts that could be hardly applicable to salt occlusion. Therefore, this study clearly shows that a variety of salts could be applied to salt occlusion by zeolites.
Role of framework on NH<inf>4</inf>NO<inf>3</inf> occlusion in zeolite pores
2001, Microporous and Mesoporous MaterialsSalt occlusion in zeolites is a unique phenomenon and plays an important role in solid and molten state reactions. To elucidate its mechanism, the NH4NO3 occlusion was studied with various zeolites that exhibit diversity in pore shape (channel and cavity), window size, and composition and charge of framework. We also attempted to classify NH4NO3 introduced into zeolite pores by characterizing their properties such as stability against washing with water, thermal behavior, and spectroscopic characteristics. Based on the geometric consideration between zeolite pores and salts, the salts introduced into zeolite pores could be classified as `dispersed', `occluded', and `trapped' salts. This classification was based on their stability against washing with water. Occluded NH4NO3 salts were present in the pores of zeolites such as AlPO4-18, Na-P1 and 4A, while dispersed ones were observed in those of zeolites such as ZSM-5 and 13X. Framework charge was not essential in salt occlusion, although it affected the occluded amount and stability of occluded NH4NO3. It is clear from these results that the requirement for salt occlusion is the proper size fit between the window size of zeolite pore and the size of each ion pair of salt. Occluded salts were stabilized through geometric fit and/or electrostatic interactions with negatively charged frameworks that led to increase in their stabilities against washing with water and thermal treatment. Therefore, the geometric relationship of zeolite pore to salt plays more crucial role in salt occlusion than framework charge.
Zeolite-modified electrodes in electroanalytical chemistry
1999, Analytica Chimica ActaThis review reports on the analytical applications of chemically modified electrodes involving zeolites or zeolite-like materials. After a brief introduction on zeolites, the implication of these solids in electrochemistry is discussed. The interest of zeolite-modified electrodes (ZMEs) for electroanalytical purpose is pointed out, by classifying the applications into five main categories depending on the detection process. In the last decade, successful applications of ZMEs have been achieved. This promising field is thought to lead to significant advances in the near future, because of the explosive growth in the synthesis of novel zeolite-like materials.
The capacity of natural zeolites to occlude ammonium nitrate and potassium nitrate by molten salt treatment has been determined, and the salt-occluded zeolites have been characterized. Molten salt treatment resulted in changes of overall and relative intensities of peaks in X-ray diffractograms of zeolites. The presence of occluded salt in zeolites was confirmed by a i.r. absorption band around 1,390 cm1, exothermic response at 280°C in DTA curve, and type-III nitrogen adsorption/desorption isotherms showing type-H3 hysteresis. The occluded nitrate contents of natural zeolites increased in the following order: erionite > clinoptilolite > chabazite > phillipsite with molten potassium nitrate treatment, and phillipsite > erionite ⩾ chabazite > clinoptilolite with molten ammonium nitrate treatment. The present study shows that the capacity of natural zeolites to store nutrients can be increased by salt occlusion and that these occluded zeolites are potential candidates as slow-release fertilizers.
The study of high-temperature phase transitions in AgA and AgA · AgNO<inf>3</inf> forms. Thermal and X-ray properties
1985, Thermochimica ActaThe study of the thermal behaviour of AgA zeolite and the inclusion complex AgA · AgNO3, within the temperature range from room temperature to 1000°C, has been carried out in this paper. Structural transformations have been investigated and followed by X-ray analysis. The high-temperature transformation of the zeolite A structure of the two silver forms was performed throughout the amorphous phase. The recrystallisation process occurring during any further heating causes formation of the same crystal phase AgAlSiO4, identified as Ag-carnegieite, in both cases. AgA zeolite can be directly transformed into Ag-carnegieite while AgA · AgNO3 passes through a metal inclusion complex intermediate phase, and is then transformed into Ag-carnegieite along with the exolution of a metallic silver phase.