Salt Occlusion Research Articles

Innovative Inorganic Synthesis

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Study on the Characteristics of the Ion Exchange of Zeolite 4A in a Molten LiCl System

An advanced spent fuel management process using a molten LiCl salt for the purpose of reducing spent oxide fuel to a metallic form generates a waste salt containing alkali, alkaline-earth, and some rare-earth fission products. A periodic removal of the high heat-generating Cs and Sr should be accomplished to reuse the salt since a recycling of the LiCl waste salt to a process stream is required to decrease the total amount of waste to be disposed of. In this study, zeolite 4A was proven to have desirable properties for the removal of the Cs and Sr elements from an LiCl molten salt phase, and the ion-exchange characteristics of zeolite in the molten salt were investigated. The adsorption of the Cs and Sr elements in an LiCl molten salt reaches nearly a constant value after 2–4 h of contact with the zeolite. The salt-occluded zeolite was produced in an LiCl molten salt, and then its ionexchange and salt occlusion properties were studied experimentally. The result indicates that zeolite 4A occluded between 10 and 11.5 salt molecules, and the salt-occluded zeolite was found to be a very effective molecular sieve for sorbing the Cs and Sr in the LiCl waste salt.

기능성 Zeolite-KCIO3복합체에 의한 Chlorothalonil의 분해

Salt occlusion in Zeolite is a unique phenomenon that takes place only when the salt size is similar to the window size of host zeolite. -occluded Zeolite, as an environment-friendly oxidant, has a high potential for effective removal of various organic pollutants. This study was carried to investigate the characteristics and the removal kinetics of fungicide chlorothalonil by zeolite- complex. About 10% of was occluded in zeolite pores synthesized by salt-thermal method from fly ash, although the occlusion amount was relatively less compared to that of nitrate salts. By occlusion with , no remarkable changes were found in X-ray diffraction patterns of cancrinite, whereas some decrease of overall peak intensities was found with those of sodalite. Different releasing kinetics of ion were observed in distilled water and soil solution from zeolite- complex. Two reactions, hydration and diffusion, seem to be related with the release of . Therefore, the release isotherm of ion well fitted to the power function model which indicate the release was made by hydration and diffusion. The removal of chlorothalonil by zeolite and reached at reaction equilibrium within 6 hours by 18% and 47% respectively. However, the chlorothalonil removal by the zeolite- complex increased slowly and steadily up to 92% in 96 hours. These findings suggested that zeolite- complex could be applied for effective removal of organic contaminants in the soil and aqueous environment.

Occlusion potential of zeolites for mixed and non-nitrate salts

Occluded 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 KClO 3 and KH 2PO 4 were occluded by mordenite, although they do not establish stable molten state. Their occlusions were confirmed by 27Al NMR spectra, N 2 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 NH 4NO 3 and KNO 3 resulted in co-occlusion of both NH 4NO 3 and KNO 3 by Na–P1 below the melting temperature of KNO 3. 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.

Occlusion and ion exchange in the molten (lithium chloride+potassium chloride+alkaline-earth chloride) salt+zeolite 4A system with alkaline-earth chlorides of calcium and strontium and in the molten (lithium chloride+potassium chloride+actinide chloride) salt+zeolite 4A system with the actinide chloride of uranium

The interaction between molten salts of the type LiCl-KCl-MeCl n (Me=Ca, Sr, U; \(x_{MeCl_n } \)= to 0.45; and x KCl/x LiCl=0.69) and zeolite 4A have been studied at 823 K. The main interactions between these salts and zeolite are molten salt occlusion to form salt-loaded zeolite and ion exchange between the molten salt and salt-loaded zeolite. An irreversible chemical reaction has been observed in the LiCl-KCl-UCl3+zeolite system. The extent of occlusion is a function of the concentration of MeCl n in the zeolite and is equal to 10±1 Cl− per zeolite unit cell, (AlSiO4)12, at infinite MeCl n dilution. The ion-exchange mole-fraction equilibrium constants (separation factors) with respect to Li are decreasing functions of the concentration of SrCl2 and UCl3, but an increasing function of the concentration of CaCl2 in the zeolite. At infinite MeCl n dilution, they are equal to 0.9, 11.9, and 13 for CaCl2, SrCl2, and UCl3, respectively. The standard ion-exchange chemical potentials are equal to −50.0, −84, and −101.1 kJ·mol−1 for Ca2+, Sr2+, and U3+, respectively.

Silver nanowires: inclusion in and extrusion from a mesoporous template.

Silver nanowires both included in and extruded from a purely siliceous mesoporous support have been produced from silver ion containing precursors prepared through dry salt occlusion.

Role of framework on NH 4NO 3 occlusion in zeolite pores

Salt occlusion in zeolites is a unique phenomenon and plays an important role in solid and molten state reactions. To elucidate its mechanism, the NH 4NO 3 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 NH 4NO 3 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 NH 4NO 3 salts were present in the pores of zeolites such as AlPO 4-18, 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 NH 4NO 3. 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.

Occlusion and ion exchange in the molten (lithium chloride-potassium chloride-alkali metal chloride) salt + zeolite 4A system with alkali metal chlorides of sodium, rubidium, and cesium

Interaction between molten salts of the type LiCl-KCl-MeCl (Me = Na, Rb, Cs, xMeCl = 0 to 0.5, xKCl/xLiCl = 0.69) and zeolite 4A have been studied at 823 K. The main interactions between these salts and zeolite are molten salt occlusion to form salt-loaded zeolite and ion exchange between the molten salt and salt-loaded zeolite. No chemical reaction has been observed. The extent of occlusion is a function of the concentration of MeCl in the zeolite and is equal to 11±1 Cl− per zeolite unit cell, (AlSiO4)12, at infinite MeCl dilution. The ion-exchange mole fraction equilibrium constants (separation factors) with respect to Li are decreasing functions of concentration of MeCl in the zeolite. At infinite MeCl dilution, they are equal to 0.84, 0.87, and 2.31 for NaCl, RbCl, and CsCl, respectively, and increase in the order Na<Rb<Cs at identical MeCl concentrations. The standard ion-exchange chemical potentials are equal to −(0.0±0.5) kJ·mol−1, −(0.4±0.3) kJ·mol−1, and −(6.5±0.5) kJ·mol−1 for Na−, Rb−1, and Cs+, respectively.

Molten-salt method for the synthesis of zeolitic materials: II. Characterization of zeolitic materials

Characterization of zeolitic materials synthesized by the newly developed molten-salt method was carried out. Their physicochemical properties were investigated and compared to those of zeolitic materials prepared by the conventional hydrothermal method. The molten-salt method exhibited much less elemental loss during the zeolitization process. The product yield based on the reaction weight was about twice as high in the molten-salt method as in the hydrothermal method. The molten-salt method resulted in zeolitic materials with higher purity, larger contents of alkali metals, lower pH values, and lower cation exchange capacity (higher Si/Al ratio). Salt occlusion also took place in the cavities of the resulting zeolites during the zeolitization of fly ash by the molten-salt method. It seems, therefore, apparent that the high temperature and dry conditions in the molten-salt method lead to zeolitic materials which are somewhat different from hydrothermally synthesized zeolitic materials.

On the reactive occlusion of the (uranium trichloride + lithium chloride + potassium chloride) eutectic salt in zeolite 4A

The interaction between the (uranium trichloride + lithium chloride + potassium chloride) eutectic salt and zeolite 4A has been studied by temperature-resolved synchrotron powder X-ray diffraction, evolved gas analysis and differential scanning calorimetry, between 300 and 900 K. The onset of salt occlusion by the zeolite has been detected at 450 K. Evidence of a reaction between zeolitic water and uranium trichloride, leading to the formation of uranium dioxide, has appeared at 600 K. The uranium dioxide particle size increases from 2 nm at 600 K to 25 nm at 900 K – an indication of their extra-zeolitic location. No appreciable degradation of the zeolite structure has been observed.

Ammonium Nitrate Occlusion vs. Nitrate Ion Exchange in Natural Zeolites

AbstractSeveral salts, such as NH4NO3 and KNO3, can be occluded in natural zeolites through molten salt treatments, which increase the capacity of zeolites to store nutrients in addition to exchangeable cations. Zeolites occluded with NH4NO3 are potential candidates as slow‐release fertilizers. This study focuses on determining the rates of NH4NO3 uptake by natural zeolites from molten salt and on evaluating kinetics of ion release from NH4NO3‐occluded zeolites. The kinetics of ion release from NH4NO3‐occluded zeolites were compared with those of NH+4‐saturated zeolites. NH4NO3‐occluded zeolites were prepared by treatment in molten NH4NO3 at 185°C for different time periods, or at 250°C for 4 h. Uptake of molten NH4NO3 by erionite apparently reached equilibrium after 8 h of treatment at 185°C. The total N uptake by NH4NO3‐occluded zeolites was not related to cation‐exchange capacity but depended on the structural type of the zeolite. Approximately a twofold increase in total N loading capacities of zeolites was achieved through salt occlusion compared with NH+4 exchange from solution. For example, phillipsite exhibited a N loading capacity of 76 g N kg‐1 when treated with molten NH4NO3, but showed a capacity of only 46 g N kg‐1 through NH+4 exchange. A simulated soil solution was used to examine the kinetics of ion release from both NH4NO3‐occluded and NH+4‐saturated zeolites. Occluded NH+4 and NO‐3 were released slowly and steadily as in the case of exchanged NH+4 alone from zeolites during 30‐d treatment in a simulated soil solution. It is evident from this study that salt‐occluded zeolites are potential candidates as slow‐release fertilizers.

Occlusion of KNO 3 and NH 4NO 3 in natural zeolites

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 cm 1 , 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.

ChemInform Abstract: A Route to the Dispersion of Ultrafine Cobalt Particles on Zeolite Na‐ X Through Salt Occlusion and Reduction.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

A route to the dispersion of ultrafine cobalt particles on zeolite Na–X through salt occlusion and reduction

Ultrafine magnetic cobalt particles, encapsulated within a zeolitic host, have been prepared via the seldom-used method of salt occlusion followed by reduction to the metallic state. Powder X-ray diffraction and electron microscopy clearly showed the formation of 150–250 Å cobalt particles which were too large to be contained in the supercage of the zeolite. An increase in cobalt content increases the number of these cobalt particles, but not their size. We thus propose that these particles are encapsulated within locally distorted areas of the zeolite structure. This work demonstrates the clear potential of zeolites as templates or host matrices for the synthesis of ultrafine metal particles.

Hydrothermal aging of cracking catalysts. II. Effect of steam and sodium on the structure of LaY zeolites

The crystal structure analysis of a highly-exchanged LaY zeolite at 660°C, in the presence of steam, shows that there are two La 3+ cations per sodalite cage bridged by two hydroxyl groups which form TOLa(OH) 2LaO T ( T = Si, Al) linkages stretching across the cages. A radial electron distribution study of the structure of partially or completely destroyed LaY zeolites shows that the TOLa bonds are broken, however, the La 3+ ions remain associated in the form of an oxide dimer. Therefore, the mechanism of zeolite aging involves hydrolysis of the TOLa bonds and the transient, local formation of HY zeolite domains which are not stable at high temperature. The occlusion of NaCl salt in the zeolite framework leads to a lower thermal stability. Crystal structure analysis indicates that the linkages involving La 3+ ions in sodalite cages are not present after salt occlusion which may account for the lower thermal stability.

COMPLEX ACTION OF SILVER-FORM CLINOPTILOLITE

By means of chemical analysis, X-ray diffraction and scanning electron micrograph, this article studies complex action which occurs on silver-form clinoptilolite and its meta-glass reacts with solutions of halogenide (except fluoride), sulphide, etc. This complex action includes the "connecting growth" crystallization of the solid sample surface and the internal salt occlusion. Compounded anions have replaceable property, and cations entered into solid sample with the anions also have replaceable property. Complex sequence is S2->I->Br->Cl- and irreversible. The complex anions can be eluted by some oxidizer and the property has important significance for production.

Investigation of NaN 3 salt occlusion in the framework of Y zeolites

The interaction between sodium atoms (obtained by thermal decomposition of NaN3) and acidic OH groups of the zeolite, leading to the elimination of H+ ions, is accompanied by the occlusion of the NaN3 in the zeolitic framework. This salt occlusion process was investigated using X-ray, thermogravimetric, i.r. and visible spectroscopic methods. NaN3 occluded in the zeolite framework does not decompose at 773 K, though this temperature is higher than the decomposition temperature of the pure NaN3. It was found that nearly two N−3 ions per u.c. were occluded in the framework without destroying the crystal structure of the zeolite.

Infrared spectroscopic studies of melt-deposited salt occlusion by zeolites

Sodium nitrate is occluded by the zeolites NaX and NaA. In addition to occluded nitrate, adherent nitrate appears to contribute to the infrared spectra of most zeolite+NaNO3 systems. A lattice mode has been detected for the system NaA+NaNO3, which is interpreted in terms of an ordered occluded phase. Evidence indicates that both occlusion and cation exchange occur in the system NaA+LiNO3. The extent of occlusion of NaNO3 by NaX is much less than by NaA. Interaction between the zeolitic cation and the occluded phase is not significant even when the zeolitic cation is strongly coordinating (e.g. Zn2+). Little, if any, KSCN is occluded by zeolites NaA and NaX, and KSCN appears to react on the internal surface of ZnX.

IR investigation of NH4Y zeolite samples poisoned with sodium vapor

The interaction between sodium atoms (obtained by thermal decomposition of NaN3) and acidic OH groups of the zeolite framework has been investigated by IR spectroscopy. Reduction in band intensities could be observed, its extent depending on the amount of NaN3 and temperature. Impregnated samples showed displacement of the N=N≡N⊖ IR band characteristic of salt occlusion.