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A quantitative thermoanalytical determination of mixture compositions is extremely difficult if there is a partial or full overlapping of the temperature ranges of the thermal transformations, and a proximity of the quantitative characteristics of the weight changes is also observed. A method of quantitative analysis of such a system is offered, based on the calculation of differences in the regularity of rate variation of the thermal transformations of the separate mixture components. The principle of distinguishing temperature intervals with maximum differentiation of thermal effects and methods of calculation of the quantitative mixture composition is shown. Examples of determination of the mineral compositions of zeolite-bearing rock are given.
Abstract
The ion-exchange process on columns filled with granulated zeolites is determined by several physico-chemical parameters. The influence of these parameters (zeolite type, concentration of exchangeable ions in solution, temperature, flow rate, etc.) on the kinetics of ion-exchange process was studied by measuring the Sr2+ ion concentration in solution before and after passing through a column filled with various granulated zeolites (zeolite 13X, zeolite A and synthetic mordenite). Using the experimental technique of radioactive labeling by89Sr, the distribution of Sr2+ ions in column fillings were also determined. From the results obtained, the optimal conditions for the most efficient removal of strontium ions from solutions using granulated zeolites can be defined.
Abstract
Zeolites from Nižný Hrabovec (Slovak Republic) were, modified with solutions of NaOH. The changes of zeolites in the temperature range 20–1200 °C were studied by thermal analysis (DTA, TG, ETA), X-ray analysis and REM analysis. Thermal analysis showed that the process of dehydration started between temperatures 20 and 600 °C, over this temperature the dealumination and structural changes have taken place. X-ray analysis and REM analysis showed the structural changes of natural zeolites and gradual loss of cristallinity of the chemically modified zeolites.
Abstract
The cure kinetics of epoxy resin and epoxy resin containing 10 mass% of natural zeolite were investigated using differential scanning calorimetry (DSC). The conformity of the cure kinetic data of epoxy and epoxy-zeolite system was checked with the auto-catalytic cure rate model. The results indicated that the hydroxyl group on the zeolite surface played a significant role in the autocatalytic reaction mechanism. This group was able to form a new transition state between anhydride hardener and epoxide group. The natural zeolite particles acted as catalyst for the epoxy system by promoting its curing rate.
component for dehydrogenation/hydrogenation provided by a noble metal, basically platinum or palladium [ 1 , 2 ] and an acid function generated by zeolites like mordenite and ZSM-5 for isomerisation/cracking [ 3 , 4 ]. The hydroisomerization mechanism is
Abstract
We report here on the effect of nitric acid solutions on the structural stability and ion-exchange properties of a series of natural and synthetic zeolite molecular sieves. The implications of this work for the industrial application of zeolites in acidic aqueous systems are discussed.
Abstract
Fixation of some fission products and actinide elements from aqueous solutions on zeolite was investigated. Studies showed that the interaction between the radionuclides and zeolite followed the exchange and the adsorption mechanisms. The relative importance of each depends on the type, the nature, and the size of the radioelement.
Abstract
The possiblity of the use of granulated zeolites for the removal of gadolinium ions from solutions has been investigated. Measurements of gadolinium ion concentrations in solutions and of the distribution of gadolinium ions in column filligns (granulated zeolites), after passing the solution through columns filled with various granulated zeolites (zeolite 4A, zeolite 13X and synthetic mordenite), have shown that gadolinium ions can be effectively removed from nearly neutral or acidic solutions using granulated mordenite. The influency of pH, column filling and the flow rate of the solution through the column on the efficiency of gadolinium ion removal and on the distribution of gadolinium ions in the columns has been investigated. On the basis of the results obtained, the conditions for the most efficient removal of gadolinium ions from solutions have been obtained.
Thermal behaviour of pure LiN3, NaN3, CsN3 and their mixture with the respective LiY-FAU, NaY-FAU, CsY-FAU zeolite was investigated by means of thermogravimetry and IR spectroscopy. Thermodesorption of CO2 was applied to compare the basicity of the alkali ionexchanged Y zeolites. Two of the investigated systems, the NaN3/NaY-FAU and the CsN3/CsY-FAU gave single, well defined and reproducible azide decomposition features rendering these samples to apply as catalyst precursors for preparation of zeolite with basic character.
Abstract
Some Hungarian zeolites have been studied by Mössbauer spectroscopy. It has been found that Fe3+ ions substitute for Si4+ in tetrahedral position, while Fe2+ ions are chargecompensating cations in octahedral sites.
