Zeolite genesis

The identification of a specific zeolite species with a particular genesis or environment of formation is very difficult if natural mineral occurrence is used as the sole criteria. Most alkali zeolites are found at one place or another in most low temperature geological situations. Various authors have cited various physical and chemical factors which would control the sequence or particular species of alkali zeolite found in nature. Silica and alkali activities in solution are of great importance in surface and buried deposits (Sheppard and Gude, 1971 Honda and Muffler, 1970 Hay, 1964 Coombs, t al.. 1959 Read and Eisbacher, 1974). 

The section on crystallization comprises zeolite synthesis, kinetics and mechanism of formation, stability relationships, recrystallization processes as well as the genesis of natural zeolites. Recent advances in this field have been surveyed, and some new perspectives have been outlined in the review by E. M. Flanigen. Most of the studies in this field are still empirical because of the complexity of the systems involved. Considerable progress has been made, however, towards a better understanding of the processes and mechanisms governing zeolite crystallization. It is not unreasonable to expect that conditions for synthesizing new zeolite structure types can eventually be predicted. 

Let us consider how H+M-M+ is formed, using the scheme for thermal genesis of the active sites and the spectra in Figure 1. On adsorption of Y,Y-dimethylaniline in zeolite 3 in the dark, the 540-600-nm band is observed only in the samples heat treated at 350°, 450°, and 550°C—i.e., when H+M-M+ formation is preceded by formation of both primary MH+ and M+ products. The intensity of bands shows that the most favorable conditions for H+M-M+ formation occurred after zeolite pretreatment at 550°C when the excess M+ cation radicals (430-470 nm) were found together with the H+M+-M+ product. When the samples were treated at 350° and 450°C, all M+ cation radicals reacted. 

Recent research on the elementary steps during preparation of zeolite-supported metals has helped to understand the genesis of these particles in considerable detail. For the best studied systems the goal of preparing catalysts by design has been achieved (69-77). 

The finely crystalline zeolitic matrix of tuffs cements the other non zeolitic particles and is responsible for the overall mechanical properties of the material. The compactness and the consequent physical-mechanical properties are somewhat variable as they are function of various parameters, such as mineral composition, tuff genesis, and original conditions of the deposit, especially as regards looseness of the parent material, grain size distribution, and others. Table 3 summarizes some data on unit weight, y, porosity, P, and uniaxial compressive strength, a, of a few tuff samples and other stone materials. 

Film control can be significant (i) when concentrations in the contacting solutions arc small (less than 10"5M is a rule of thumb estimate), or (ii) in the pores of a pelletised zeolite created by geological genesis or the industrial forming of an agglomerate of small crystallites. It also is of importance in the theoretical assessment of column performance. 

Kermarec M, Olivier D, Richard M, Che M and Bozon-Verduraz E (1982), Electron paramagnetic resonance and infrared studies of the genesis and reactivity toward carbon monoxide of NY ions in a NiCa-X zeolite , J Phys Chem, 86, 2818. 

Genesis of Gallosllicates with ZSM-5 Structure. Insertion of Ga and Zeolitic Properties at Various Steps of Crystallization... 

L. B. Sand As mentioned in the text, these lithium-containing synthetic zeolites do not occur in nature, so experimental data do not apply to the problem of genesis. The synthesis of Na-mordenite at low temperature (75°C) could be of some significance, but a great deal of experimental data are required to apply to the interpretation the conditions for formation in a natural deposit. 

Ye, P., Sjbberg, E and Hedlund, J. (2014) Nanocomposite MFI zeolite-alumina membranes via pore-plugging synthesis genesis of the zeolite material. Microporous Mesoporous Mater., 192, 14-17. 

Pe-Piper (2000) Pe-Piper, G. Mode of occnrrence, chemical variation and genesis of mordenite and associated zeolites from the Morden area. Nova Scotia, Canada Canadian Mineralogist 38 (2000) 1215-1232... 

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