Erionite composition

Figure 33a. Alkali zeolites as a function of their compositions in Al-Si-(Na,K)2 coordinates assuming Na-K end-members. Nat = natrolite Anal = analcite Ph = phillipsite Er = erionite F = feldspar S = stilbite ...

A novel class of crystalline, microporous aluminophosphate phases has been discovered. It represents the first class of molecular sieves with framework oxide compositions free of silica. The new class of materials encompasses some fourteen reported three-dimensional microporous framework structures, and six two-dimensional layer-type structures. The three-dimensional structures include structural analogues of the zeolites sodalite and erionite-offre-tite. The novel phases can be synthesized hydro-thermally in the presence of organic amines and quaternary ammonium templates. The template is entrapped or clathrated within the crystallizing aluminophosphate network. After thermal decomposition of the template the three-dimensional molecular sieves have the general composition of Al303 1.0 ... 

The gel was crystallized in closed containers to prevent evaporation loss. Crystallization time ranged from 1 to 5 days depending on gel composition and crystallization temperature. Figure 1 shows the ranges of gel composition where the product is substantially pure erionite. The boundaries are not sharp but rather represent areas of decreasing erionite crystallinity in the product. 

Chemical Properties Si/Al ratio (used to be Si/ Al>2.4 Si/Al >3.0 Si/(A1- -Pe)>2.9 for erionite) is no longer a criteria for discrimination between erionite and offretite, because of the extensive compositional overlap that exists between the two species. However, the Si-Al content in the tetra-hedra framework is the major control on the unit cell volume dimensions in erionite. In addition, Mg cation is a major factor in controlling the crystallization of the mineral species. 

Natural erionite, synthetic nonfibrous zeolite with the composition of erionite, and crocidolite type asbestos were tested at a concentration of 10mg m inhalation in rats. Pleural mesotheliomas were found in 27 of 28 rats exposed to erionite one pulmonary and one pleural tumor were found in 28 rats exposed to synthetic zeolite, and one lung carcinoma was reported in rats exposed to crocidolite. 

Changes in concentrations in the liquid phase of Na,K gels during erionite crystallization are illustrated by Figure 1, where the continuous curves refer to the gel obtained from the mixtures of silicate and aluminate solutions, and the dashed curve represents the gel prepared from silica sol. In both cases, the total composition of initial mixtures is the same (7.1 Na20 2.8 K20 A1203 25.6 Si02 433 H20). Points of the axis of ordinates correspond to the component concentrations in the initial mixtures. 

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