Zeolites Erionite

Staples, LW. and Card, J.A. (1959) The fibrous zeolite erionite its occurrence. 

Kokotailo, G.T., Sawruk, S., and Lawton, S.L. (1972) Direct observation of stacking faults in the zeolite erionite. American Mineralogist, 57, 439 44. 

Baris YI. 1991. Fibrous zeolite (Erionite)-related diseases in Turkey. Am J Ind Med 19 374-378. 

Another key step was the demonstration by P.B. Weisz and coworkers (3-5) of the shape selectivity of zeolite catalysts related to molecular sieving (1960). This initiated further research in the synthesis of new zeolites as well as industrial applications based on this property. The first commercial shape-selective process, Selectoforming, was developed by Mobil (1968) and allowed the selective cracking of the low octane (n-alkane) components of light gasoline over a natural zeolite (erionite) (6). 

Erzen C, Eryilmaz M, Kalyoncu F, et al. 1991. CT findings in malignant pleural mesothelioma related to nonoccupational exposure to asbestos and fibrous zeolite (erionite). J Comput Assist Tomogr 15 256-260. 

A gas phase process for thymol manufacture using medium pore-sized zeolites (erionite, mordenite, or ZSM-23) as heterogeneous catalyst was developed in 1988. It was reported that reaction temperatures were lower (230-270°C) than in the older liquid phase process. Reaction pressure was reported to be normal or slightly elevated. 

The basic structures of nearly all of the zeolite minerals appear to have been resolved, including the complex structures of laumontite (17), stilbite (39), heulandite (63), and yugawaralite (55). In addition, the relationship of the zeolites erionite and offretite has been delineated further by the work of Kawahara (51) and, in this symposium, by Gard. Zeolite minerals for which structural analyses have not been completed include the widely occurring mineral clinoptilolite and the rarer mineral stellerite, which apparently is related to stilbite. 

As in many procedures of zeolite modification XRD plays an important role as a tool for checking the integrity of the zeolite crystals modified by solid-state exchange. This is particularly true for those solid-solid reactions with zeolites in which hydrohalic gases are evolved. In fact, Clearfield et al. [13] reported lattice damage upon solid-state reaction of H,Na-A with halides. Loss of crystallinity was less severe with H,Na-X Y-type zeolites, erionite, mordenite and H-ZSM-5 proved to be fully resistent even when HF was released [13,22]. 

An 8-membered ring zeolite, erionite, gives a constraint index of 38, 10-membered ring zeolites, ZSM-5 and ZSM-11, give values of 8.3 and 8.7, respectively, while 12-membered ring zeolites, mordenite and REY, give values of 0.5 and 0.4. In this way, the constraint index is a very useful tool for estimating the pore size of zeolites of unknown structures. 

Judging by the differences in iron-contents of crocidolite and chrysotile. Hardy and Aust (1995) proposed that the high iron content of the amphibole asbestos fiber, crocidolite, was the cause of its much greater carcinogenicity than the chrysotile fiber, which, indeed, contains forty times less iron than crocidolite or amosite. However, the fibrous zeolite erionite, also contains much less iron (about 18 times less iron than the amphiboles, and is also much less tightly bound cf. van Oss et al.(1999). As the mechanisms of pulmonary carcinogenesis of amphibole asbestos needles and of erionite needles are remarkably similar, the differences in the iron contents of amphibole and chrysotile asbestos species appear to be irrelevant. 

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