Geoökologisches Kolloquium WS 2002/03

All lecture dates

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Prof. Thomas Armbruster
University of Bern, Switzerland
Thursday, 28.11.2002 16:15 H6

Natural Zeolites: From Structure to Applications

Still fifty years ago natural zeolites mainly from vugs and fissures of volcanic rocks were considered a rare curiosity of nature. About 100 years ago chemists recognized that these minerals with a tetrahedral framework structure, characterized by internal porous space in form of cavities and connecting channels, can be used for ion exchange, molecular sieving, and catalytic reactions. Thus in the 1950s the chemical industry became engaged in the synthesis of these minerals. The industry aimed for chabazite but the synthesis failed and instead the most important synthetic zeolite LTA (Linde Type A) was produced. Simultaneously, geologists discovered huge deposits of natural zeolites mainly in altered volcanic tuffs. Whole mountain ranges on all continents consist of clinoptilolite, phillipsite, chabazite, and analcime with zeolite concentrations above 60%. Since this discovery there is a continuous competition between the pure but expensive synthetic products and the \'dirty\' but inexpensive natural zeolites. About 3.6 Mio tons of natural zeolites are annually produced. In contrast, 1.3 Mio tons of synthetic zeolites are annually consumed for detergents, catalysts, desiccation, and separation. Main applications for natural zeolites are as cat litter, soil conditioner, animal feed addition, ion exchanger for industrial-, agricultural-, and municipal- wastewater treatment, absorber of Sr and Cs radioisotopes in the nuclear industry and for clean up of nuclear accidents (Chernobyl), and soil replacement (ZEOPONICS) in horticulture. Even veterinary and medical applications are under investigation. ENTEREX is an anti-diarrheic drug for humans developed natural zeolites. In general, products from each natural zeolite deposit have a different favorable application depending on structure and chemistry of the zeolite. A sodian zeolite is not good for potable water production or horticultural applications but excellent for ammonia, Cs, Sr, Pb, Cd exchange in wastewater. A potassian zeolite is favorable for soil amendment whereas a calcian zeolite is excellent for animal feed addition. The mechanical properties are of special interest for cat litter applications. Not only the benefits of the porous structure are used. Natural zeolites from altered volcanic tuffs are fine crystalline (about 1 mm) - also responsible for their late discovery - and thus possess a large external surface of high activity. In modern applications such zeolites are surface treated (SMZ: Surface Modified Zeolite) with organic molecules (e.g. HDTMA) used for retention of harmful anions, cations, and non-polar organics such as PCE\'s and benzene in polluted industrial areas.

The lecture gives a short introduction into the formation of zeolite deposits, explains the structural principles of zeolites, and discusses the role of structure and chemistry for the various applications.



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