Zeolites

Abstract

Zeolites are a well-defined dass of crystalline natural or synthetic a1uminosilicates with an extensive framework of SiO4 and AIO4 tetrahedra, interlinked in different ways by sharing oxygen atoms. The framework cations are exchangeable. Because of their uniform pore sizes from 0.3 to 0.8 nm, zeolites can selective1y adsorb or reject molecules based on their size and act as molecular sieves. Until 1976 zeolites (mainly type Y) were manufactured only on a relatively small industrial scale for use particularly in sorption and catalysis. Although insoluble in water, zeolite A proved to be an excellent detergent builder. By optimization of the detergent formulation and use of cobuilders, the detergency performance of non-phosphate zeolite-containing laundry detergents can reach that of detergents formulated with sodium triphosphate, the traditional detergent builder. Zeolite NaA is now established as a detergent builder in the U.S., Europe, and Japan with a consumption of more than 700 × 103 t and a production capacity of more than 900 × 103 t in 1991. From an environmental point of view non-detergent applications are much less important. Among the different zeolites type A has been ecologically and toxicologically scrutinized for a number of years because of its increasing importance as a detergent builder. A very thorough investigation of the fate and effects of zeolite A as a detergent builder along its disposal pathway has been made-from domestic piping via communal sewage systems into the various stages of sewage works leading to the final receiving water outlets and, via sludge, on arable land. No indications of any adverse effects in any of these stages were found. It has rarely been possible to realize a desired effect-here a lowering of detergent phosphate content and, in the final analysis, a decrease of anthropogenie phosphate input into our surface waters-with so few and so minor, if any, adverse effects. Health risks or other hazards in connection with preparation, processing, and applicatlon have not been found.