Handbuch Europarecht Band 3 Beihilfe- und Vergaberecht
Band 3 behandelt das hochaktuelle Beihilfe- und Vergaberecht. Nach der Darstellung der systematischen Grundstruktur des Beihilfenverbotes werden die einzelnen Beihilfeformen aufgezeigt. Ein Schwergewicht bildet dabei, inwieweit die Erbringung von Leistung
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V.A. NIKASHINA and B.F. MYASOEDOV Vernadsky Institute o/Geochemistry and Analytical Chemistry RAS, Kosigin str. 19 Moscow 117975 Russia
Abstract. Various chemical methods for the modification of zeolites, the properties of modified zeolites and their applications for environmental protection are discussed. Experimental data on obtaining organozeolites for water decontamination and ferritised zeolites for soil remediation are presented.
1.
Introduction
The growing ecological problems and the demands of industry for ion-exchange materials have encouraged the intensive study of the properties of natural zeolites as low-price ion-exchangers [1-3]. Presently, the areas of applications of natural zeolites have been well defmed. However, their use can become more efficient after chemical modification, especially in those cases when the zeolites acquire new valuable properties, while retaining their original ones. An essential number of works in the literature is dedicated to the chemical methods of surface modification of inorganic carriers with various substances [4]. Let us consider the chemical modification methods of the zeolites in detail.
2.
Chemical modification methods for natural zeolites
The modification methods for natural zeolite can be classified into 2 large groups: modification using organic and inorganic compounds. 2.1
MODIFICAnON USING INORGANIC COMPOUNDS
Modification using inorganic compounds is performed by: 335
P. Misaelides et al. (eds.), Natural Microporous Materials in Environmental Technology © Kluwer Academic Publishers 1999
336 •
•
2.2
ion-exchange; in this case, the zeolites are transformed into their monocationic form (e.g., H+, K+, Cu2+, NH/, etc.) by treatment with salt solutions or acids. As a result of this modification, the ion-exchange selectivity and the molecular-sieve and adsorption properties of the zeolites change [5-8]. treatment using solutions of inorganic substances in the absence or in the presence of an oxidant to change the zeolite surface properties [6, 9, 10, 17, 24]. MODIFICATION USING ORGANIC COMPOUNDS
The modification using organic compounds is performed by ion-exchange method as well as by • treatment with simple organic cations (e.g., tetramethylammonium, tetraethylammonium, etc.) to impart hydrophobicity to the zeolite surface [11-13]. Such a sorbent starts to effectively hold organic substances. • treatment with more complex organic substances (e.g., water-soluble polyamines). In this case, the zeolite surface becomes hydrophobic and the zeolites also acquire anion-exchange properties [13-15]. Unfortunately, data on the extent of preservation of the original zeolite cation-exchange properties are not found in the literature.
3.
Application of modified zeolites
As is evident from the foregoing, after modification the zeolite acquire properties suitable for handling ecological problems. Thus, for example, Tarasevich et al. [9,10] obtained by treatment of the zeolite with solutions of Mn2+ and KMn0 4 a sorbent with high afrmity for Mn2+ and Fe2+ and us
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