https://doi.org/10.15255/KUI.2003.009
Published: Kem. Ind. 53 (10) (2004) 449—458
Paper reference number: KUI-09/2003
Paper type: Review
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Natural Zeolites and the Possibility of their Application in the Pollutant Control in Graphic Industry

M. Rožić, Z. Bolanča and Š. Cerjan-Stefanović

Abstract

Zeolites are microporous crystalline solids with well-defined structures. Generally they contain silicon, aluminum and oxygen in their framework, and cations, water and/or other molecules within their pores. Because of their unique porous properties, zeolites are used in a variety of applications: petrochemical cracking, ion-exchange, and in the separation and removal of gases and solvents. The framework structure contain linked channels, which are of the right size to allow small molecules to enter (Table 1). They are often also referred to as molecular sieves. The ability to sorb certain molecules, preferentially while excluding others, has opened up a wide range of molecular sieving applications. They can remove atmospheric pollutants, such as engine exhaust gases and ozone-depleting CFCs. Zeolites can also be used to separate harmful organics from water. Zeolites are used in water treatment mainly for removal of NH4 + ions from the urban and industrial waste waters, for removal of heavy metal cations from the industrial waste waters, and removal of radio nuclides from nuclear plant waters. Not only natural zeolites but also the surface modified zeolites become more important in the pollution decreasing (Fig. 2). The most widespread natural zeolite is clinoptilolite (Fig. 1) whose deposits are in the porous rocks in Donje Jesenje. The possibilities of the usage of natural zeolites as ionic exchangers and sorbents of low price in the processes of the removal of printing industry pollutant, are presented in the work. Each conventional printing process (offset, intaglio, flexography, and screen printing) can be divided into four major steps: photographic process, platemaking, press and finishing operations (Fig. 3). Printing operations use materials that may affect air, water, and land: certain chemicals involved in printing volatilize, which contributes to air emissions; other chemicals may be discharged to drains and impact freshwater or marine ecosystems; and solid wastes contribute to the existing local and regional disposal problems (Fig. 3). Emissions into the air mainly consist of organic solvents. Some substances may cause unpleasant odors or affect health and the environment. The four top toxic chemicals released, toluene, methyl ethyl ketone, xylene and 1,1,1-trichloroethane, are all the solvents of high volatility. Toluene comprises roughly 70 % of the total chemicals released and transferred by the printing industry. Toluene is used heavily in the intaglio printing as an ink solvent, but is also used throughout printing for cleaning purposes. Toluene can be recovered by sorption, using active carbon, or zeolites. Discharges to water bodies mainly consist of silver, copper, aluminum, chromium, organic solvents and other toxic organic compounds. In photographic processing, (Fig. 4) a used fixative contains higher concentrations of silver than other spent chemicals, usually between 3 and 7 g dm-3 Ag+. The maximum silver concentration in spent rinsewater are 50 mg dm-3. Chemical precipitation, electrolytic recovery units, reverse osmosis and evaporation/distillation are used to reduce silver concentration in spent fixative’s waters. If ammonium is present in waste stream, the ammonium must be removed prior to evaporation/ distillation. This can be done using activated carbon or zeolite. Ion exchange can be used to recover silver from rinse waters. Typical wastestreams of platemaking operations include: damaged or used plates, wastewaters containing acids, alkalis, heavy metals, solvents, plate coatings, developers and rinse waters. Metal-containing effluents from the platemaking operations for offset and intaglio printing (Figs. 3, 5A, 5B), can be treated by applying method of filtration using zeolites.

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Keywords

clinoptilolite, photographic processes, offset, intaglio