engleski

Natural zeolites as multifunctional environmental friendly materials

Natural zeolites are safe, environmentally friendly, naturally occurring aluminosilicate minerals. Zeolite was discovered 260 years ago by the Swedish mineralogist A.A.F. Cronstedt. He was the first scientist who described the properties of this class of minerals. Since 18th century, more than 50 different natural zeolite minerals have been discovered. Among them, clinoptilolite, chabazite, modernite and philipsite are the most abundant (available). In the last twenty years, properties of these minerals have generated worldwide interest in their research and diverse applications. Due to their physical and chemical properties, natural zeolites have been using as building stone, as lightweight aggregate and pozzolan in cement and concrete, as fillers in paper, as ion exchangers, in uptake of Cs and Sr from nuclear waste and fallout, as molecular sieves, as soil amendments in agronomy and horticulture, as universal adsorbents (gases, liquids), in the removal of metal ions and ammonia from municipal, industrial, and agricultural waste and drinking waters, as energy exchangers in solar refrigerators, as additives in pharmaceutical industry, and for contaminated land remediation 1. With more than 2000 deposits found globally, natural zeolites are natural plentiful resources, and are inexpensive to mine, since the majority of deposits are found close to the Earth's surface 2. The most important deposits that are being commercially exploited are in United States, Mexico, Ukraine, Slovakia, Italy, Greece, Turkey, Russia, Serbia, Romania, Bulgaria, Georgia, Armenia, and Cuba. The charged inner and outer surface of natural zeolites is available for attraction of oppositely charged ions, due to their adsorption properties. They have a crystal framework structure that is occupied by cations and water molecules. These ions and water molecules can move within the inner structure enabling ion exchange and reversible dehydration. This property is used for removal of metal cations from aqueous solutions. Different shapes and sizes of main channels within the three-dimensional zeolite structure result in higher affinity for some cations over others. If the zeolite channel opening is small compared to the radius of the hydrated cation, more energy is required for this cation to migrate into the channel than for another smaller cation. For this reason, ions with smaller hydrated ionic radii bind in higher quantity on the zeolite particle. This effect is also defined as selectivity of ion exchange. This paper discusses the removal of lead and zinc ions from binary aqueous solutions on natural zeolite clinoptilolite.

natural zeolite ; clinoptilolite ; column method ; binary solutions

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