Natural Zeolites in Water Treatment – How Effective is Their Use

Abstract

Additional information is available at the end of the chapter http://dx.doi.org/10.5772/50738 IntroductionNatural zeolites are environmentally and economically acceptable hydrated aluminosilicate materials with exceptional ion-exchange and sorption properties. Their effectiveness in different technological processes depends on their physical-chemical properties that are tightly connected to their geological deposits. The unique treedimensional porous structure gives natural zeolites various application possibilities. Because of the excess of the negative charge on the surface of zeolite, which results from isomorphic replacement of silicon by aluminum in the primary structural units, natural zeolites belong to the group of cationic exchangers. Numerous studies so far have confirmed their excellent performance on the removal of metal cations from wastewaters. However, zeolites can be chemically modified by inorganic salts or organic surfactants, which are adsorbed on the surface and lead to the generation of positively charged oxihydroxides or surfactant micelles, and which enables the zeolite to bind also anions, like arsenates or chromates, in stable or less stable complexes. Natural zeolites have advantages over other cation exchange materials such as commonly used organic resins, because they are cheap, they exhibit excellent selectivity for different cations at low temperatures, which is accompanied with a release of non-toxic exchangeable cations (K + , Na + , Ca 2+ and Mg 2+ ) to the environment, they are compact in size and they allow simple and cheap maintenance in the full-scale applications. The efficiency of water treatment by using natural and modified zeolites depends on the type and quantity of the used zeolite, the size distribution of zeolite particles, the initial concentration of contaminants (cation/anion), pH value of solution, ionic strength of solution, temperature, pressure, contact time of system zeolite/solution and the presence of other organic compounds and anions. For water treatment with natural zeolites, standard procedures are used, usually a procedure in column or batch process. Ion exchange and adsorption properties of natural zeolites in comparison with other chemical and biological processes have the advantage of Water Treatment 82removing impurities also at relatively low concentrations and allows conservation of water chemistry, if the treatment is carried out in the column process [1]. Subject of further academic and industrial research should be to improve the chemical and physical stability of modified zeolites and to explore their catalytic properties, which would allow their use in catalytic degradation of organic pollutants. More careful consideration of their superb metal removal properties and awareness of possible regeneration or further use of contaminant/metal-loaded forms can considerably increase their environmental application possibilities, with a focus the reduction of high concentrations of cations and anions in drinking water and wastewater, for surface, und...

Applicability of Natural Zeolite for NH-Forms Removal in Enzyme-Mediated Calcite Precipitation Technique

“…The ion-exchange behavior of natural zeolite depends on several factors: the framework structure, the ion size, the shape, the charge density of the anionic framework, the ionic charge, and the concentration of the external electrolyte solution [24]. The rate of the ion exchange process using zeolite can be increased by the intensity of the mixed solution and by the augmentation of the concentration and temperature of the solution [30].…”

“…2+ , and/or Ba 2+ ). Al and Si are known as structural cations which develop the framework of the structure with O [22,30]. The ion-exchange behavior of natural zeolite depends on several factors: the framework structure, the ion size, the shape, the charge density of the anionic framework, the ionic charge, and the concentration of the external electrolyte solution [24].…”

Characterization and Utilization of Natural Zeolites in Technical Applications

“…Hence, geological factors control the stability of zeolite phases (i. e. which zeolites form) as well as the type and amount of gangue minerals present and have a strong influence on the quality and applicability in technical processes. Prior to any technical application a detailed characterization of these materials is therefore necessary in order to understand performance and behaviour within any practical application [14,24]. The enormous diversity of zeolites and varying experimental setups and characterization methods make it difficult to compare the results especially when proposed applications are not standardized.…”

“…Large-scale cation-exchange processes for water treatment using natural zeolites were described in the early 1970s, e. g. [13]. Natural zeolites have advantages over other cation exchange materials such as commonly used organic resins, because they are cheap, exhibit excellent selectivity for different cations at low temperatures, are compact in size and allow simple and cost-efficient maintenance in full-scale applications [14].…”

Limitation of the environmental impact of ashes from combustion of sewage sludge by the synthesis of zeolites

“…The CEC values of natural zeolites are in the range of 200-500 meq/100g [38][39]. There are zeolites of higher CEC values, for instance pure hydroxy sodalite has a CEC value of 920 meq/100g [40].…”