The contamination of soils, groundwater, and surface water by hydrophobic organic compounds (HOCs) is currently a significant concern throughout the world because many of these compounds are detrimental to both human health and the environment. The cleaning up of water contaminated with HOCs is one of the most difficult and expensive goals in environmental engineering. Clay minerals are the most important inorganic components in soil for sorption of contaminants: in fact these materials are abundant in soils, they have large exchange capacity, and appreciable internal and external surfaces accessible to organic or inorganic molecules[1–3], but without modification are ineffective stable sorbents for contaminant compounds. For this reason clay minerals have been treated with surfactants: this process not only changes the surface properties from hydrophilic to hydrophobic but also greatly increases the basal spacing of the layers [4]. Organo-clay complexes, have the potential to remove heavy metals and organic pollutants at the same time due to increased adsorption properties, show several promising applications in contamination prevention and environmental remediation, including the treatment of waste effluents, as extenders for activated carbon and as components of clay barriers, for example in clay slurry walls, hazardous waste landfills and petroleum tank forms [5,6]. The mechanisms controlling the sorption of compounds on organoclays are dependent on the type of organic cations forming organoclays [7]. The aim of this research was to develop a matrix capable of removing organic contaminants from aqueous solutions. The montmorillonite (MMT) used in this study was supplied by the Clay Minerals Society as source clay SWy-2-Na-montmorillonite (Wyoming). The chemical composition of MMT is: SiO2 62.9%, Al2O3 19.6%, Fe2O3 3.35%, MgO 3.05%, CaO 1.68%, Na2O 1.53%. The formula of MMT is (Ca0.12 Na0.32 K0.05)[Al3.01 Fe(III)0.41 Mn0.01-Mg0.54 T 0.02][Si7.98 Al0.02]O20 (OH)4, as calculated from its chemical composition. The cation exchange capacity (CEC) is 76.4 cmol+ Kg-1. The surfactant selected for this study is octadecyl-trimethyl-ammonium-bromide (ODTMA) synthesized in the laboratories of University of Basilicata (98.8%). The method adopted for the preparation of organo-modified clay was similar to those described in the literature [8,9]. Montmorillonite, surfactant and organo-modified clay samples were analysed by X-ray diffraction using a Rigaku Rint 2200 powder diffractometer with Cu-Kα radiation and graphite monochromator. The X-ray patterns of the unmodified and modified clay mineral show a basal spacing (d001) of 12.2 Å and 18.7 Å respectively indicating that ODTMA was retained on the MMT. Atrazine was used as sorption model at rate of 0.35 mol Kg-1 organoclay, and retention by surfactant-modified MMT was measured by using the Thermo micro ESI/FT-ICR/MS 7T. Results of chemical analyses confirmed the usefulness of tested retention process on atrazine. At the end of the batch equilibration period, the disappearance of the herbicide from the treatment solution was 76.5% of the initial amount. This amount was considered as retained by the organoclay. Washing of the air-dried organoclay after sorption, returned 20.1% of retained chemical. Release of the herbicide was controlled again after 6 months of equilibration in water giving 29.5 % of the retained atrazine. Therefore, the organoclay was able to strongly retain 53.9% of atrazine used in the treatment. Organoclays modified using quaternary ammonium salts are suitable for waste water cleaning, but these salts could be toxic if released in drinking water. A more concern could receive new natural polymers we are experimenting aiming at the purification of water for human and animal consumption.

WATER PURIFICATION FROM ORGANIC POLLUTTANTS BY USING MICELLE-CLAY SYSTEMS

SCRANO, Laura;LELARIO, FILOMENA;BUFO, Sabino Aurelio
2009-01-01

Abstract

The contamination of soils, groundwater, and surface water by hydrophobic organic compounds (HOCs) is currently a significant concern throughout the world because many of these compounds are detrimental to both human health and the environment. The cleaning up of water contaminated with HOCs is one of the most difficult and expensive goals in environmental engineering. Clay minerals are the most important inorganic components in soil for sorption of contaminants: in fact these materials are abundant in soils, they have large exchange capacity, and appreciable internal and external surfaces accessible to organic or inorganic molecules[1–3], but without modification are ineffective stable sorbents for contaminant compounds. For this reason clay minerals have been treated with surfactants: this process not only changes the surface properties from hydrophilic to hydrophobic but also greatly increases the basal spacing of the layers [4]. Organo-clay complexes, have the potential to remove heavy metals and organic pollutants at the same time due to increased adsorption properties, show several promising applications in contamination prevention and environmental remediation, including the treatment of waste effluents, as extenders for activated carbon and as components of clay barriers, for example in clay slurry walls, hazardous waste landfills and petroleum tank forms [5,6]. The mechanisms controlling the sorption of compounds on organoclays are dependent on the type of organic cations forming organoclays [7]. The aim of this research was to develop a matrix capable of removing organic contaminants from aqueous solutions. The montmorillonite (MMT) used in this study was supplied by the Clay Minerals Society as source clay SWy-2-Na-montmorillonite (Wyoming). The chemical composition of MMT is: SiO2 62.9%, Al2O3 19.6%, Fe2O3 3.35%, MgO 3.05%, CaO 1.68%, Na2O 1.53%. The formula of MMT is (Ca0.12 Na0.32 K0.05)[Al3.01 Fe(III)0.41 Mn0.01-Mg0.54 T 0.02][Si7.98 Al0.02]O20 (OH)4, as calculated from its chemical composition. The cation exchange capacity (CEC) is 76.4 cmol+ Kg-1. The surfactant selected for this study is octadecyl-trimethyl-ammonium-bromide (ODTMA) synthesized in the laboratories of University of Basilicata (98.8%). The method adopted for the preparation of organo-modified clay was similar to those described in the literature [8,9]. Montmorillonite, surfactant and organo-modified clay samples were analysed by X-ray diffraction using a Rigaku Rint 2200 powder diffractometer with Cu-Kα radiation and graphite monochromator. The X-ray patterns of the unmodified and modified clay mineral show a basal spacing (d001) of 12.2 Å and 18.7 Å respectively indicating that ODTMA was retained on the MMT. Atrazine was used as sorption model at rate of 0.35 mol Kg-1 organoclay, and retention by surfactant-modified MMT was measured by using the Thermo micro ESI/FT-ICR/MS 7T. Results of chemical analyses confirmed the usefulness of tested retention process on atrazine. At the end of the batch equilibration period, the disappearance of the herbicide from the treatment solution was 76.5% of the initial amount. This amount was considered as retained by the organoclay. Washing of the air-dried organoclay after sorption, returned 20.1% of retained chemical. Release of the herbicide was controlled again after 6 months of equilibration in water giving 29.5 % of the retained atrazine. Therefore, the organoclay was able to strongly retain 53.9% of atrazine used in the treatment. Organoclays modified using quaternary ammonium salts are suitable for waste water cleaning, but these salts could be toxic if released in drinking water. A more concern could receive new natural polymers we are experimenting aiming at the purification of water for human and animal consumption.
2009
9788875220273
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11563/14188
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