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a b s t r a c tThe capacities of natural and modified Brazilian bentonite samples as adsorbents to remove hexavalent metal chromium were investigated under several conditions in batch and column methods. The raw material, Ca-bentonite, was modified by anchorament of 3-aminopropyltrietoxisilane (APS) and 3,2-aminoethylaminopropyltrimetoxisilane (AEAPS) in the surface of bentonite sample. This type of new occurrence of bentonite is suitable as a raw material for adsorption process. Adsorption behavior of three bentonite types was strongly depending on pH of adsorbate solution, contact time adsorbent/adsorbate, and initial concentration of Cr(VI). The results were confirmed by column method and reveals that the adsorption process of materials accorded by the Redlich-Peterson, Sips, Dubinin-Radushkevich, and Langmuir isotherm models. The exothermic enthalpic values reflected a favorable energetic process for chromium ions anchored in the material surfaces. The negative Gibbs free energy results supported the spontaneity of three adsorption reactions with Cr(VI) ions.

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In this study, the original interstratified kaolinite/ilite clay sample has been collected from altered basalt in Minas Gerais state, Southeast of Brazil. The natural sample was used in the intercalation process with dimethyl sulfoxide. The efficiency of the natural and modified kaolinite/illite clay in the adsorption of methylene blue was investigated by determining their equilibrium adsorption isotherms at dye concentrations and pH. The phyllosilicate sample and hybrid material were characterized by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The Freundlich expression for adsorption isotherm was applied in order to determine the adsorption capacity to form a monolayer and the constant related to the adsorption intensity. The maximum number of moles adsorbed was determined to be 55.0 and 62.5 mgg-1 for systems methylene blue/kaolinite/ilite and methylene blue / kaolinite/ilite + dimethyl sulfoxide, respectively.