Adsorption of anionic dyes monoazo and diazo using organo-bentonites

Adsorption of orange and yellow dyes, containing mono- and di-azoic groups, respectively, were studied by the use of a natural and organo-bentonites, which were obtained by treatment with hexadecyl-trimethyl-ammonium bromide (Br-HDTMA). Two different bentonites from Argentina were used. X-ray diffraction, UV–visible spectrometry, infrared spectrometry and thermal analysis were used for the characterizations. The results were interpreted by using isotherms that fit properly to the mathematical model of Langmuir. The structural and physicochemical properties of the clay, and the arrangement of hexadecyl-trimethyl-ammonium cation (HDTMA+) into the interlayer of the smectites, the main clay mineral composition of the bentonites, were responsible for the retention of dyes. The retention of the azo dyes not only increased with the HDTMA+modification of the bentonites but also depended on the clay mineral (smectite types) composition of the pristine bentonite.