The removal of anionic dyes from aqueous solutions in the presence of anionic surfactant using aminopropylsilica--a kinetic study.

In this study, the aminopropyl-silica (Sil-NH(2)) was used to adsorb a yellow- and a red-dye from aqueous solutions at pH 4.0. New data concerning the influence of the anionic surfactant SDS on the adsorption data was obtained. All interactions occurred below the cmc values of the Sil-NH(2)/anionic dyes aggregates. A rise of temperature accelerates the mass transfer of the red-dye into the Sil-NH(2) surface, while the yellow-dye adsorption decreased. The presence of SDS increased the adsorption quantities in relation to the temperature increasing. The exception is observed for the yellow-dye adsorption at 55 degrees C. So, it is suggested that the chemical structure of the dye, as well as the presence and position of its sulfonate groups are important factors that affect the anionic dye/SDS aggregations and the adsorption quantities. The solid-phase interactions of dyes data present good fittings to the Avrami kinetic model, where from two to four kinetic regions were found, taking into account the variations of the contact time and temperature. The presence of several values of Avrami constants, namely k(Av) and n, has been attributed to the occupation of both the surface and the internal adsorption sites of the aminopropyl-silica.