Adsorption characteristics of brilliant green dye on kaolin

Experimental investigations were carried Out to adsorb toxic brilliant green dye from aqueous medium using kaolin as an adsorbent. Characterization of kaolin is done by measuring: (i) particle size distribution using particle size analyzer, (ii) BET surface area using BET Surface analyzer, and (iii) structural analysis using X-ray diffractorneter. The effects of initial dye concentration, contact time, kaolin dose, stirring speed, pH and temperature were studied for the adsorption of brilliant green in batch mode. Adsorption experiments indicate that the extent of adsorption is strongly dependent on pH of solution. Free energy of adsorption (Delta G degrees), enthalpy (Delta H degrees)and entropy(AS')changes are calculated to know the nature of adsorption. The calculated values of Delta G degrees at 299 K and 323 K indicate that the adsorption process is spontaneous. The estimated values of Delta H degrees and Delta S degrees both show the negative sign, which indicate that the adsorption process is exothermic and the dye molecules are organized on the kaolin Surface in less randomly fashion than in solution. The adsorption kinetic has been described by first-order, pseudo-second-order and intraparticle-diffusion models. It was observed that the rate of dye adsorption follows pseudo-second-order model for the dye concentration range studied in the present case. Standard adsorption isotherms were used to fit the experimental equilibrium data. It was found that the adsorption of brilliant green on kaolin follows the Langmuir adsorption isotherm. (C) 2008 Elsevier B.V. All rights reserved.