STUDIES ON ADSORPTION KINETICS OF DIHYDRIC PHENOLS ON ACTIVATED CARBON

Abstract

Biological processes are not always successful due to long term biodegradation, and therefore physico-chemical methods have been widely adopted in treatment of wastewaters. The present research work investigates the behaviour of two of the three isomeric dihydroxy benzenes. (dihydric phenols) viz., Catechol and Hydroquinone, in single solute batch adsorption reactors. The removal of dihydric phenols from aqueous solutions by adsorption on Industrial Grade Granular Activated Carbon (IGGAC) and Laboratory Grade Granular Activated Carbon (LGGAC) have been investigated. The effect of different parameters such as adsorbent dose, initial adsorbate concentration, temperature, particle size and contact time for the reaction mixture has been studied. Results indicate that at low adsorbate concentrations, small particle size of adsorbent, pH range from 3.0 to 5.0 and low temperatures favour the removal of dihydiic phenols. 100% removal of dihydric phenols was achieved at an initial adsorbate concentration of 50 mgt-' at 30°C and pH 5.0. The shifting of the pH value from acidic to alkaline range is due to the complexation and ion exchange taking place in the adsorbate - adsorbent system. The adsorption behaviour of dihydric phenols is influenced by the position of hydroxyl group on the benzene ring. The adsorption capacities, of each component onto activated carbon is described by the Freundlich and Langmuir models. The adsorption capacities (Kf) of IGGAC are 5.50 mgg-' and 8.02 trigg-1; while Kf values for LGGAC are 2.22 mgg' and 2.55 mge respectively for Catechol and Hydroquinone removal. iv The results indicate that the mass transport mechanism is controlled by Intraparticle diffusion occuring in the micropores and the micropores of the adsorbent. The diffusion rate parameters lc, k2 and k3 have been calculated for each compound representing the adsorption mechanism in batch systems. Experiments were also conducted with chemically regenerated exhausted carbon, for Catechol and Hydroquinone removal efficiency. The regenerated carbon has about 95% of the original removal efficiency.