Kinetics and mechanism of Cr(VI) adsorption onto tea-leaves waste

Adsorption equilibrium and kinetic experiments have been conducted in batch mode to evaluate Cr(VI)tea-leaves waste system. The equilibrium data followed the Langmuir adsorption isotherm and the adsorption was viewed Lis a physicochemical reversible process. A unified approach model was used to describe the adsorption system from both equilibrium and kinetic viewpoints. The model satisfactorily described both kinetic and equilibrium data. The adsorption and desorption rate constants were evaluated from the model fittings and were not dependent on initial concentration and adsorbent doses. pH(zpc) of the adsorbent was evaluated as 4.2 +/- 0.1. and below :hat pH the adsorbent Surface is positively charged. Adsorption of Cr(VI) was found highly pH-dependent, and the removal efficiency dropped sharply from 95 to 10% when pH of the system changed from 2 to 5. The surface functional groups of tea-leaves waste (before and after adsorption) were analyzed by Fourier transform infrared (FTIR) and the amine groups were found to take part in the adsorption of Cr(VI). The experimental result inferred that electrostatic attraction between the surface and the species is one of the major adsorption mechanisms for binding metal ions to the tea-leaves waste. (c) 2008 Curtin University of Technology and John Wiley & Sons, Ltd.