Abstract: The study on the performance of natural adsorbents like chitosan, saw dust and tea waste in the removal of chromium ion (Cr (VI)) from wastewater has been performed in batch mode. The effects of pH, adsorbent concentration, Cr (VI) concentration, contact time and shaking speed were studied on the removal of Cr (VI) from synthetic wastewater. A comparative study has been done on the adsorption capacities of the three adsorbents for Cr (VI) adsorption. The highest adsorption capacity of 99.257% has been observed with chitosan as adsorbent at optimized conditions. The equilibrium data for the batch adsorption of Cr (VI) onto natural adsorbents have been tested with Langmuir, Freundlich, BET and Dubinin-Radushkevich isotherm models. The mechanism of Cr (VI) sorption by chitosan gave good fits with the Langmuir model with a maximum adsorption capacity of 35.7 mg/g. It has been found that the kinetics of Cr (VI) adsorption onto chitosan can be explained well by the pseudo second order kinetic model. Desorption of Cr (VI) ions from the metal loaded chitosan was maximum at 0.1M of H2SO4 with an agitation speed of 120 rpm and a contact time of 60 minutes. A multiple response method, using the design expert software was applied for optimization of adsorbent dosage, Cr (VI) concentration, contact time, agitation speed % adsorption and % desorption.

Keywords: Cr (VI) adsorption , chitosan, isotherm, kinetics ,saw dust and tea waste.