Removal of Toxic Metal Cr(VI) from Industrial Wastewater Using Sawdust as Adsorbent: Equilibrium, Kinetics and Regeneration Studies

Chromium is abundant in nature and has a dominant presence in most of the effluent streams as compared to other heavy metal ions. The presence of highly toxic and carcinogenic hexavalent chromium (Cr(VI)) in effluent streams is a major environmental issue. The electroplating and tannery industry effluents are the major source for the Cr(VI) production in wastewater streams. The present work deals with the determination of Cr(VI) removal capacity from synthetically prepared industrial effluent of electroplating and tannery industries using sawdust which is a low cost adsorbent. In the present study, batch experiments are carried out for an initial Cr(VI) concentration ranging from 50 – 500 mg l -1 . Experimental results demonstrate that the sawdust adsorbent has a significant capacity for adsorption of Cr(VI) from wastewater streams. The effect of various parameters such as pH, contact time, adsorbent amount, and initial Cr(VI) concentration for the adsorption of Cr(VI) on sawdust is investigated. The maximum adsorption of Cr(VI) on sawdust is obtained at pH 1. The equilibrium time obtained is 1050 min for Cr(VI) adsorption on sawdust. The equilibrium data for the adsorption of Cr(VI) on sawdust is being tested with various adsorption isotherm models such as Langmuir, Freundlich, Redlich-Peterson, Koble-Corrigan, Tempkin, DubininRadushkevich and Generalized equation. The Langmuir isotherm model is found to be most suitable for the Cr(VI) adsorption using sawdust. The maximum adsorption capacity obtained using the Langmuir isotherm model is 41.5 mg g -1 at pH 1. The dimensionless equilibrium parameter, RL, signifies a favorable adsorption of Cr(VI) on sawdust adsorbent and is found to be between 0.00453 and 0.0435 (0 < RL < 1). Various kinetic models such as pseudo first-order, second order and Elovich model are used to evaluate the mechanism of adsorption of Cr(VI) on sawdust. The adsorption process follows second order kinetics and the corresponding rate constants, for initial Cr(VI) concentration ranging from 100 – 400 mg/l, is found to be 3.39 × 10 -3 to 4.3 × 10 -4 g mg -1 (min -1 . Desorption of Cr(VI) from sawdust using acid and base treatment exhibit higher desorption efficiency by more than 95%. A feasible solution is proposed, for the disposal of contaminant (acid and base solutions) containing high concentration of Cr(VI) obtained during desorption process. The present work also includes the effect of