Kinetic and Equilibrium Studies of Cr (VI) Removal from Aqueous Solutions using Activated Neem Bark

Abstract

Hexavalent chromium [Cr(VI)] has a dominant presence in most of the effluent streams as compared to other heavy metal ions coming out from the different industries such as metal finishing, tannery, electroplating, etc. Due to its carcinogenic and toxic nature, it is considered as one of the most important environmental problems. The solution for this problem is a cost effective and eco-friendly treatment technique. Various treatment techniques such as chemical precipitation, ion exchange, membrane separation, electro-coagulation and chemical reduction are available to reduce the contamination of Cr(VI) in the effluent streams. These techniques are not eco-friendly and economically viable for the large volume of wastewater treatment. Adsorption using low cost adsorbents is found to be one of the cost effective technique for Cr(VI) removal from the effluent streams. In the present study, a waste biodegradable material, neem bark, is used. This neem bark is activated using concentrated sulphuric acid (98 wt%) and is used as an adsorbent for Cr(VI) removal from aqueous solutions. Batch adsorption experiments were conducted for determining the performance of activated neem bark for removal of Cr(VI). The effect of various important parameters such as effect of contact time, initial Cr(VI) concentration and dosage of adsorbent for the removal of Cr(VI) using activated neem bark adsorbent are studied. The kinetic studies show 70% removal of Cr(VI) using activated neem bark as an adsorbent while keeping 100 mg/L of initial Cr(VI) concentration. The equilibrium data for the adsorption of Cr(VI) on activated neem bark is being tested with Langmuir isotherm model and Freundlich isotherm model. It is observed that it is following the Langmuir isotherm model and the corresponding adsorption capacity of activated neem bark is 26.95 mg/g. Pseudo first-order and second-order rate kinetic models are used to evaluate the mechanism of adsorption of Cr(VI) on activated neem bark. It is observed that the adsorption of Cr(VI) on activated neem bark follows second order kinetics.