Removal of Cr(VI) from Wastewater using Fly ash as an Adsorbent

Cr(VI) is a highly toxic metal ion and considered a priority pollutant released from various chemical industries. Treatment methods to remove Cr(VI) from water and wastewater include chemical precipitation, ion exchange, membrane separation, electro-coagulation and reduction. These methods are not economically viable for large scale treatment of wastewater that is rich in Cr(VI). Adsorption is a most popular treatment method for the removal of Cr(VI) from industrial effluents. In the present study, fly ash is used as an adsorbent for Cr(VI) removal from aqueous solutions. Fly ash is activated by giving heat treatment and with the use of concentrated sulfuric acid (98% w/w). There is no significant increase in the percentage removal of Cr(VI) with activated fly ash. Batch adsorption studies exhibited that the fly ash has a significant capacity for adsorption of Cr(VI) from aqueous solution. The effect of important parameters such as pH, contact time, initial Cr(VI) concentration and adsorbent dosage is studied. Results indicate that the maximum adsorption of Cr(VI) is found to be 21 mg/g at low values of pH in the range of 1-3. The obtained equilibrium data is tested with Langmuir, Freundlich and Koble-Corrigon isotherms. The experimental equilibrium data fits well with the Langmuir-Freundlich model. The adsorption process follows second order kinetics. Flyash shows a higher desorption efficiency by more than 95% for the removal of Cr(VI).