Experimental Study on Adsorption of Hexavalent Chromium with Microwave-Assisted Alkali Modified Fly Ash

Coal fly ash, a kind of solid waste generated from coal-fired power stations, can be used as an absorbent for Cr(VI) from aqueous solution. The adsorption characteristics of microwave-assisted alkali modified fly ash to hexavalent chromium had been investigated. Many experimental conditions including pH, contact time, temperature, and fly ash dosage have significant impacts on adsorption performance of modified fly ash. The optimum conditions for the preparation of modified fly ash were as follows: microwave power 600 W, microwave temperature 60 °C, and microwave time 10 min. Batch experiments on adsorption isothermal characteristics of the fly ash modified under the optimal conditions were carried out. The results show that the adsorption of hexavalent chromium ions by modified fly ash is in accordance with the Freundlich and Langmuir isotherm adsorption models, which indicates that the adsorption process is monomolecular adsorption. Environmental-benign utilization of fly ash as low-cost adsorbents in wastewater treatment would bring long-term economic and environmental benefits.