Cadmium removal from aqueous solution using microwaved olive stone activated carbon

Contamination of natural aquatic ecosystems by wastewater containing heavy metals is a major environmental and human health issue. The removal of heavy metals using adsorption techniques with microwave-irradiated low-cost adsorbents has a few numbers of studies. In this study, the removal efficiency for cadmium (Cd2+) from aqueous solution using olive stone activated carbon (OSAC) prepared by microwave was investigated. Central composite design (CCD) with response surface methodology (RSM) was applied to evaluate the interaction and relationship between operating variables (i.e., radiation power, radiation time, and impregnation ratio), and to develop the optimum operating condition. Equilibrium isotherms in this study were analyzed using the Langmuir and Freundlich. Kinetic data were obtained and analyzed using pseudo-first-order and pseudo-second-order equations. Based on statistical analysis, Cd2+ removal model proved to be significant with very low probability values (<0.0001). The surface characteristics of the AC prepared under optimized condition were examined by scanning electron microscopy and Fourier transform infrared spectroscopy. The optimum conditions obtained were 565 W radiation power, 7 min radiation time, and 1.87 impregnation ratio. This resulted in 95.32% removal of Cd2+ and 85.15% of OSAC yield. The process via microwave requires significantly lesser holding time as compared to conventional heating method to produce activated carbon of comparable quality. The prediction results fitted well with experimental findings. The adsorption isotherm data fitted the Langmuir isotherm well, and the monolayer adsorption capacity was found to be 11.72 mg/g. Microwaved olive stone can be used for the efficient removal of Cd2+ from contaminated wastewater. (C) 2013 Elsevier Ltd All rights reserved.