Removal of Cr(VI) by modified expanded graphite using Response Surface Methodology

In this study, modified expanded graphite (MEG) was prepared by sequence processes of mixed sucrose/ phosphoric acid solution impregnation, carbonization and insitu H3PO4 activation. MEG was characterized by scanning electron microscopy (SEM), infrared spectroscopy (IR) and X-ray diffraction (XRD). Adsorptive property of MEG as a porous adsorbent for the removal of toxic Cr(VI) from aqueous solution was investigated. Three process parameters namely initial pH value (2.0-6.0), temperature (20-60 degrees C) and initial Cr(VI) concentration (50-150 mg.L-1) was optimized to obtained the best response of Cr(VI) removal using the statistical Box-Behnken design in response surface methodology (RSM). The response surface data indicated maximum Cr(VI) adsorption (99%) with initial 50 mg.L-1 of Cr(VI) concentration at pH 2.0, temperature 25 degrees C. The MEG adsorbent could remove >80% Cr(VI) from aqueous solution with initial metal concentration of 50-80 mg.L-1. Adsorption data for Cr(VI) removal were analyzed according to Langmuir and Freundlich adsorption models and it was found that the Langmuir isotherm model best fitted the adsorption data. Kinetic studies were done and can be described by a pseudo-second order rate equation very well.