Application of Quaternized Activated Carbon Derived from Macadamia Nutshells for the Removal of Hexavalent Chromium from Aqueous Solutions

In this paper, the feasibility of quaternized activated carbon derived from Macadamia nutshells was explored in the removal of hexavalent chromium (Cr(VI)) from aqueous solutions. The amino-modified activated carbon was achieved by cross-linking native Macadamia activated carbon (MAC) with epichlorohydrin and grafting diethylenetriamine and triethylamine (EDT) on the surface and the product was labelled as MAC-EDT. The adsorbent was characterized by Fourier transform infrared spectroscopy (FTIR), Bruemer-Emmett-Teller (BET), scanning electron microscope (SEM) and the CHNS analyzer. The optimum parameters for Cr(VI) removal found were pH(5), contact time (120 min) and sorbent mass (0.10 g) where removal efficiencies were >90% in all cases. Langmuir model fitted the data best and the adsorption capacity was 145.5 mg g(-1) after surface modification with EDT. The Cr(VI) ion was found to be adsorbed more as compared to other anions, and the sorption order was: SO42- < PO43 - approximate to NO3- < Cr2O72. The removal mechanism involved adsorption of Cr(VI) and/or subsequent reduction of Cr(VI) to Cr(III).