Evaluation of Activated Carbons Prepared from Bioprecursors for the Removal of Cadmium and Chromium (VI)

Trace metals found in industrial effluents are highly toxic pollutants, and these include cadmium and chromium (VI). The objective of this work is to remove cadmium and chromium (VI) on activated carbons, prepared from biomaterials such as nuclei of Ziziphus lotus and coffee grounds. The characterization of adsorbents was performed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results of the characterization showed an important porosity on the activated carbon's surface, with sizes between 6 and 50 mu m. Similarly, the adsorption results showed that the adsorption process is very rapid and that the increase in contact time and temperature improves the efficiency of the Cd and Cr(VI) removal process. Indeed, abatement rates (R%) of 80% for Cr(VI) and 60% for Cd were obtained after 80 minutes of adsorption on activated carbon prepared from Ziziphus lotus, whereas activated carbon obtained from coffee grounds allows a reduction rate of about 50% for Cr(VI) and Cd. Hence, it seems clearly that the activated carbon of Ziziphus lotus is more effective than that of coffee grounds, especially for the Cr(VI) adsorption. The kinetic modeling of the adsorption process followed the pseudo-second-order model, and the Freundlich model has better explained the adsorption isotherm for Cd and Cr(VI). The thermodynamic study showed that adsorption was spontaneous and endothermic.