Linear and Non-linear Modelling of Kinetics and Equilibrium Data for Cr(VI) Adsorption by Activated Carbon Prepared from Piliostigma reticulatum

Activated carbon has been found to be useful for purification of liquids and gases via adsorption. Majority of the activated carbon which is utilized in our environment is imported and not produced locally. Activated carbon was prepared from the popular Sahel African plant; Piliostigma reticulatum and used for the extraction of hexavalent chromium [Cr(VI)] molecules from aqueous medium. The Piliostigma activated carbon was characterized using X-ray diffraction, scanning electron microscopy and Fourier transform infrared spectroscopy. The efficiency of this adsorbent to remove Cr(VI) molecules from aqueous medium was investigated at different initial concentrations, pH, contact time and adsorbent dosage. Kinetic studies showed that the adsorption process was described by pseudo-second order kinetic model and the equilibrium modelling results fitted best the Freundlich model. The maximum amount of uptake capacity achieved at pH 1.5 was 3.92 mg/g at equilibrium time of 20 min. The piliostigma activated carbon shows potential of being an environmentally friendly adsorbent for Cr(VI) extraction from contaminated water. Piliostigma reticulatum which is grown freely on the African continent can serve as a viable raw material for this purpose.