Optimisation of preparation of hazelnut shell activated carbon for adsorption of Cr (III)

The aim of this study was the optimisation of the activated carbon (C) production process by dehydration-carbonisation using concentrated sulfuric acid (H2SO4) from hazelnut shells found locally and readily available agricultural waste and the adsorption of chromium (III) (Cr3) on the activated carbon produced by this method. An adsorption experiment was carried out at conditions of 25 degrees C and initial concentration of 30 mg chromium (III)/l. The optimum process conditions for ensuring maximum adsorption capacity were investigated by means of statistically designed experiments and steepest ascent experiments. The optimum values found were an impregnation ratio of 4.5 ml sulfuric acid/g hazelnut shells, an oven temperature of 50 degrees C, a holding time in the oven of 19.8 h and a maximum adsorption capacity of 14.76 mg chromium (III)/g hazelnut shell activated carbon (HSAC). The surface properties of HSAC were investigated by scanning electron microscopy and Fourier transform infrared spectroscopy and agreed with the outcomes. The adsorption mechanism could be rapid ion exchange and slow chemisorption and/or an outer-sphere complexation at pH 3.5-6.0 during the process.