Batch Studies for the Removal of a Hazardous Azo Dye Methyl Orange from Water through Adsorption on Regenerated Activated Carbons

Abstract

The study of the performances of regenerated activated carbons for the adsorption of MO (methyl orange) in an aqueous medium was carried out with the aim to evaluate the adsorption capacities of these activated carbons. Three regenerated activated carbons issued from the unit of oil treatment of the thermal power station of Dibamba (Cameroon)-DPDC (Dibamba Power Development Company) were obtained thermally and chemically. These three samples (namely CAR 400 °C (chemical regenerated activated carbon at 400 °C), CAR 700 °C (physical regenerated activated carbon at 700 °C) and CAR 900 °C (physical regenerated activated carbon at 900 °C)) and the non-used one CA were characterized by iodine number, XRD (X-ray Diffraction) and FTIR (Fourier-transform infrared spectroscopy). MO adsorption tests were performed in batch mode; this technique allowed the study of the influence of the parameters such as: the contact time, the initial’s MO concentration and the pH. Moreover, different kinetic models (first-order, pseudo-second-order and Webber and Morris intra-particle diffusion) and adsorption isotherms (Langmuir and Freundlich) are used for the evaluation of adsorption capacities. The physicochemical characterization of these adsorbents showed that they were micro-porous (iodine value: 600 mg/g) and strongly crystallized according to their regeneration pathways. The influence of the parameters revealed that the adsorption of MO is the most favorable for concentrations from 5 to 25 mg/L (for materials CA and CAR 400 °C) and 10 to 25 g/L (for materials CAR 700 °C and 900 °C); and that it was maximum in acid medium (at pH = 3 on the materials CA, CAR 400 °C, CAR 900 °C and at pH = 5 on the material CAR 900 °C). The modeling of the adsorption kinetics of MO has revealed the conformity of the kinetic model of pseudosecond-order and intra-particle diffusion for some of these materials. The study of isotherms has shown that the Langmuir isotherm best describes the adsorption of MO on most of these adsorbents.