Kinetics of the Adsorption of Anionic and Cationic Dyes in Aqueous Solution by Low-Cost Activated Carbons Prepared from Sea Cake and Cotton Cake

Abstract

Activated carbons prepared from shea cake (CA-K) and cotton cake (CA-C) were investigated for removal of four dyes in aqueous solutions (0 – 200 mg/L): Reactive Black 5 (RB5), Methylene blue (BM), Reactive Orange 16 (RO16) and Methyl Orange (MO) from water by adsorption. The activated carbons were prepared by chemical activation using phosphoric acid as activation agent. Chemical characteristics of these activated carbons was monitored by Bohem titration and the method of Lopez-Ramon et al. while surface areas of the samples were determined by nitrogen adsorption/desorption isotherm measurement. Activated carbons CA-K and CA-C have the following characteristics: BET surface and the pore volumes are respectively 1148 m2/g and 0.607 cm3/g for CA-K, 584 m2/g and 0.298 cm3/g for CA-C. The two activated carbons synthesized are microporous activated carbon with micropores volume representing more than 70% of the total pore volume. The removal of dyes was studied using batch reactor. The nature of the activated carbon and the dyes are the key factors influencing the contact time. At the equilibrium times (35 to 270 min for CA-K and 60 to 300 min for CA-C), the removal of BM, MO and RO16 was quasi-total while for RB5 the amount adsorbed was about 83%. Based on the adsorption capacity, it was shown that CA-K was more effective than CA-C. Various kinetic models such as pseudo first-order, pseudo second-order and intraparticle diffusion were used to evaluate the mechanism of dyes adsorption on activated carbons. BM, RO16, and MO removal process was found to be governed by second-order kinetic while pseudo-first order kinetic is suitable for RB5 adsorption study. The pHs of the solutions and the amount of activated carbon have strong effect on the adsorption capacity of these dyes. An acid pH (for anionic dyes) and basic pH (for cationic dyes) were favorable for the maximum adsorption of dyes. The isotherm data could be well described by the Freundlich and Langmuir equations in the concentration range of 0–80 mg/L. For the present adsorption process intraparticle diffusion of dyes within the particle was identified to be rate limiting. Both activated carbons were shown to be promising materials for adsorption removal of dyes from aqueous solutions.