Kinetics and equilibrium studies of methylene blue adsorption by spent coffee grounds

Spent coffee grounds (SCG), a residue from the soluble coffee industry. was evaluated as an adsorbent for the removal of methylene blue (MB) from aqueous solution. Batch adsorption tests were performed at 25 degrees C and the effects of contact time, adsorbent dosage, and pH were investigated. Adsorption kinetics was determined by fitting first and second-order kinetic models to the experimental data, with the second-order model providing the best description of MB adsorption onto spent coffee grounds. The typical dependence of dye uptake on kinetic studies indicated the adsorption process to be both chemisorption and diffusion controlled. The experimental adsorption equilibrium data were fitted to Langmuir, Freundlich and Tempkin adsorption models. The experimental data obtained in the present study indicate that spent coffee grounds are suitable candidates for use as adsorbents in the removal of cationic dyes. (C) 2009 Elsevier B.V. All rights reserved.