Kinetics of adsorption of methylene blue onto activated carbon prepared from palm kernel shell

The kinetics of adsorption of methylene blue from aqueous solution onto activated carbon prepared from palm kernel shell has been investigated. The time dependent studies showed a rapid adsorption in the first ten minute. A batch sorption model based on the assumption of the pseudo first and second order mechanism, were applied to predict the rate constants. The adsorption process follows the pseudo-second order kinetic, having a correlation coefficient in the range between 0.98 and 1. The pseudo second order rate constant k2 was found to generally decrease from 1.79 to 4.5 x 10-2 as the initial concentration increased from 5 to 25 ppm but increased from 4.9 x 10-2 to 2.3 x 10-1 with increased temperature, suggesting that the adsorption process is endothermic. Intra-particle diffusion was confirmed as one of the rate determining steps; as such the adsorption mechanism is controlled by particle diffusion rather than film diffusion.