The influence of stirring upon the adsorption of a cationic surfactant onto activated carbon particles

The adsorption rate of the cationic surfactant cetyl trimethylammonium bromide (CTAB) onto particles of activated carbon has been determined from measurements of the changes in the conductivity of the supernatant solution. This technique exhibited a high sampling frequency which enabled detailed analysis of the adsorption kinetics. It was demonstrated that the adsorption rate was generally positively correlated with the stirring rate, although the effect was small. The adsorption rate could be modelled by 1.3-order kinetic equations; first-order kinetic treatment only approximately described the process, but gave a better description than second-order kinetics. The hypothesis that adsorption was controlled by the intra-particle diffusion mechanism was not supported by the data. In addition, the technique enabled the construction of adsorption isotherms of ionic surfactants onto particles. In this case, the adsorption equilibrium was described by a Langmuir isotherm.