Transport mechanism of Malachite Green (MG) to adsorb on used black tea leaves (UBTL) was studied by applying different transport model equations to the kinetic data of adsorption. The effects of particle size of adsorbent and the initial dye concentration on the rate of adsorption were studied in batch process at constant solution pH and temperature to distinguish the reaction-controlled and transport controlled. A significant effect of particle size of the UBTL on the adsorption rate indicated that the adsorption of MG by UBTL follows transport controlled mechanism. Again, the decreasing of the extent of adsorption with an increase in particle size supports the involvement of diffusion phenomena in this transport mechanism. Verification of parabolic diffusion model and film diffusion model suggested that the film resistance is insignificant to the transfer of MG to UBTL but it seems to be diffusion controlled with an increase in initial MG concentration in the solution. The intraparticle diffusion is the rate-determining step in the uptake of MG by the UBTL and small particle size of UBTL is more favorable for intraparticle diffusion controlled mechanism.
