Studying the kinetics and mechanism of tartrazine removal by activated carbon under the influence of shaking speed using Diffusion-Binding model

Abstract

The kinetic and mechanistic study of the removal rate of tartarzine by adsorption onto activated carbon under the influence of shaking speed is presented in this work. Diffusion binding model (DB-model) and pseudo second order model (PSO-model) were applied for suggesting the dependency of surface-reaction (solute or active site) and to give the main outputs; adsorption rate constants and capacities. According to error evaluation of both models, it was found that DB-model is more representative for tartarzine activated carbon adsorption system than PSO-model and it is suggested that surface-reaction kinetic is dependent on tartrazine concentration not on active sites of adsorbent. In addition, DB-model showed that adsorption rate constants and capacities increase with shaking speed which agrees with the fact of enhancing some diffusion steps because of shaking. DB-model, as a diffusion model as well, was applied to investigate diffusion mechanistic and it was concluded that for static condition (shaking speed = 0 rpm), adsorption passes two stages, the first is controlled by bulk-diffusion and film-diffusion and the second is controlled by intraparticle-diffusion. For shaking speeds 25 rpm and 50 rpm, bulk-diffusion and filmdiffusion almost have no contribution in controlling overall rate and consequently intraparticle-diffusion is the controlling step. For shaking speeds from 75 to 125 rpm, intraparticle-diffusion is suggested to have strong contribution in controlling adsorption process.