The results show that the pseudo-second-order mechanism is predominant and that chemisorption might be the rate-limiting step that controls the adsorption process.
However, when the diffusion process (intra-particle or transport-pore diffusion) mainly controls the adsorption process, the sorption capacity will increase with the increase in temperature.
The pH of system controls the adsorption capacity due to its influence on the surface properties of the adsorbent as well as ionic forms of the chromium solutions.
Results were employed to explain the kinetic mechanism that controls the adsorption process by means of the pseudo-first-order, pseudo-second-order, Elovich, and intraparticle diffusion models.
Evaluation of adsorption site energy distributions (generated using the model coefficients) suggested that the negatively charged ceria surface had a very broad site energy distribution and that its surface heterogeneity controls the adsorption process.
As pH of the system controls the adsorption capacity through its influence on the surface properties of the adsorbent and species of adsorbate in solution, the effect of pH on adsorption of fluoride was studied in the pH range of 2.0 10.0 and results are depicted in Fig. 4a, b.
