Kinetics and Thermodynamics of Cadmium(II) and Zinc(II) Adsorption onto Oil shale fly ash

The kinetics and thermodynamics characteristics of Cd(II) and Zn(II) adsorption onto fly ash of a oil shale-fired power plant was investigated by using batch adsorption method. The results showed that Langmuir and Freundlich adsorption isotherms were applicable to the adsorption process, while Freundlich equation is more applicable. The mechanistic steps of the adsorption process was studied through data fitting of the experimental data using the equation of Lagergren pseudo-first-order kinetics, the pseudo-second-order kinetics, and the intraparticle diffusion model. All the three equations were found applicable in initial stage of this study, and the absorptions of Cd(II) and Zn(II) onto fly ash from oil shale-fired CFB was in accordance of the pseudo-2nd-order reaction kinetics. The absorption characteristics of metal ions on oil shale fly ash were controlled by both film diffusion and particle diffusion. Thermodynamic analysis showed that the processes of oil shale fly ash adsorption Cd(II) and Zn(II) are endothermic reaction, and it is a spontaneous process at higher temperature.