Kinetics and thermodynamics of adsorption of heavy metal ions onto fly ash from oil shale

The kinetics and thermodynamics characteristics of Pb²⁺, Cu²⁺, Zn²⁺, Cd²⁺ adsorption onto fly ash from an oil shale-fired power plant was investigated using batch adsorption method. The results show that Freundlich equation is more applicable than Langmuir equation. The adsorption process was studied through fitting of the experimental data using the equation of Lagergren pseudo-first-order kinetics, the pseudo-second-order kinetics, the Elovich equation, and the intraparticle diffusion model. All the four equations were found applicable in initial stage of the adsorption. The absorption of Pb^2+, Cu²⁺, Zn²⁺, Cd²⁺ on fly ash from oil shale-fired CFB was in accordance of the pseudo-2nd-order reaction kinetics in the entire stage. The absorption characteristics of metal ions on oil shale fly ash is controlled by both film diffusion and particle diffusion. Thermodynamic analysis show that the processes of oil shale fly ash adsorbing Pb²⁺, Cu²⁺, Zn²⁺, Cd²⁺ are endothermic reaction.