Kinetics and thermodynamics of zinc removal from a metal-plating wastewater by adsorption onto an Iranian sepiolite

The study of the kinetics and thermodynamics of the adsorption process can provide valuable information for the proper design and control of adsorption systems. The influence of temperature on the kinetics of Zn2+ sorption on an Iranian sepiolite sample was investigated through a series of batch experiments. Consistent with an exothermic reaction, an increase in the temperature resulted in decreasing Zn2+ adsorption rate. The sorption kinetics was tested for pseudo-first-order, pseudo-second-order, and intraparticle diffusion models, and the rate constants were calculated. Results showed that the adsorption kinetics followed the pseudo-second-order kinetic model. The intraparticle diffusion model described that sorption of Zn onto the sepiolite particles is a two-step process, and intraparticle diffusion is not the only rate-limiting step. The results obtained from the study of thermodynamic data indicated that sorption of Zn onto sepiolite is non-spontaneous and less favored at higher temperatures.