Affecting factors, equilibrium, kinetics and thermodynamics of bromide removal from aqueous solutions by MIEX resin

Abstract

It is necessary to remove bromide from raw water owing to the fact that bromide directly leads to the brominated disinfection byproducts during the disinfection process for drinking water. The adsorption characteristics of bromide by MIEX resin are investigated in a batch mode. Some factors such as initial bromide concentration, contact time, adsorbent dosage, pH of solution and coexistent anions, have significant effect on bromide removal. Five isotherm models, namely, Langmuir, Freundlich, Temkin, Dubinin–Radushkevich and Redlich–Peterson, are used to fit the equilibrium data of bromide on MIEX resin at 303K. The results show that the adsorption equilibrium can be well fitted by the Freundlich and Redlich–Peterson isotherm models. The pseudo first-order and second-order kinetics models are used to fit the kinetics process of bromide adsorption on MIEX resin. The results demonstrate the adsorption kinetics agree with the pseudo second-order model, indicating the adsorption of bromide on MIEX is chemical sorption. The intra-particle diffusion model is used to further analyze the diffusion mechanism of bromide during the adsorption process. The results imply that the intra-particle diffusion is not the only rate limiting step. The negative ΔG° values indicate that the adsorption of bromide on MIEX resin is thermodynamically feasible and is a spontaneous process. The negative ΔH° and ΔS° show that the adsorption is an exothermic process in nature and the randomness degree at the solid/liquid interface decreases after adsorption.