Removal of phosphate anions using the modified chitosan beads: Adsorption kinetic, isotherm and mechanism studies

• Chitosan beads modified with zirconium (ZCB) were prepared and used for P sorption.
• Various models and isotherms were employed to describe the adsorption process.
• Isoelectric points of ZCB and ZCB-P kept the same charge at pH of 3.5.
• Mechanism for P adsorption was electrostatic attraction and ion exchange reaction.

A new chitosan biosorbent modified with zirconium ions (ZCB) was prepared and employed for the adsorption of phosphate ions from aqueous solution. Batch of experiments were performed to investigate the effects of various conditions on the phosphate adsorption, including contact time, the initial concentration of phosphate ions, temperature and pH. The experimental data were interpreted elaborately by the different models of adsorption kinetics and isotherms. The results showed that the kinetic data were well fitted to the pseudo first-order and second-order models, indicating that the adsorption behaviors were mainly ascribed to both physic-sorption and chemic-sorption. The further analysis of kinetics indicated that the intra-particle diffusion was the rate controlling process. The equilibrium data were best described by the Langmuir isotherm model with maximum monolayer adsorption capacity of 60.6 mg g− 1. The values of △ G°, △ S° and △ H° revealed that the nature of adsorption was feasible, spontaneous and endothermic. FTIR, EDS, XPS and zeta potential studies suggested that the adsorption mechanism was possibly attributed to the electrostatic attraction and ion exchange reaction between ZCB and phosphate ions.

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