Expanded graphite loaded with lanthanum oxide used as a novel adsorbent for phosphate removal from water: performance and mechanism study

Abstract

A novel adsorbent of expanded graphite (EG) loaded with lanthanum oxide (EG-LaO) was prepared for phosphate removal from water and characterized by scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR) spectroscopy. The effects of impregnation time, La³⁺ concentration, activation time, and activation temperature on the phosphate removal performance of the adsorbent were studied for optimization of preparation conditions. Isothermal adsorption studies suggested that the Langmuir model fits the experimental data well. Adsorption kinetics investigation showed that the pseudo-second-order model fits the experimental data quite well, indicating that the adsorption process is mainly a process of chemical adsorption, and chloride ions compete to react with the active sites of the adsorbent but do not prevent phosphate from adsorbing onto EG-LaO. The adsorption mechanism studies were performed by a pH dependence study of the adsorption amount. The results demonstrated that the probable mechanisms of phosphate adsorption on EG-LaO were electrostatic and Lewis acid–base interactions in addition to ion exchange.

Keywords:

• phosphate removal
• adsorption
• expanded graphite (EG)
• lanthanum oxide (LaO)
• interfering ions

Acknowledgements

The work was supported by National Natural Science Foundation of China under Grant (No. 21207085); Innovation Program of Shanghai Municipal Education Commission under Grant (No. 14YZ014); and Program for Innovative Research Team in University of Shanghai Municipal Education Commission under Grant (No. IRT13078).