Phosphate adsorption from aqueous solution by lanthanum–iron hydroxide loaded with expanded graphite

ABSTRACT

In this study, a novel adsorbent of expanded graphite loaded with lanthanum (III)–iron (III) hydroxide (EG-LaFe) was prepared for phosphate removal. The single factor of oscillating time, La/Fe molar ratio and total concentration of EG-LaFe were studied for optimization of preparation conditions. Effects of contact time, initial phosphate concentration, adsorption temperature and coexisting ions on the phosphate removal performance of EG-LaFe were investigated in detail. Adsorption kinetics and isothermal adsorption studies showed that the pseudo-second-order and the Langmuir model fitted the experimental data quite well. Thermodynamic analysis showed that the phosphate adsorption of EG-LaFe was spontaneous and endothermic. In addition, EG-LaFe exhibit high sorption selectivity toward phosphate over other coexisting ions. The phosphate adsorption mechanism was investigated by means of pH study, scanning electron microscopy and Fourier transform infrared spectroscopy. The results demonstrated that the probable mechanisms of phosphate adsorption on EG-LaFe were the replacement of surface hydroxyl groups (M-OH), electrostatic interaction and Lewis acid–base interaction.

KEYWORDS:

• Phosphate removal
• adsorption
• lanthanum–iron bimetal composite
• expanded graphite
• mechanism

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by National Key Technology Research and Development Program of the Ministry of Science and Technology of China [grant number 2014BAB11B00]; Program for Innovative Research Team in University of Shanghai Municipal Education Commission [grant number IRT13078] and National Natural Science Foundation of China [grant number 21207085].