Equilibrium and kinetics studies of adsorption phosphate on raw and novel lithium silica fume based adsorbent

Abstract

In this study, the adsorption of phosphate from aqueous solution by lithium silica fume (LSF) with or without iron oxides modification was investigated. Iron oxides modification was achieved by in situ generation of iron oxides on LSF by applying three different kinds of ferric solution (FeCl₃·6H₂O, Fe(NO₃)₃·9H₂O, and Fe₂(SO₄)₃) with Na₂CO₃ addition. Batch adsorption studies were carried out for better understanding of their adsorption behaviors towards phosphate. Among three iron oxide modified adsorbents, FeCl₃-modified LSF (FeCl₃/LSF) exhibited highest S_BET, and best adsorptive capability towards phosphate. The adsorption kinetics data of phosphate adsorption onto FeCl₃/LSF fitted well with Langmuir model and Freundlich model. The maximum phosphate adsorption capacity onto FeCl₃/LSF is 13.39 mg g⁻¹ at 25°C, almost three times higher than that of LSF. The X-ray diffraction pattern showed new species of Fe(PO₃)₃ that was formed on FeCl₃/LSF after adsorbing onto phosphate, which indicated chemisorption was involved in phosphate adsorption; this phenomenon is in accordance with SEM-EDS, FTIR, and X-ray photoelectron spectroscopy analysis. The coexistence of Cl⁻, , slightly affected phosphate removal, while coexistence of greatly reduced the adsorption of phosphate. The relatively low cost and high capabilities of FeCl₃/LSF make it a potentially attractive adsorbent for removing phosphate from aqueous solution.

Keywords:

• Iron oxide modified lithium silica fume
• Phosphate removal
• Adsorption behavior
• Isotherms
• Kinetics

Acknowledgments

The authors are grateful for the help from Project 2015SCU11028.