Adsorption behavior of phosphate on Mg–Al layered double hydroxide/montmorillonite composite

Abstract

In this study, Mg–Al-layered double hydroxide (LDH) and montmorillonite (M) were mixed (mass ratio = 1:1) with high-shear action to prepare a mineral composite (LDH–M). The structure, morphology, and textural properties of LDH and LDH–M were investigated via X-ray diffraction, field-emission scanning electron microscopy, Fourier transform infrared spectroscopy, and nitrogen physisorption. The phosphate adsorption performances of LDH and LDH–M were assessed and compared by conducting batch experiments. The effects of initial adsorbate concentration and contact time on phosphate uptake were examined. The adsorption kinetics and isothermal adsorption of both adsorbents showed that the pseudo-second-order model and the Langmuir isotherm fitted well with the experimental data. The maximum adsorption capacity of 127.8 mg g⁻¹ of phosphate onto LDH–M improved by ~21% compared with that onto pure LDH. Hence, the composite exhibited better affinity toward phosphate adsorption than pure LDH. The enhanced adsorption of phosphate by LDH–M probably resulted from the textural changes of the composite compared with those of its precursors. The adsorption process mainly follows ion-exchange mechanism. The results revealed a synergic effect between LDH and M during phosphate removal.

Keywords:

• Layered double hydroxides
• Montmorillonite
• Composite
• Phosphate
• Sorption

Acknowledgments

The authors acknowledge the financial support of the Science Foundation of Shandong Province, China (2008E24).