Phosphate removal using aluminum–doped rice husk ash–derived silica

Abstract

Phosphate, a compound which has phosphorus as its key atom, from excess fertilizers and detergents ends up washing into lakes, creeks and rivers. This overabundance of phosphorus causes excessive aquatic plant and algae growth and depletes the dissolved oxygen supply in the water. In this study, aluminum–doped mesoporous adsorbents were tested for their ability to remove phosphate from water. Aluminum–doped rice husk ash–derived silica (Al–RHA) was synthesized by cogellation method and applied as adsorbent for removal of phosphate in laboratory batch adsorption studies. The synthesized Al– RHA was characterized by nitrogen adsorption– desorption, Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). Al–RHA exhibited fast adsorption kinetics as well as high adsorption capacities. The optimum phosphate removal was determined in initial concentration of 0.3 mg PO43–/L with 0.3 g of adsorbent dosage at acidic condition after 3 h. Freundlich isotherm was concluded to be the preferred model for the adsorption process. The regenerated Al–RHA was found to have 76% phosphate removal capacity after being recycled once. The amount of adsorbent and initial concentration of phosphate solution had little effect on the concentration of residual aluminum ions, whereas the concentration of residual aluminum ions decreases with the increase in pH of the solution.