Highly efficient removal of phosphate using a novel Fe-La binary (hydro)oxide as adsorbent: behavior and mechanism

Abstract

Phosphate has been proved to be one of the main elements causing eutrophication of water bodies. However, the elevated phosphate concentrations in the water bodies are often due to the excess discharge of wastewater containing phosphate. Therefore, treatment of elevated phosphate-containing wastewater is of vital importance to alleviate the situation. In this study, a novel Fe-La binary (hydro) oxide adsorbent was synthesized via a facile coprecipitation method for effective phosphate removal from wastewater. The adsorbent grains were formed of primary nanoparticles. Batch experiments were carried out to investigate adsorption kinetics and equilibrium. The adsorption was fast and well fitted by the pseudo-second-order equation, indicating that the adsorption process might be chemical sorption. The adsorption isotherms could be well described by Freundlich model and the maximal adsorption capacity reached 80.7 mg/g at pH 6.0 +/- 0.1 and 67.4 mg/g at pH 9.0 +/- 0.1, respectively, much higher than many reported adsorbents. The phosphate adsorption was pH dependent and weakly acidic condition was favorable for the adsorption. The phosphatead sorption might be mainly achieved via the replacement of surface hydroxyl groups at the solid surface and the formation of inner-sphere surface complexes. Moreover, the spent adsorbent could be effectively regenerated using dilute NaOH solution and used repeatedly. All these results suggest that the adsorbent maybe a promising alternative for phosphate removal.