Design and optimization of an innovative lanthanum/chitosan bead for efficient phosphate removal and study of process performance and mechanisms

Abstract

Presence of excessive phosphorus in surface waters is the main cause for eutrophication. In this study, a lanthanum/chitosan (La/CS) bead was prepared so as to provide a cost-effective solution to the problem. The optimization of bead for the treatment was conducted, leading to the optimal condition: 30 wt% La/CS bead at a dosage of 30 g L−1 (wet weight). A higher phosphate removal around 90% was obtained in pH 4.0–10.0. Most of uptake occurred in the first 2 h and the equilibrium was reached in about 6 h. Coexisting ions of Cl−, NO3−, HCO3−, and SO42− had negligible effects on the treatment, while the presence of F− reduced the uptake by 10.39%. The maximum adsorption capacity of 261.1 mg-PO4·g−1 (dried weight) at pH 5.0 was achieved, which is much better than many reported La-based adsorbents. The adsorbed phosphate can be effectively recovered with an alkaline solution. A multi-cycle regeneration-reuse study illustrated that the treated water still met the phosphorus discharge standard. The characterization results demonstrated the disappearance of La(OH)3 and La2(CO3)3 on the bead and the formation of NH3+ … P and La–P groups after the adsorption, indicating the significant roles of ion exchange and electrostatic attraction on the uptake. The excellent performance found in this study clearly indicates that the optimized La/CS bead is promising in the treatment of phosphate and perhaps its recovery for industrial use.