La(III)-bentonite/chitosan composite: A new type adsorbent for rapid removal of phosphate from water bodies

It is highly imperative to remove phosphorus from water bodies because the excessive phosphorus content can cause eutrophication of water bodies. In this work, we prepare a kind of environmentally friendly and low-cost adsorbent comprising lanthanum (La)-doped bentonite and chitosan, with a simple, facile and scalable method combining direct calcination and subsequent blending. The optimal adsorbent, La-doped bentonite/chitosan-5, La-BC-5 hereinafter, can rapidly reach equilibrium in 20 min and provide 93.2% adsorption efficiency (initial phosphate concentration, 50 mg/L); and as high as 99.7% could be removed in 5 min under low phosphate concentration (2 mg/L). Fitting result indicates the phosphate adsorption isotherm fits the Freundlich model, meanwhile the adsorptive kinetics follows a pseudo-second-order model. Anti-interference result for some typical anionic species including NO3-, SO42-, Cl-, indicates 97.5% removal efficiency could be achieved under coexisting phosphate concentration of 5 mg/L. Meanwhile, reusability experiment reveals that removal efficiency decreases to 89.1% after five regeneration cycles. Notably, practical water adsorption experiment manifests the La-BC-5 can efficiently reduce the phosphate concentration from 0.30 to 0.07 mg/L. The favorable properties with rapid adsorption, excellent anti-interference for coexisting anions and reusability foresee the enormous potentials for practical phosphate removal in water bodies.