Lanthanum modified chitosan-attapulgite composite for phosphate removal from water: Performance, mechanisms and applicability.

A novel lanthanum-modified-chitosan-attapulgite (La-CTS-ATP) composite with efficient adsorption of phosphate in water was prepared and characterized. The adsorption properties were investigated by adsorption kinetics, adsorption isotherms and thermodynamics. An orthogonal design test was used to explore the optimal preparation conditions of La-CTS-ATP. Various characterizations exhibited the successful modification of lanthanum and the effective adsorption of phosphate. The batch experiments showed that La-CTS-ATP exhibited excellent stability within pH range of 4-10 and the disturbance of co-existing substances (Cl-, NO3-, HCO3-, SO42-). Chemisorption played the main role in phosphate adsorption from kinetic studies. Isotherm studies illustrated monolayer uptake of adsorbents onto the adsorbent, and the maximum adsorption capacity was 102.90 mg/g, much higher than other La-based adsorbents. The reaction process was spontaneous (ΔG < 0), exothermic (ΔH < 0) and disordered (ΔS > 0) from thermodynamic analysis. The excellent reusability of La-CTS-ATP was investigated, after five cycles, the phosphate removal rate and desorption rates were 72.93 % and 77.44 %, respectively. The dynamic adsorption experiments showed that the faster the flow rate, the shorter the time for La-CTS-ATP to get saturation, and the maximum adsorption capacity was slightly reduced. The surface precipitation, electrostatic attraction, and ligand exchange were the main mechanisms affecting its adsorption behavior. The adsorbent exhibited excellent effectiveness in real wastewater (breeding wastewater and domestic wastewater). In this study, a novel and effective adsorbent for phosphorus removal was produced in contaminated water, and the analysis of the adsorption process of the system provides new insights for related research.