Magnetically separable and recyclable lanthanum/iron co-modified attapulgite: A sustainable option to efficiently control phosphate loading

Challenges remain in developing sustainable (high-efficient and recyclable) phosphate removal systems with lower costs and reduced secondary pollution when lanthanum (La)-based sorbents are applied to control phosphate in the aquatic environment. To address this issue, a phosphate stabilizing compound, namely magnetic lanthanum/iron co-modified attapulgite (M-LaFeAP), was fabricated by incorporating lanthanum into an iron-modified attapulgite (M-FeAP). Batch experiments demonstrated that 88.34% of the phosphate was rapidly sequestered from aqueous solution within the first hour, and the composites reached a maximal sorption capacity of 43.32 mg/g. The pseudo-second-order model was found to better explain the M-LaFeAP adsorption kinetics and the equilibrium data fitted very well with the Langmuir isotherm model. With the initial phosphate concentration ranging from 2 to 100 mg/L, the M-LaFeAP exhibited superior adsorption performance from 2 to 10 of pH values. In addition, M-LaFeAP presented an excellent selectivity for phosphate when co-existing ions often occurring in water bodies were present, in which the solution ionic strength exerted little influence on phosphate sorption behavior. Notably, the recyclable M-LaFeAP possessed a saturated magnetization of 25.83 emu/g and was easily separated under the external magnetic field. After five serial adsorption-desorption cycles, M-LaFeAP still possessed a better sorption performance (35.78 mg/g), which demonstrated its appreciable reusability for phosphate removal. Our findings indicate that the separable and recyclable M-LaFeAP demonstrated high-efficient phosphate removal in a sustainable way, which is promising in phosphate removing and recovering applications.