Efficient fluoride removal from aqueous solution by synthetic FeMgLa tri-metal nanocomposite and the analysis of its adsorption mechanism

Highlights: • No calcination was needed in the preparation. • The role of individual metal in the nanocomposite was illustrated. • The nanocomposite has high defluoridation performance. • The adsorption mechanism was revealed. La is highly electrically affinitive for fluoride ions, but it is costly. Therefore, it is reasonable to mix it with cheap metals to form hybrid materials. On the other hand, calciniation process is usually needed in preparation of many adsorbents based on metal elements, which is energy and time consuming and not environment-friendly. In the present study, a novel FeMgLa tri-metal nanocomposite was facilely prepared by co-precipitation without calcination. The role of individual metal in the tri-metal nanocomposite was illustrated. The samples were characterized by BET, SEM, TEM, Mapping EDS and XPS. Various influencing factors such as coexisting anions, pH and contacting time were studied in detail. Sorption isotherms showed that the sorption capacity of fluoride is 13.2 mg/g at the equilibrium fluoride concentration of 1 mg/L, and the maximum sorption capacity is 47.2 mg/g, indicating the high defluoridation performance of the adsorbent. The F⁻ saturated adsorbent can be regenerated by alkaline and reused. Adsorption mechanism was analysized in detail, and the results indicated that F ions were able to substitute for all three metal-OH groups, and strong interactions happened between fluorion and the metals in the adsorption. The adsorption mechanism was speculated to be ligand exchange, which could be well supported by experimental results. The adsorbent is promising to treat fluoride polluted waters due to its high adsorption efficiency, low cost and easy operation.