Performance and Mechanisms of Fluoride Removal from Groundwater by Lanthanum-aluminum-loaded Hydrothermal Palygorskite Composite

Lanthanum-aluminum loaded hydrothermal palygorskite(La-Al-HP) composite was prepared and selected as adsorbent for the fluoride removal from simulated groundwater. The adsorbent was characterized by scanning electron microscopy(SEM), Brunauer-Emmet-Teller(BET) analysis, X-ray diffraction(XRD) analysis and X-ray photoelectron spectroscopy(XPS). SEM visualization shows that the dense surface structure of raw HP appeared loose and presented micro canals after modification. The BET analysis also proved the specific surface area of La-Al-HP composite(95.58 m²/g) was higher than that of the raw HP(34.31 m²/g). Subsequently, the adsorption capacity of La-Al-HP composite was demonstrated in adsorption experiments. The kinetics of fluoride ion adsorption into La-Al-HP composite followed the pseudo-second order with a correlation coefficient of 0.997. The isotherm data was well fitted with the Langmuir model. The monolayer adsorption capacity of La-Al-HP composite was 1.30 mg/g. The XRD and XPS results reveal that the La³⁺ and Al³⁺ ions were loaded on the surface of modified HP and the fluoride ion was adsorbed onto the La-Al-HP composite. A large amount of La-Al-O composite oxide existing on the surface of La-Al-HP composite might be the immanent cause for the excellent adsorption capacity of fluoride ions.