Fluoride removal from liquid phase by Fe-Al-La trimetal hydroxides adsorbent prepared by iron and aluminum leaching from red mud

Fe-Al-La trimetal hydroxides adsorbent was synthesized by utilizing iron and aluminum as the main raw material, which were leached from red mud, for the removal of fluoride from aqueous solution. The as-prepared samples were characterized by XRD, BET, SEM, FT-IR, and XPS techniques. The results demonstrated the amorphous structure with a high surface area of 371.47 m2/g was obtained by the sample. The optimized adsorption parameters were 10 mg/L concentration, 6.8 ± 0.2 pH, 0.1 g/L dose, 240 min contact time and 25 °C temperature. Adsorption data fitted well with the Langmuir isotherm and pseudo-second-order kinetic model. The Fe-Al-La adsorbent exhibited high fluoride removal efficiency in a wide pH range from 3 to 9, and the maximum adsorption capacity of 74.07 mg/g. All metals involved in the removal of fluoride from aqueous solution were trivalent. The adsorption mechanisms for fluoride were electrostatic interaction and ion-exchange.