Adsorption of fluoride at the interface of water with calcined magnesium–ferri–lanthanum hydrotalcite-like compound

Abstract

In this work, a new adsorbent, Mg/Fe/La hydrotalcite-like compound (defined as Mg/Fe/La HLc), was synthesized with a facile one-step hydrothermal method for removing fluoride from water. Several measurements, such as XRD, FT-IR, SEM, XPS and N₂ adsorption–desorption technique, were used to characterize the adsorbent and to approach into the adsorption of fluoride at the interface of water with calcined Mg/Fe/La hydrotalcite-like compound (defined as Mg/Fe/La CHLc). The experimental results have shown that the adsorption was well described by the pseudo-second-order model and followed Langmuir isotherm. The maximum adsorption capacity reached 60 mg g⁻¹, and the desorption could be easily realized in a aqueous Na₂CO₃ solution, indicating that the Mg/Fe/La CHLc could be used as a potential adsorbent for effectively removing fluoride from water. The mechanisms of the adsorption might be attributed to the chemisorption due to the complexation of fluoride in water with lanthanum on the surfaces of the Mg/Fe/La CHLc, besides of the surface adsorption and interlayer adsorption due to the “memory effect” of hydrotalcite. In addition, it was found that the element of lanthanum in the adsorbent played a great role in the adsorption of fluoride in water.