Removal of fluoride using magnesium and iron complex hydroxides

Abstract

© IWA Publishing 2020 In this study, metal complex hydroxide materials containing magnesium to iron in molar ratios of 3:1 and 5:1, referred to in this study as Mg-Fe-CH3.0 and Mg-Fe-CH5.0, respectively, were prepared, and their adsorption capability with respect to fluoride ions was investigated. The physicochemical characteristics of adsorbents were determined using scanning electron microscopy and X-ray diffraction, and specific surface area and the number of hydroxyl groups were calculated. The adsorption behaviors and mechanism of fluoride ions were assessed. The adsorption capability of fluoride ions using Mg-Fe-CH3.0 was greater than that using Mg-Fe-CH5.0. In addition, the amount adsorbed depended on the adsorption temperatures; the adsorption was comparatively less at 5 °C than at 25 °C. Adsorption mechanism of fluoride ions was evaluated by elemental distribution analysis and binding energy. The binding energy of fluorine onto Mg-Fe-CH3.0 and Mg-Fe-CH5.0 could be detected after adsorption. Additionally, it was clear that one of the adsorption mechanisms was related to the ion exchange between fluoride ions and chloride ions in the interlayer space of the Mg-Fe-CH3.0 and Mg-Fe-CH5.0 (correlation coefficient 0.923–0.965). This study illustrates that both Mg-Fe-CH3.0 and Mg-Fe-CH5.0 have a high potential for fluoride ion adsorption from the aqueous phase.