Heating induced hierarchically mesoporous adsorbent derived from natural hydromagnesite for highly efficient defluoridation of water

Abstract Hierarchically mesoporous adsorbent derived from natural hydromagnesite with remarkable adsorption capacity for fluoride (F−) has been synthesized through the facile one-step calcination. Various characterizations confirmed that calcination temperature was directly correlated with their crystallite structures, surface properties, and adsorb ability. The hydromagnesite calcined at 500 °C (CH-5) exhibits the highest adsorption capacity and rate towards F−. The F− adsorption isotherm data was explored by both Langmuir and Freundlich model and the maximum adsorption capacity of CH-5 was 69.6 mg/g. Kinetic study revealed that the adsorption kinetics follows the pseudo-second-order model, suggesting the chemisorption mechanism. Regeneration study showed that the adsorption ability for fluorine can be completely recovered by calcining at 500 °C, and after five cycles, the adsorption ability is not significantly weakened. After detailed evaluation, the enhancement mechanism of the calcined product can be attributed to relatively higher specific surface area and exposed more magnesite active sites due to the maintenance of the intrinsic three-dimensional layer structure during the dehydration and decarbonation, which were responsible for the striking adsorption abilities. The green adsorbent originated from natural mineral with the characteristics of low cost, high adsorption ability and recoverability is advantageous for fluoride-containing wastewater treatment.