Synthesis of a Matériaux Institut Lavoisier metal-organic framework 96 (MIL-96(RM)) using red mud and its application to defluorination of water

High concentration of fluoride is detrimental to both the water environment and human health. In this work, a Matériaux Institut Lavoisier metal-organic framework 96 (MIL-96(RM)) was hydrothermally synthesized using metal ions present in red mud (RM) for fluoride removal from water. Various of processes were used to characterize the prepared adsorbent, and its adsorption behavior was extensively studied to determine its fluoride removal efficacy. The removal rate of fluoride improved with increasing adsorbent dosage, whereas temperature and the presence of coexisting anions had little effect on the performance of fluoride removal. A pseudo-second-order kinetics model was a good fit with the measured adsorption kinetics, and the results of adsorption thermodynamics revealed that the adsorption process was endothermic and spontaneous. Taken together, these findings indicated that the likely mechanism for fluoride adsorption was ion exchange, with a maximum adsorption capacity of 82.645 mg g–1 at 293 K being observed. Notably, the fluoride removal rate of MIL-96(RM) still exceeded 50 % after seven regeneration cycles with 1.5 M NaOH solution. This study established that the new MIL-96(RM) adsorbent effectively removed fluoride from water, thereby providing a new opportunity for RM reuse and a strategy to reduce pollution caused by the metal ions present in RM.