Search

[Display omitted] • Fluoride (FL) is abundant in the earth's environment and is often discharged into aquifers. • Fluorosis is the outcome of continuous exposure to FL concentrations of more than 4 ppm. • CM for FLR have a long lifespan and are highly resistant to harsh conditions. • EDI for FLR shows a reduction in labor costs and no chemicals required for resin regeneration. • MCDI offers significant potential for the removal of organic pollutants including fluoride. One of the biggest issues facing the globe today is fluoride poisoning of water, which is a severe risk to the well-being of people since water is essential for consumption from both natural and man-made sources. Fluoride in water can be removed using a variety of methods, although the issue is still not completely solved. Because of its ionic size and reactivity, fluoride can be hard to remove from water-based solutions using traditional electrochemical, precipitation, and adsorption methods. One of the latest innovations that has been shown to be highly successful in bringing fluoride levels down to the required levels is the use of membranes. This review discusses fluoride and its characteristics, sources, impacts on the environment and humans, fluoride measurement techniques, and fluoride applications. The efficacy of different types of membrane separation processes are covered with respect to techniques developed, advantages and drawbacks of defluoridation processes. This review critically examines membrane-based techniques for different defluoridation processes including nanofiltration (NF), reverse osmosis (RO), membrane distillation (MD), electrodialysis (ED), and forward osmosis (FO). Furthermore, the study addresses developments in ceramic membranes, electrodeionization and membrane capacitive deionization, hybrid membrane techniques, and life cycle assessment (LCA) for membrane-based defluoridation process. The work meets the SDGs goal #6 of clean water supply. [ABSTRACT FROM AUTHOR]

[Display omitted] • A CNT-CeO 2 electrode is fabricated to selectively remove F− in mixed ion solutions. • CNTs increase the conductivity of the electrode and hinder the aggregation of CeO 2. • Pseudo-capacitance behavior of F– entering CeO 2 was observed first time by EQCM. • The energy consumption for treating actual groundwater using scaled-up equipment is low at approximately 0.2 kWh/m3. Selective capacitive deionization (SCDI) is a promising process for preferentially removing specific ions from waters with complex compositions. The selectivity towards certain species in CDI is most frequently achieved through novel electrode materials with high affinities towards targeted species. In this study, we investigate the selective removal of fluoride ions from groundwater containing concentrated co-existing chloride ions. A carbon nanotube-CeO 2 (CNT-CeO 2) electrode is employed for the electro-sorption of fluoride ions. Our findings are compelling: when processing a mixed F−/Cl− solution comprising 10 mg/L F− and 100 mg/L Cl−, the CNT-CeO 2 electrode is seen to reduce the concentration of F− ions to 1.5 mg/L in just 150 min, amounting to an 85 % F− removal efficiency, while the Cl− removal efficiency remains below 2 %. Importantly, this translates to a F−/Cl− separation factor of up to 4.16 when using the CeO 2 -based electrodes, which is 40 times higher than that achieved with conventional activated carbon (AC) electrodes. Furthermore, the energy consumption for treating actual groundwater using scaled-up equipment is impressively low at approximately 0.2 kWh/m3. The high affinity of CNT-CeO 2 towards fluoride is attributed to the intercalation Faraday capacitance initiated by the reaction between F− with CeO 2 , as verified by the electrochemical quartz crystal microbalance (EQCM). Moreover, EQCM results show a substantial increase in both mass and current as the potential increased beyond 0.8 V vs Ag/AgCl, implying that the current surge is not a result of water splitting but rather the adsorption of F− onto the CNT-CeO 2 electrode. The addition of CNTs substantially increases the conductivity of CeO 2 electrodes and restricts the aggregation of CeO 2 , thereby accelerating ion diffusion and promoting selective adsorption characteristics. Importantly, our electro-driven approach demonstrates excellent adsorption–desorption over 20 cycles. This comprehensive study advances the technological development of selective CDI, while providing new insights for fluoride removal in groundwater. [ABSTRACT FROM AUTHOR]