Enhanced Removal Of Fluoride By Polystyrene Anion Exchanger Supported Hydrous Zirconium Oxide Nanoparticles

Water pollution by fluoride is a global environmental problem. Adsorption is one of the most effective methods for defluoridation from water. However, the available adsorbents such as activated alumina (AA) and anion exchangers are still facing some technical bottlenecks in adsorption preference, mechanical stability, and reusability. In this study, we synthesized ultra-fine powder HZO by modified precipitation methods, and studied its adsorption capacity toward fluoride as compared to hydrated ferric oxide (HFO), AA, and ZrO2. Subsequently, we fabricated a novel nanocomposite adsorbent HZO-201, i.e., nanosized hydrous zirconium oxide (HZO) encapsulated within a commercial porous polystyrene anion exchanger D201, for highly efficient defluoridation of water. HZO-201 exhibited much higher preference than AA and D201 toward fluoride removal when competing anions (chloride, sulfate, nitrate, and bicarbonate) coexisted at relatively high levels. Fixed column adsorption indicated that the effective treatable volume of water with HZO-201 was about 7～14 times as much as with D201 irrespective of whether synthetic solution or groundwater was the feeding solution. In addition, HZO-201 could treat>3000 BV of the acidic effluent (around 3.5 mg F-/L) per run at pH 3.5, compared to only～4 BV with D201. The exhausted HZO-201 could be regenerated by NaOH solution for repeated use without any significant capacity loss. Such attractive performance of HZO-201 resulted from its specific hybrid structure, that is, the host anion exchanger D201 favors the preconcentration of fluoride ions inside the polymer based on the Donnan principle, and the encapsulated nanosized HZO exhibits preferable sequestration of fluoride through specific interaction, as further demonstrated by XPS spectra. The influence of solution pH, competitive anions, and contact time was also examined, and a small-scale field test was also carried out in Yunnan China. All results suggested that HZO-201 has a great potential in efficient defluoridation of groundwater and acidic mine drainage.