Evaluation of Aluminum Hydroxide-Amended Zeolites in Fluoride Removal: Column Filtration and Regeneration

Pure aluminum (hydr)oxide (AlOOH) and AlOOH-amended sodalite exhibited good performance in column fluoride removal studies in terms of service time (time until breakthrough), energy required for operation, and cost. The long service times (2,000 and 1,370 bed volumes for pure AlOOH and AlOOH-amended sodalite, respectively) were due to the relatively large mass loading of AlOOH, as well as the formation of a very adsorptive amorphous AlOOH phase at a slightly acidic pH (5.3). There was significant aluminum release from the columns during the first 70 bed volumes, which was attributed to outflow of AlOOH particles. Subsequently, the effluent aluminum concentration stayed below 0.2 mg/L until breakthrough, after which it increased, possibly due to fluoride-induced AlOOH dissolution and formation of aqueous aluminum–fluoride complexes. The pumping energy required to treat 1 m3 of water using AlOOH-amended sodalite in a community-scale filter (approximately 2.2×10−2 kWh/m3) is two orders of magnitude lower than the energy required to operate electrocoagulation and reverse osmosis, and is favorable for the practical use of AlOOH-amended sodalite. In the absence of a continuous power supply, hydrostatic energy could also be used to run a community-scale filter using an elevated water tank. The relatively low cost of these materials (e.g., $1.05 to produce sufficient AlOOH-amended sodalite to treat 1 m3 of water) makes them appealing for use in developing regions. The overall materials costs can be further decreased by regeneration with 0.01 M sodium hydroxide.