Fluoride removal from aqueous solutions by spherical agglomeration using aluminum hydroxide and Agave salmiana extract

Groundwater contamination with fluoride is one of the most important and serious environmental concerns due to its toxicity. This study aimed to assess spherical agglomeration technique’s (SAT) efficacy in fluoride removal. Experiments were performed in acrylic containers with baffles to promote particle impacts, using 250 mL of 5.0 mg/L fluoride solution, under 300 rpm agitation, pH of 7, and room temperature. Experiments were started by adding, as fluoride adsorbents, either activated alumina (AA) or freshly prepared aluminum hydroxide (FPAH) in three doses: 0.1, 0.15 and 0.2 g/L. Once best adsorbent was selected, SAT was applied. Hydrophilization of the precipitates was performed by saponin rich Agave salmiana extracts at doses between 0.3 and 0.9 gExt/gPoll. Hydrophobized precipitates were then covered with N-heptane and finally with CaCl2 to neutralize charges and agglomerate precipitates. Best fluoride removal (89.5%) was achieved when FPAH was used in the highest tested dose (0.2 g/L). Regarding agave extract, the lowest dose (0.3 gExt/gPoll) proved the most efficient. Final fluoride concentration in mentioned conditions, resulted within the limits allowed by the regulations established for fluoride. SAT has been successfully applied for the removal of a non-metallic element such as fluoride in aqueous models.