A commercial granular metallic iron (Fe0) specimen was used to evaluate the suitability of Fe0 materials for removing aqueous fluoride (F-) (water defluoridation). Experiments were performed to characterize the defluoridation potential of the tested Fe0 as influenced by the presence of chloride (Cl-) and bicarbonate (HCO3-) ions using tap water (H2O) as operational reference system. Duplicate column studies were conducted for 120 days (4 months) using an initial F- concentration of 22.5 mg L-1, columns flow rates were about 17 mL h-1. Each column contained a reactive layer (11 cm) made up of 100 g of Fe0 in a 1:1 volumetric Fe0:sand mixture. The reactive layer was sandwiched between two layers of the same sand. A pure sand column was used as control system. After the F- removal experiments, the columns were flushed by methylene blue (MB) and Orange II for 21 days. Removal studies revealed (i) no F- removal in the control system, (ii) no F- significant removal on the Cl- system, (iii) limited F- removal in the HCO3- system, and (iv) the best F- removal efficiency in tap water (H2O). Dye flushing studies confirmed the ion-selective nature of the Fe0/H2O system and demonstrated the relatively low efficiency of the same for F- removal. The overall results challenge the prevailing perception that water defluoridation using granular Fe0 is not possible and suggest that effective water defluoridation in Fe0 packed-beds is pure a site-specific design issue.
Keywords: Fluoride determination; Frugal innovation; Packed-bed adsorption; Water defluoridation; Zero-valent iron.
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