Abstract
Since the realization in the 1930s that elevated fluoride concentrations in drinking water can have detrimental effects on human health, new methods have been progressively developed in order to reduce fluoride to acceptable levels. In the developing world the necessity for filtration media that are both low-cost and sourced from locally available materials has resulted in the widespread use of bone char. Since the early 1990s metallic iron (Fe0) has received widespread use as both an adsorbent and a reducing agent for the removal of a wide range of contaminant species from water. The ion-selectivity of Fe0 is dictated by the positively charged surface of iron (hydr)oxides at circumneutral pH. This suggests that Fe0 could potentially be applied as suitable filter media for the negatively charged fluoride ion. This communication seeks to demonstrate from a theoretical basis and using empirical data from the literature the suitability of Fe0 filters for fluoride removal. The work concludes that Fe0-bearing materials, such as steel wool, hold good promise as low-cost, readily available and highly effective decentralized fluoride treatment materials.
Highlights
The realization that elevated fluoride levels in drinking water can cause tooth enamel degradation dates back to 1931 [1]
Literature reports that tea leaves could quantitatively remove fluoride from a aqueous 20 mg/L solution [55], Tamarind (Tamarindus indica) fruit cover powder treated with HCl could remove up to 57.1% of fluoride from natural water containing 3.5 mg/L Fat the pH of 7.6 [47]
For cases where adsorbents are generated in situ (e.g., Fe0 /H2 O system), the situation may be different because continuously generated adsorbents separately remove fluoride ions and concurrent species (Cl, HCO3 ́, NO3 ́, PO4 3 ́, SO4 2 ́ )
Summary
The realization that elevated fluoride levels in drinking water can cause tooth enamel degradation (via dental fluorosis) dates back to 1931 [1]. This discovery subsequently obliged two U.S cities (Bauxite, Arkansas and Oakley, Idaho) to discard abundant water supplies in favor of those containing lower fluoride concentrations [2]. Attempts to optimize the AA efficiency for safe drinking water provision include the development of oxide mixtures (Fe2 O3 , MgO, MnO2 , TiO2 ) [21,22] These operations appear to have been successful, but the mechanisms are still unknown [13]
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