Metallic iron (Fe0) materials have been industrially used for water treatment since the 1850s. There are still many fundamental challenges in affordably and reliably characterizing the Fe0 intrinsic reactivity. From the available methods, the one using Fe0 dissolution in ethylenediaminetetraacetic acid (EDTA—2 mM) was demonstrated the most applicable as it uses only four affordable chemicals: Ascorbic acid, an ascorbate salt, EDTA and 1,10-Phenanthroline (Phen). A careful look at these chemicals reveals that EDTA and Phen are complexing agents for dissolved iron species. Fe3-EDTA is very stable and difficult to destabilize; ascorbic acid is one of the few appropriate reducing agents, therefore. On the other hand, the Fe2-Phen complex is so stable that oxidation by dissolved O2 is not possible. This article positively tests Fe0 (0.1 g) dissolution in 2 mM Phen (50 mL) as a characterization tool for the intrinsic reactivity, using 9 commercial steel wool (Fe0 SW) specimens as probe materials. The results are compared with those obtained by the EDTA method. The apparent iron dissolution rate in EDTA (kEDTA) and in Phen (kPhen) were such that 0.53 ≤ kEDTA (μg h−1) ≤ 4.81 and 0.07 ≤ kPhen (μg h−1) ≤ 1.30. Higher kEDTA values, relative to kPhen, are a reflection of disturbing Fe3 species originating from Fe2 oxidation by dissolved O2 and dissolution of iron corrosion products. It appears that the Phen method considers only the forward dissolution of Fe0. The Phen method is reliable and represents the most affordable approach for characterizing the suitability of Fe0 for water treatment.

No abstract

Metallic iron (Fe 0 )-based filtration systems have the potential to significantly contribute to the achievement of the United Nations (UN) Sustainable Development Goals (SDGs) of substantially improving the human condition by 2030 through the provision of clean water. Recent knowledge on Fe 0 -based safe drinking water filters is addressed herein. They are categorized into two types: Household and community filters. Design criteria are recalled and operational details are given. Scientists are invited to co-develop knowledge enabling the exploitation of the great potential of Fe 0 filters for sustainable safe drinking water provision (and sanitation).

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 (Fe 0 ) 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 Fe 0 is dictated by the positively charged surface of iron (hydr)oxides at circumneutral pH. This suggests that Fe 0 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 Fe 0 filters for fluoride removal. The work concludes that Fe 0 -bearing materials, such as steel wool, hold good promise as low-cost, readily available and highly effective decentralized fluoride treatment materials.

Researchers on metallic iron (Fe 0

No abstract

Studies were undertaken to determine the reasons why published information regarding the efficiency of metallic iron (Fe 0 ) for water treatment is conflicting and even confusing. The reactivity of eight Fe 0 materials was characterized by Fe dissolution in a dilute solution of ethylenediaminetetraacetate (Na 2 -EDTA; 2 mM). Both batch (4 days) and column (100 days) experiments were used. A total of 30 different systems were characterized for the extent of Fe release in EDTA. The effects of Fe 0 type (granular iron, iron nails and steel wool) and pretreatment procedure (socking in acetone, EDTA, H 2 O, HCl and NaCl for 17 h) were assessed. The results roughly show an increased iron dissolution with increasing reactive sites (decreasing particle size: wool > filings > nails), but there were large differences between materials from the same group. The main output of this work is that available results are hardly comparable as they were achieved under very different experimental conditions. A conceptual framework is presented for future research directed towards a more processed understanding.Sustainability 2019, 11, 671 2 of 20 organic [27,28], fluoride [29][30][31], heavy metals [32,33], nitrate [34,35], pathogens [36][37][38] and radionuclides [32,39]. The desalination of water using Fe 0 has also been reported [40][41][42][43]. The two key advantages of Fe 0 are its affordability and its universal availability (iron nails, scrap iron and steel wool) [9,10,44,45]. It is commonly reported that the major drawback of Fe 0 -based technologies for water treatment is the low intrinsic reactivity of granular materials [28,33,46]. This situation is said to be aggravated by the inherent generation of an oxide scale at the Fe 0 surface (passivation). Countermeasures to overcome Fe 0 passivation were recently reviewed by Guan et al. [28] and further discussed by Noubactep [47]. It is recalled that, considering passivation as a "curse" contradicts the evidence that Fe 0 -based subsurface permeable barriers have been successfully working for more than one decade [48][49][50]. On the other hand, increased "passivation" should have occurred in the spongy iron filters in Antwerpen as well [2,19]. Clarifying this contradiction is certainly a progress for the whole Fe 0 technology. Clearly, an understanding of the role of "passivation" in the process of decontamination using Fe 0 should be useful for enhancing the system's efficiency in practice [30,31,47].There is an agreement on the evidence that using Fe 0 for water treatment and environmental remediation is "putting corrosion to use" [51][52][53]. There is otherwise a contradiction on practically any other aspect concerning the Fe 0 /H 2 O system, including the reaction mechanisms and factors determining the long-term efficiency of such systems [9,28,47,[54][55][56][57][58]. A key reason for this is the large variability of experimental conditions used in testing Fe 0 materials [58][59][60][61][62]. The main influencing operational parameter seems to be Fe 0 itself [58,61,63,6...

Arusha aquifers have been exploited intensively serving as the main source of domestic water supply in the city. But the quality of groundwater is not clearly documented for future planning and management. Hydrogeochemical assessment was carried out to establish groundwater quality and its spatial distribution with the aid of geostatistical techniques. Groundwater samples were collected and analyzed for major cations and anions using conventional methods of water analysis. Well lithology and geological map were considered for hydrogeological interpretation of the area. The results of piper diagram revealed Na-K-HCO 3 water type with sodium and bicarbonate ions dominating in all samples. High fluoride concentrations and general groundwater chemistry are mainly controlled by aquifer lithology than anthropogenic activities. The levels of anthropogenic pollution indicators such as nitrate, chloride and sulfate in deep wells are generally low and most likely coming from natural sources. The geological sections indicate two potential aquifers (volcanic sediment and weathered/ fractured formation) both yield water containing significant concentration of fluoride. Fluoride concentrations were higher than WHO guidelines (1.5 mg/l) and Tanzanian standards (4.0 mg/l) by 82 and 36% of the analyzed groundwater samples, respectively. The southern part of the study area yields groundwater of better quality for human consumption than northern zones which is at high elevation on the foot of Mt. Meru. With exception of fluoride, the quality of groundwater in the study area is generally suitable for drinking purpose and other socioeconomic uses.