Designing metallic iron based water filters: Light from methylene blue discoloration

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.

Section: Filter Designmentioning

confidence: 99%

Section: Steel Wool Filters For Allmentioning

confidence: 99%

Technologies for Decentralized Fluoride Removal: Testing Metallic Iron-based Filters

Ndé-Tchoupé

Crane

Mwakabona

et al. 2015

“…There are myriad abiotic chemical reactions likely to occur in Fe 0 /H 2 O systems (Equation (30) through Equation (44)). Equation (30) accelerates Fe 0 corrosion by consuming Fe 2+ (LeChatelier) and thus increasing the production of iron oxides/hydroxides for Cr VI adsorption and co-precipitation. Equation (31) [137].…”

Section: Overview Of Reactions Of Engineering Importancementioning

confidence: 99%

“…ZVI is in essence an ill-defined material encompassing all Fe 0 -based alloys, commercially available as "granular iron", "iron filings", "iron chips", and "iron shavings", etc. [6,26,28,30,31]. Even though Fe 0 reactivity toward both inorganic and organic substances was reported much earlier by an important number of works [13,15,17,21,[32][33][34], the use of Fe 0 as a reactive material for water remediation received a great deal of attention only at the beginning of the 1990s, after the publication of the first experimental studies focused on the degradation of chlorinated aliphatics [35][36][37][38][39].…”

Section: Introductionmentioning

confidence: 99%

Progress in Understanding the Mechanism of CrVI Removal in Fe0-Based Filtration Systems

Gheju¹

2018

Hexavalent chromium (Cr VI ) compounds are used in a variety of industrial applications and, as a result, large quantities of Cr VI have been released into the environment due to inadequate precautionary measures or accidental releases. Cr VI is highly toxic to most living organisms and a known human carcinogen by inhalation route of exposure. Another major issue of concern about Cr VI compounds is their high mobility, which easily leads to contamination of surface waters, soil, and ground waters. In recent years, attention has been focused on the use of metallic iron (Fe 0 ) for the abatement of Cr VI polluted waters. Despite a great deal of research, the mechanisms behind the efficient aqueous Cr VI removal in the presence of Fe 0 (Fe 0 /H 2 O systems) remain deeply controversial. The introduction of the Fe 0 -based filtration technology, at the beginning of 1990s, was coupled with the broad consensus that direct reduction of Cr VI by Fe 0 was followed by co-precipitation of resulted cations (Cr III , Fe III ). This view is still the dominant removal mechanism (reductive-precipitation mechanism) within the Fe 0 remediation industry. An overview on the literature on the Cr geochemistry suggests that the reductive-precipitation theory should never have been adopted. Moreover, recent investigations recalling that a Fe 0 /H 2 O system is an ion-selective one in which electrostatic interactions are of primordial importance is generally overlooked. The present work critically reviews existing knowledge on the Fe 0 /Cr VI /H 2 O and Cr VI /H 2 O systems, and clearly demonstrates that direct reduction with Fe 0 followed by precipitation is not acceptable, under environmental relevant conditions, as the sole/main mechanism of Cr VI removal in the presence of Fe 0 .

“…Relevant tools include adding oxidizing agents to accelerate corrosion [58], increasing flow velocity [34] and using Fe 0 of smaller particle sizes and/or rapid small-scale column tests [65]. For the early phase of column operation, methylene blue (MB) discoloration has been proven a powerful indicator of reactivity [68][69][70][71][72][73][74]. Actually, the longest experiment with MB in this context lasted only for 4 months [69].…”

Section: (Section 2)mentioning

confidence: 99%

Predicting the Hydraulic Conductivity of Metallic Iron Filters: Modeling Gone Astray

Noubactep

2016

Abstract:Since its introduction about 25 years ago, metallic iron (Fe 0 ) has shown its potential as the key component of reactive filtration systems for contaminant removal in polluted waters. Technical applications of such systems can be enhanced by numerical simulation of a filter design to improve, e.g., the service time or the minimum permeability of a prospected system to warrant the required output water quality. This communication discusses the relevant input quantities into such a simulation model, illustrates the possible simplifications and identifies the lack of relevant thermodynamic and kinetic data. As a result, necessary steps are outlined that may improve the numerical simulation and, consequently, the technical design of Fe 0 filters. Following a general overview on the key reactions in a Fe 0 system, the importance of iron corrosion kinetics is illustrated. Iron corrosion kinetics, expressed as a rate constant k iron , determines both the removal rate of contaminants and the average permeability loss of the filter system. While the relevance of a reasonable estimate of k iron is thus obvious, information is scarce. As a conclusion, systematic experiments for the determination of k iron values are suggested to improve the database of this key input parameter to Fe 0 filters.