Characterizing the Reactivity of Metallic Iron for Water Treatment: H2 Evolution in H2SO4 and Uranium Removal Efficiency

Abstract

Metallic iron (Fe0) has been demonstrated as an excellent material for decentralized safe drinking water provision, wastewater treatment and environmental remediation. An open issue for all these applications is the rational material selection or quality assurance. Several methods for assessing Fe0 quality have been presented, but all of them are limited to characterizing its initial reactivity. The present study investigates H2 evolution in an acidic solution (pH 2.0) as an alternative method, while comparing achieved results to those of uranium removal in quiescent batch experiments at neutral pH values. The unique feature of the H2 evolution experiment is that quantitative H2 production ceased when the pH reached a value of 3.1. A total of twelve Fe0 specimens were tested. The volume of molecular H2 produced by 2.0 g of each Fe0 specimen in 560 mL H2SO4 (0.01 M) was monitored for 24 h. Additionally, the extent of U(VI) (0.084 mM) removal from an aqueous solution (20.0 mL) by 0.1 g of Fe0 was characterized. All U removal experiments were performed at room temperature (22 ± 2 °C) for 14 days. Results demonstrated the difficulty of comparing Fe0 specimens from different sources and confirmed that the elemental composition of Fe0 is not a stand-alone determining factor for reactivity. The time-dependent changes of H2 evolution in H2SO4 confirmed that tests in the neutral pH range just address the initial reactivity of Fe0 materials. In particular, materials initially reacting very fast would experience a decrease in reactivity in the long-term, and this aspect must be incorporated in designing novel materials and sustainable remediation systems. An idea is proposed that could enable the manufacturing of intrinsically long-term efficient Fe0 materials for targeted operations as a function of the geochemistry.

Kanchan Arsenic Filters for Household Water Treatment: Unsuitable or Unsustainable?

“…However, from a pure analytical perspective, this suggests that, besides the variable filtration rate, the obvious discrepancies between studies (Table 3) may be due to an internally unsteady parameter (the nails' corrosion kinetics). It should be noted that these studies globally reveal that iron nails have been employed in these filters without being characterized, and no effort has been undertaken to correct this design mistake, despite the availability of testing methods in the scientific literature for decades [76][77][78][79]. Overall, the results in Table 4 support comments from Table 3 that: (i) the KAF does not always guarantee good filtered water quality (Question 1), and (ii) the KAF needs design modifications for performance improvement (Question 2).…”

Application of the Kilimanjaro Concept in Reversing Seawater Intrusion and Securing Water Supply in Zanzibar, Tanzania

“…However, recent initiatives exist to boost the capacity of locally owned companies, with conditions directing foreign companies to enter into joint ventures with local companies as among the main qualifying criteria in tendering. Researchers advocate for complete self-reliance in water supply even where "modern" technologies are to be used [75]. It makes more sense to employ skilled personnel who will train their Tanzanian colleagues than to continue considering that the local academic system is inferior to any other.…”

“…A careful look at this historical sketch shows that with the occupation by the Germans (in 1884), African engineers abandoned their art to become workers in colonial "developmental projects" [75,76]. During this German rule and the time under British rule, the colonial administration designed some water supply systems, but not primarily for Tanzanians.…”

“…In essence, from 1884 to 2000 (some 116 years), Africans ceased to be designers of their own water supply systems and even other technologies. They were and are still mostly, and at best, associated with the maintenance of installed systems, which come to Africa as part of "Technology transfer" [75]. That is the main reason why all efforts since the 1960s have literally failed.…”

Designing the Next Generation of Fe0-Based Filters for Decentralized Safe Drinking Water Treatment: A Conceptual Framework

“…The available tests for characterizing the intrinsic reactivity of Fe 0 materials are limited to short-term batch experiments, which are certainly suitable for initial material screening [33,[108][109][110][111][112][113]. Reliable tests to characterize the long-term reactivity of Fe 0 are yet to be developed [30,33,114]. If rationally selected Fe 0 is tested during one year and corresponding treatability tests performed for one other year (Table 3), researchers will come up in two years with an array of applicable Fe 0 filters.…”