The use of zero-valent iron for groundwater remediation and wastewater treatment: a review.

Reusability of iron sludge as an iron source for the electrochemical Fenton-type process using Fe²+/HOCl system.

Water treatment with metallic iron (Fe0) is still based on the premise that Fe0 is a reducing agent. An alternative concept stipulates that contaminants are removed by adsorption, co-precipitation, and size-exclusion in a reactive filtration process. This article underlines the universal validity of the alternative concept. It is shown that admixing non-expansive material to Fe0 as a pre-requisite for sustainable Fe0-based filtration systems. Fe0-based filters are demonstrated an affordable, appropriate, and efficient decentralized water treatment technology.

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Metallic Iron for Water Treatment: A Critical Review

Application of zero-valent iron nanoparticles (nZVI) for Zn2+ removal and its mechanism were discussed. It demonstrated that the uptake of Zn2+ by nZVI was efficient. With the solids concentration of 1 g/L nZVI, more than 85% of Zn2+ could be removed within 2 h. The pH value and dissolved oxygen (DO) were the important factors of Zn2+ removal by nZVI. The DO enhanced the removal efficiency of Zn2+. Under the oxygen-contained condition, oxygen corrosion gave the nZVI surface a shell of iron (oxy)hydroxide, which could show high adsorption affinity. The removal efficiency of Zn2+ increased with the increasing of the pH. Acidic condition reduced the removal efficiency of Zn2+ by nZVI because the existing H+ inhibited the formation of iron (oxy)hydroxide. Adsorption and co-precipitation were the most likely mechanism of Zn2+ removal by nZVI. The FeOOH-shell could enhance the adsorption efficiency of nZVI. The removal efficiency and selectivity of nZVI particles for Zn2+ were higher than Cd2+. Furthermore, a continuous flow reactor for engineering application of nZVI was designed and exhibited high removal efficiency for Zn2+.

Application of zero-valent iron nanoparticles for the removal of aqueous zinc ions under various experimental conditions.

Removal of critical metals from waste water by zero-valent iron

Mechanism of zinc iron removal by zero-valent iron was discussed through zinc removal responses to several operational conditions of a packed column reactor with zero-valent iron powder. The adsorption isotherm observed implied that a kind of chemisorption was responsible for zinc removal. Zinc removal by zero-valent iron was enhanced by dissolved oxygen and ferric ion addition. However, it was deteriorated under acidic pH. In addition, zinc adsorbed on zero-valent iron was eluted by a reducing agent such as citric acid, whereas the zinc was not eluted by diluted sulfuric acid. Consequently, the zinc removal mechanism by zero-valent iron was inferred to be as follows: Zero-valent iron was firstly corroded and oxidized into ferric ion by dissolved oxygen. The ferric ion was precipitated as iron hydroxide onto the surface of the zero-valent iron powder. Zinc ion was adsorbed on and/or coprecipitated with the iron hydroxide. The iron hydroxide was finally oxidized and transformed into iron oxides.

Youhei Narazaki

Papers

Mechanistic Consideration of Zinc Ion Removal by Zero-Valent Iron

Reusability of zero-valent iron particles for zinc ion separation