Abstract

In bioreactor systems for the treatment of metal-contaminated water, pretreatment with zerovalent Fe can be exploited for oxygen consumption and H2 production. In this study, a column experiment is used to investigate the changes in surface chemistry and solid phase products that result from the reaction of a Zn-sulphate-lactate solution with zerovalent Fe filings. The results of this study indicate that zerovalent Fe is very effective in immobilizing dissolved Zn with a porewater residence time of 1.3–3.1 days. A combination of X-ray diffractometry, X-ray photoelectron spectroscopy, and mineral equilibria calculations indicates that Zn precipitates as Zn(OH)2 and zincite at pH 9–10. At pH ≈6, Zn primarily adsorbs to abundant ferric oxyhydroxides, although incorporation in green rust is also considered. During the course of the experiment, the surface mineralogy changes from magnetite-lepidocrocite-goethite to green rust-akaganéite-goethite. The results suggest that the zerovalent Fe surface becomes passivated by a surface film of ferric oxyhydroxides, green rust and organic material, so that the rate of electron transfer and proton consuming reactions (i.e. oxygen consumption, H2 generation) declines, resulting in a decrease in solution pH.

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