Molecular-Level Processes Governing the Interaction of Contaminants with Iron and Manganese Oxides

Cr(VI) Reduction and Immobilization by Magnetite under Alkaline pH Conditions: The Role of Passivation

“…For the Cr(VI)-and Cr(III)-containing model compounds, Peterson et al (23) determined the Cr(VI)-O distance to be 1.63 ( 0.03 Å and the Cr(III)-O distance to be 1.99 Å. In investigating the reaction of Cr(VI) with magnetite, Peterson et al (24) showed the distance between Cr and its nearest shell of oxygen atoms to be 1.98 ( 0.01 Å. Second-shell distances between Cr and Cr and/or Fe atoms were 3.01 ( Passivation is an important process in heterogeneous redox reactions and is observed for redox reactions involving magnetite, green rust, and zero-valent iron (27,28). In studies of Fe(0)-induced reduction of Cr(VI), Chambers (27) found Fe 0 was coated with a thin oxide skin consisting mostly of magnetite.…”

“…Similar problems with surface oxidation and passivation are likely to occur in the application of zero-valent metal for in situ remediation strategies. There are numerous studies investigating Fe(0) for remediation of groundwaters contaminated by chromate, arsenic and organic contaminants (20,27). Many of these studies have observed that the reductive capacity of zerovalent Fe degrades over time, and some authors have postulated that ferrous or ferric reaction products precipitate on the metal, slowing the contaminant reduction rates (20).…”

“…Role of Passivation and Cr(VI) Reduction. Passivation is an important process in heterogeneous redox reactions and is observed for redox reactions involving magnetite, green rust, and zero-valent iron ( , ). In studies of Fe(0)-induced reduction of Cr(VI), Chambers () found Fe 0 was coated with a thin oxide skin consisting mostly of magnetite.…”

“…In studies of Fe(0)-induced reduction of Cr(VI), Chambers (27) found Fe 0 was coated with a thin oxide skin consisting mostly of magnetite. The redox process converted magnetite and zero-valent iron, which are conductive and facilitate electron-transfer processes, to an insulating iron(III)-chromium(III) oxyhydroxide.…”

Biotite dissolution and Cr(VI) reduction at elevated pH and ionic strength

“…A surface passivation effect has been observed in studies of heterogeneous Cr(VI) reduction by magnetite, Fe(0), and green rust (Chambers, 1996;Peterson et al, 1996;Peterson et al, 1997;Kendelewicz et al, 2000;Williams and Scherer, 2001). In systems containing Fe(II)-phyllosilicates, secondary aluminosilicates, Al-(hydr)oxides, or Fe-(hyr)oxides might armor the surface against further hydroxyl attack and inhibit dissolution, resulting in less Cr(VI) reduction.…”