Fe Atom Exchange between Aqueous Fe²⁺ and Magnetite

Abstract

The reaction between magnetite and aqueous Fe(2+) has been extensively studied due to its role in contaminant reduction, trace-metal sequestration, and microbial respiration. Previous work has demonstrated that the reaction of Fe(2+) with magnetite (Fe(3)O(4)) results in the structural incorporation of Fe(2+) and an increase in the bulk Fe(2+) content of magnetite. It is unclear, however, whether significant Fe atom exchange occurs between magnetite and aqueous Fe(2+), as has been observed for other Fe oxides. Here, we measured the extent of Fe atom exchange between aqueous Fe(2+) and magnetite by reacting isotopically "normal" magnetite with (57)Fe-enriched aqueous Fe(2+). The extent of Fe atom exchange between magnetite and aqueous Fe(2+) was significant (54-71%), and went well beyond the amount of Fe atoms found at the near surface. Mössbauer spectroscopy of magnetite reacted with (56)Fe(2+) indicate that no preferential exchange of octahedral or tetrahedral sites occurred. Exchange experiments conducted with Co-ferrite (Co(2+)Fe(2)(3+)O(4)) showed little impact of Co substitution on the rate or extent of atom exchange. Bulk electron conduction, as previously invoked to explain Fe atom exchange in goethite, is a possible mechanism, but if it is occurring, conduction does not appear to be the rate-limiting step. The lack of significant impact of Co substitution on the kinetics of Fe atom exchange, and the relatively high diffusion coefficients reported for magnetite suggest that for magnetite, unlike goethite, Fe atom diffusion is a plausible mechanism to explain the rapid rates of Fe atom exchange in magnetite.

Green Fenton-like magnetic nanocatalysts: Synthesis, characterization and catalytic application

“…As proposed in the literature, we can assume that the ferrous ions, bound on the surface of iron oxide, could activate molecular oxygen via a single-electron reduction pathway producing ROS that are capable of reducing the pollutants [8,22]. Our results on singlet oxygen formation support this assumption.…”

Electron uptake by iron-oxidizing phototrophic bacteria

“…Conduction of electrons through this matrix would allow TIE-1 (and potentially other FeOBs) access to electrons from remote electron donors, including Fe(II) (Supplementary Fig. 7), via processes such as electron conduction and iron atom exchange [30][31][32] . Indeed, recent studies have shown that conductive minerals can facilitate electron transfer to microbes from remote electron donors (including other microbes) 33 .…”

Laboratory study of spectral induced polarization responses of magnetite — Fe2+ redox reactions in porous media

“…The adsorption of Ca 2+ , Ni 2+ and Fe 2+ to the magnetite surface progressively increases across this pH range (Vikesland and Valetine, 2002),. In the case of Fe 2+ , previous work on iron (oxyhydr)oxides including magnetite (Yanina and Rosso, 2008;Handler et al, 2009;Gorski et al, 2012) suggests that provided Fe 2+ can interact with the mineral surface, charge transfer can occur to the mineral lattice (see Figure 5b). We therefore infer that the influence of Fe 2+ adsorption on the phase response is likely to arise from redox reactions or charge transfer between adsorbed Fe 2+ and magnetite (such as reactions (1) and (2) described previously); the strong sensitivity of the phase peak frequency to increasing pH results from charge transfer via increasing amounts of adsorbed Fe 2+ ions.…”

“…It is an n and p type small band gap semiconductor at room temperature with the highest electrical conductivity of any oxide, of 1 -10 1 m 1 (Cornell and Schwertmann, 2003). Mobile charges within the magnetite lattice may be either electron or hole polarons situated on lattice sites occupied by Fe atoms, which migrate by electron hopping (Tsuda et al, 2000;Skomurski et al, 2010), or mobile Fe 2+ ions hopping between unoccupied lattice sites (Gorski et al, 2012). The rapid movement of such charges within the magnetite lattice gives rise to its high electrical conductivity (Skomurski et al, 2010;Gorski et al, 2012).…”

“…They proposed a mechanism of Fe 2+ (aq) adsorption, electron transfer through the bulk mineral and simultaneous mineral growth and dissolution on separate crystal faces, similar to that proposed by Yanina and Rosso (2008) for hematite. Gorski et al (2012) used a similar isotopic approach to investigate magnetite surface reactions. They confirmed isotopic exchange between aqueous Fe 2+ and magnetite at ~pH 6.0, which is consistent with surface redox reactions such as (1) and (2) above.…”