Fe(II) Redox Chemistry in the Environment

Abstract

Iron (Fe) is the fourth most abundant element in the earth's crust and plays important roles in both biological and chemical processes. The redox reactivity of various Fe(II) forms has gained increasing attention over recent decades in the areas of (bio) geochemistry, environmental chemistry and engineering, and material sciences. The goal of this paper is to review these recent advances and the current state of knowledge of Fe(II) redox chemistry in the environment. Specifically, this comprehensive review focuses on the redox reactivity of four types of Fe(II) species including aqueous Fe(II), Fe(II) complexed with ligands, minerals bearing structural Fe(II), and sorbed Fe(II) on mineral oxide surfaces. The formation pathways, factors governing the reactivity, insights into potential mechanisms, reactivity comparison, and characterization techniques are discussed with reference to the most recent breakthroughs in this field where possible. We also cover the roles of these Fe(II) species in environmental applications of zerovalent iron, microbial processes, biogeochemical cycling of carbon and nutrients, and their abiotic oxidation related processes in natural and engineered systems.

Appraisal of foliar spray of iron and salicylic acid under artificial magnetism on morpho-physiological attributes of pea (Pisum sativum L.) plants

“…Iron (Fe) is 4 th most abundant element on the earth and found in the crystal lattices of most minerals [ 30 ]. Fe in plants is mostly in Fe (III) form and very less in Fe (II) form, and most of the Fe about 90% found in chloroplast and particularly in chloroplasts of those leaves which undergo rapid growth [ 31 ].…”

Effect of Environmental pH on Mineralization of Anaerobic Iron-Oxidizing Bacteria

“…That is why the final mineralized product of Rhodobacter ferrooxidans strain SW2 is goethite with low crystallinity. The structure of the final mineralized products of the two strains was nearly identical, and the influence of environmental pH on them was similar, that is, the lower the initial pH value of the medium, the worse the crystallinity, because higher pH would increase the adsorption and reactivity of microorganisms to Fe 2+ (Huang et al, 2021 ).…”

“…In addition, environmental pH can directly affect the precipitation of iron ions in the process of iron oxidation. It can also influence the types of Fe(II) species formed and enhance their reactivity when pH increases (Huang et al, 2021 ). For example, Rhodopseudomonas palustris TIE-1 was shown to form different mineralized products under distinct pH pressures (Jiao and Newman, 2007 ), and poorly crystalline Fe(III) oxyhydroxides and goethite can be formed at low pH, while magnetite was observed at high pH (Bryce et al, 2018 ).…”

Growth of microaerophilic Fe(II)‐oxidizing bacteria using Fe(II) produced by Fe(III) photoreduction

“…Various biogeochemical interactions lead to cycling of Fe between its two main redox states +2 and +3 impacting its mobility, speciation, and bioavailability (Kappler et al, 2021). For instance, at circumneutral pH and air saturation, ferrous iron (Fe(II)) gets rapidly chemically oxidized by oxygen (O 2 ) and usually precipitates as poorly soluble Fe(III) (oxyhydr)oxides (Davison & Seed, 1983; Huang et al, 2021; Millero et al, 1987; Tamura et al, 1976). The rate of Fe(II) oxidation depends, among other factors, on pH, concentration of dissolved O 2 and is catalyzed by the autocatalytic effect of Fe(III) mineral surfaces (Millero et al, 1987; Tamura et al, 1976).…”

“…precipitates as poorly soluble Fe(III) (oxyhydr)oxides (Davison & Seed, 1983;Huang et al, 2021;Millero et al, 1987;Tamura et al, 1976). The rate of Fe(II) oxidation depends, among other factors, on pH, concentration of dissolved O 2 and is catalyzed by the autocatalytic effect of Fe(III) mineral surfaces (Millero et al, 1987;Tamura et al, 1976).…”