https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1245&context=usdoepub

Biogenic iron mineralization accompanying the dissimilatory reduction of hydrous ferric oxide by a groundwater bacterium

Leaching of nitrate from soils and sediments can be reduced in anoxic environments due to denitrification to N2O/N2 or reduction of nitrate to ammonium. While microbial dissimilatory reduction of nitrate to ammonia is well known, it is shown here that this conversion can also proceed at appreciable rates in abiotic systems in the presence of green rust compounds [FeII4FeIII2(OH)12SO4·yH2O]. In the reaction nitrate is stoichiometrically reduced to ammonium, and magnetite (Fe3O4) is the sole Fe-containing product. At a constant pH of approximately 8.25 and 25 °C, the rate expression is given as:  d[NH4+]/dt = k[Fe(II)]GR[NO3-],where k = 4.93 × 10-5 ± 0.39 × 10-5 L mol-1 s-1. In anoxic soils and sediments, this reaction may also lead to a nitrate to ammonium reduction, at rates of similar magnitude or even higher than microbial reduction rates. Hence green rust should be considered a possible important reductant for nitrate reduction to ammonium in subsoils, sediments, or aquifers where microbially mediated ...

Abiotic Nitrate Reduction to Ammonium: Key Role of Green Rust

Synthetic green rusts, GRs, are prepared by oxidation of Fe(OH)2 incorporating Cl-, SO42-, or CO32- ions. Eh−pH diagrams are drawn, and thermodynamic data are derived. A GR incorporating OH- ions, GR1(OH-), is suspected to exist like similar other M(II)−M(III) compounds. GRs form as corrosion products of steels, implying microbially induced corrosion. Mossbauer and Raman spectroscopies allowed the identification of GR in samples extracted from hydromorphic soils scattered over Brittany, France. This mineral has a varying Fe(III)/Fe(II) ratio. At Fougeres, it increases with depth till the oc currence of more oxidized ferric oxyhydroxide. In the same sites, soil solutions are collected and prevented from any oxidation and photoreduction. In large ranges of pH, pe, and Fe(II) concentration variations, soil solutions are in equilibrium with a Fe(II)−Fe(III) compound, a GR1 mineral with pyroaurite-like structure incorporating OH- ions and having the formula [FeII(1-x)FeIIIx(OH)2]+x·[xOH]-x ≡ Fe(OH)(2+x). Compu...

Thermodynamic Equilibria in Aqueous Suspensions of Synthetic and Natural Fe(II)−Fe(III) Green Rusts: Occurrences of the Mineral in Hydromorphic Soils

Mechanisms of formation and structure of green rust one in aqueous corrosion of iron in the presence of chloride ions

Mixed-valent iron [Fe(II)-Fe(III)] minerals such as magnetite and green rust have received a significant amount of attention over recent decades, especially in the environmental sciences. These mineral phases are intrinsic and essential parts of biogeochemical cycling of metals and organic carbon and play an important role regarding the mobility, toxicity, and redox transformation of organic and inorganic pollutants. The formation pathways, mineral properties, and applications of magnetite and green rust are currently active areas of research in geochemistry, environmental mineralogy, geomicrobiology, material sciences, environmental engineering, and environmental remediation. These aspects ultimately dictate the reactivity of magnetite and green rust in the environment, which has important consequences for the application of these mineral phases, for example in remediation strategies. In this review we discuss the properties, occurrence, formation by biotic as well as abiotic pathways, characterization t...

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Paul P. Stampfl

Papers

Ein basisches eisen-II-III-karbonat in rost