Ferrous Iron Removal Promotes Microbial Reduction of Crystalline Iron(III) Oxides

Bio-beneficiation of ores through iron removal is a common technique, but not yet tested for the case of bauxite. In this study we compared the iron reducing ability of three bacterial species with and without the chelating action of EDTA. Tests were carried out using a diasporic bauxite sample containing 19.3% Fe2Ο3 in the form of hematite, goethite and chamosite. Reductive dissolution was attempted using three neutrophilic, dissimilatory Fe(III) respirators, i.e. the facultative anaerobes Shewanella putrefaciens and Ferrimonas balearica and the strict anaerobe Desulfuromonas palmitatis. Almost 25% of Fe was reduced by D. palmitatis and S. putrefaciens and 30% by F. balearica in bauxite samples. In the case of S. putrefaciens and F. balearica, Fe(III) reduction took place without addition of EDTA, but most of the biologically produced Fe(II) reprecipitated. The addition of EDTA proved to hinder the bioreduction potential for both S. putrefaciens and F. balearica. On the contrary, D. palmitatis was able to reduce Fe(III) oxides only in the presence of EDTA. Moreover, the presence of EDTA helped maintain biogenic ferrous iron in solution.

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Ferrihydrite-Dependent Growth of Sulfurospirillum deleyianum through Electron Transfer via Sulfur Cycling

Applied and Environmental Microbiology ◽

10.1128/aem.70.10.5744-5749.2004 ◽

2004 ◽

Vol 70 (10) ◽

pp. 5744-5749 ◽

Cited By ~ 79

Author(s):

Kristina L. Straub ◽

Bernhard Schink

Keyword(s):

Electron Acceptor ◽

Ferrous Iron ◽

Iron Reduction ◽

Ferric Iron ◽

Sulfide Oxidation ◽

Microbial Reduction ◽

Sulfur Cycle ◽

Sulfur Cycling ◽

Sulfur Source ◽

Sulfur Species

ABSTRACT Observations in enrichment cultures of ferric iron-reducing bacteria indicated that ferrihydrite was reduced to ferrous iron minerals via sulfur cycling with sulfide as the reductant. Ferric iron reduction via sulfur cycling was investigated in more detail with Sulfurospirillum deleyianum, which can utilize sulfur or thiosulfate as an electron acceptor. In the presence of cysteine (0.5 or 2 mM) as the sole sulfur source, no (microbial) reduction of ferrihydrite or ferric citrate was observed, indicating that S. deleyianum is unable to use ferric iron as an immediate electron acceptor. However, with thiosulfate at a low concentration (0.05 mM), growth with ferrihydrite (6 mM) was possible and sulfur was cycled up to 60 times. Also, spatially distant ferrihydrite in agar cultures was reduced via diffusible sulfur species. Due to the low concentrations of thiosulfate, S. deleyianum produced only small amounts of sulfide. Obviously, sulfide delivered electrons to ferrihydrite with no or only little precipitation of black iron sulfides. Ferrous iron and oxidized sulfur species were produced instead, and the latter served again as the electron acceptor. These oxidized sulfur species have not yet been identified. However, sulfate and sulfite cannot be major products of ferrihydrite-dependent sulfide oxidation, since neither compound can serve as an electron acceptor for S. deleyianum. Instead, sulfur (elemental S or polysulfides) and/or thiosulfate as oxidized products could complete a sulfur cycle-mediated reduction of ferrihydrite.

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An experimental study on iron removal with ferric sludge recycling

Water Science & Technology ◽

10.2166/wst.2000.0344 ◽

2000 ◽

Vol 42 (1-2) ◽

pp. 393-397 ◽

Cited By ~ 2

Author(s):

N. Tufekci ◽

H.Z. Sarikaya ◽

I. Ozturk

Keyword(s):

Reaction Kinetics ◽

Ferrous Iron ◽

Natural Waters ◽

Ferric Iron ◽

Ferric Hydroxide ◽

Iron Removal ◽

Aeration Tank ◽

Batch Reactors ◽

High Concentration ◽

Activated Sludge Processes

An iron removal process, which makes use of the catalytic effect of ferric iron, is proposed. For this purpose, the reaction kinetics derived from the data of the batch experiments was applied to the continuous flow system. Based upon this reaction kinetics, it has been theoretically demonstrated that the volumes of aeration tanks can be significantly reduced by keeping a high concentration of ferric iron in the reactor. However, in natural waters, Fe(II) is found commonly to be in the range of 0.01–10 mg/l. These ferrous iron concentrations are not high enough to maintain the high concentrations of ferric iron in the aeration tank. Therefore, similar to the activated sludge processes used in wastewater treatment, it is suggested that the required Fe(III) concentrations can be maintained by recycling Fe(OH)3 sludge back to the aeration tank. It is known that the oxygenation of ferrous iron is catalyzed by the reaction product, ferric hydroxide. Catalytic action of the ferric iron sludges on the oxidation of ferrous iron by aeration has been identified and the kinetics of this catalytic reaction has been formulated by the authors. The oxidation of Fe(II) was studied in batch reactors in which the concentration of Fe(III) was in the range of 0–600 mg/l. The oxygenation rate increased linearly with the increasing Fe(III) concentrations up to 50 mg/l and a second-order polynomial relationship was found between the reaction rate and the Fe(III) concentrations in the range of 50–600 mg/l. The required volume (V) of the aeration tank and the effluent Fe(II) concentrations were determined as a function of the Fe(III) concentration. The volume of the aeration tank required for the same Fe(II) conversion was reduced by a factor of 15 when the Fe(III) concentration was raised from 0 to 600 mg/l at pH=6.7. No incremental benefit of the increase of Fe(III) concentration was observed at Fe(III) levels beyond the 600 mg/l. This study has experimentally demonstrated that significant savings can be achieved in iron removal systems by recirculating the Fe(III) sludges back to the aeration tank.

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Ferrous iron removal by limestone and crushed concrete in dynamic flow columns

Journal of Environmental Management ◽

10.1016/j.jenvman.2013.02.018 ◽

2013 ◽

Vol 124 ◽

pp. 165-171 ◽

Cited By ~ 9

Author(s):

Yu Wang ◽

Saraya Sikora ◽

Timothy G. Townsend

Keyword(s):

Ferrous Iron ◽

Iron Removal ◽

Dynamic Flow ◽

Crushed Concrete

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Microbially Mediated Coupling of Fe and N Cycles by Nitrate-Reducing Fe(II)-Oxidizing Bacteria in Littoral Freshwater Sediments

Applied and Environmental Microbiology ◽

10.1128/aem.02013-17 ◽

2017 ◽

Vol 84 (2) ◽

Cited By ~ 10

Author(s):

Franziska Schaedler ◽

Cindy Lockwood ◽

Ulf Lueder ◽

Clemens Glombitza ◽

Andreas Kappler ◽

...

Keyword(s):

Nitrate Reduction ◽

Ferrous Iron ◽

Iron Oxidation ◽

Global Scale ◽

Microbial Reduction ◽

Metal Mobility ◽

Freshwater Sediments ◽

Oxidation Rates ◽

Expression Of Genes ◽

Underlying Mechanisms

ABSTRACTNitrate-reducing iron(II)-oxidizing bacteria have been known for approximately 20 years. There has been much debate as to what extent the reduction of nitrate and the oxidation of ferrous iron are coupled via enzymatic pathways or via abiotic processes induced by nitrite formed by heterotrophic denitrification. The aim of the present study was to assess the coupling of nitrate reduction and iron(II) oxidation by monitoring changes in substrate concentrations, as well as in the activity of nitrate-reducing bacteria in natural littoral freshwater sediment, in response to stimulation with nitrate and iron(II). In substrate-amended microcosms, we found that the biotic oxidation of ferrous iron depended on the simultaneous microbial reduction of nitrate. Additionally, the abiotic oxidation of ferrous iron by nitrite in sterilized sediment was not fast enough to explain the iron oxidation rates observed in microbially active sediment. Furthermore, the expression levels of genes coding for enzymes crucial for nitrate reduction were in some setups stimulated by the presence of ferrous iron. These results indicate that there is a direct influence of ferrous iron on bacterial denitrification and support the hypothesis that microbial nitrate reduction is stimulated by biotic iron(II) oxidation.IMPORTANCEThe coupling of nitrate reduction and Fe(II) oxidation affects the environment at a local scale, e.g., by changing nutrient or heavy metal mobility in soils due to the formation of Fe(III) minerals, as well as at a global scale, e.g., by the formation of the primary greenhouse gas nitrous oxide. Although the coupling of nitrate reduction and Fe(II) oxidation was reported 20 years ago and has been studied intensively since then, the underlying mechanisms still remain unknown. One of the main knowledge gaps is the extent of enzymatic Fe(II) oxidation coupled to nitrate reduction, which has frequently been questioned in the literature. In the present study, we provide evidence for microbially mediated nitrate-reducing Fe(II) oxidation in freshwater sediments. This evidence is based on the rates of nitrate reduction and Fe(II) oxidation determined in microcosm incubations and on the effect of iron on the expression of genes required for denitrification.

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