Iron microbiological reduction

Siderite is a common mineral in mires, where it is formed through microbiological reduction of iron oxides in the environment. This mechanism may explain its occurrence on artefacts that have lain exposed on the mire surface for a period of time. In these conditions they will be quickly covered by a layer of iron oxides, which will subsequently be reduced to siderite after being overgrown and embedded in an anoxic environment. However, for other artefacts (and modem samples) that have been placed directly under anoxic conditions the siderite must have formed directly from the metallic iron, and here it is still unclear exactly what cathodic reaction is responsible for the oxidation of iron. A Pourbaix diagram based on the actual soil conditions at Nydam is shown in Figure 8. The hatched area in the Pourbaix diagram demonstrates that the pH values found at Nydam are close to the lower limit for siderite stability, so the soil pH is monitored intensively to be sure that no acidification takes place. 

Lovley, D. R and E. J. P. Phillips (1988), "Novel Mode of Microbial Energy Metabolism Organic Carbon Oxidation Coupled to Dissimilatory Reduction of Iron or Manganese", Applied and Environ. Microbiology 54/6, 1472-1480. 

Nealson, K. H. (1982), "Microbiological Oxidation and Reduction of Iron", in H. D. Holland and M. Schidlowski, Eds., Mineral Deposits and Evolution of the Biosphere Dahlem Konferenzen, Springer Verlag, New York, 51 -56. 

Balashova VV, Zavarzin GA. 1980. Anaerobic reduction of ferric iron by hydrogen bacteria. Microbiology 48 635-9. 

Paul FA, Qark FE (1989) Soil microbiology and biochemistry. Academic Press, New York Pecher K, HaderUne SB, Schwarzenbach RP (2002) Reduction of polyhalogenated methanes by surface— b Fe(ll) in aqueous suspensions of iron oxides. Environ Sci Technol 36 1734-1741 Penrose WR, Metta DN, Hyfko JM, Rinkel LA (1987) The reduction of plutonium (V) by aquatic sediments. J Environ Radioact 5 169-184... 

Jones, J.G. Gardener, S. Simon, B.M. (1983) Bacterial reduction of ferric iron in a stratified eutrophic lake. J. Gen. Microbiology 129 131-139... 

Figure 6. An idealized scheme for a sedimentary porous medium with pore walls covered by a biofilm. High sulfate reduction rates are maintained even in depths to which sulfate cannot diffuse because of recycling of sulfate within the biofilm. Numbered points (in black circles) denote the following processes I, Respiration consumes oxygen. 2, Microbial reduction of reactive metal Oxides. Reduction of reactive ferric oxides is in equilibrium with reoxidation of ferrous iron by Os. Thus, no net loss of reactive iron takes place in these layers. 3, Microbial reduction of ferric oxides. 4, Sulfate reduction rate (denoted as SRR). 5, Sulfide oxidation, either microbiologically or chemically. 6, Sulfide builds up within the hiofilm, sulfate consumption increases, reactive iron pool decreases. 7, Formation of iron sulfides.

Influence of Some Microbiological Species on Corrosion.64 Some bacteria are involved directly in the oxidation or reduction of metal ions, particularly iron and manganese. 

King, G. M., and Garey, M. A. (1999). Ferric iron reduction by bacteria associated with the roots of freshwater and marine macrophytes. Appl. Environ. Microbiology. 65, 4393-4398. 

Ghiorse, W. C. (1986), Microbial Reduction of Manganese and Iron, in A. J. B. Zehnder, Ed., Environmental Microbiology of Anaerobes, Wiley-Interscience, New York. 

Benz, M., Brune, A. and Schink, B., 1998. Anaerobic and aerobic oxidation of ferrous iron and neutral pH by chemoheterotrophic nitrate-reduction bacteria. Archives of Microbiology, 169 159-165. 

Thamdrup, B., Finster, K., Hansen, J.W. and Bak, F., 1993. Bacterial disproportionation of elemental sulfur coupled to chemical reduction of iron or manganese. Applied and Environmental Microbiology, 59 101-108. 

Biogeochemical conditions favoring magnetite formation during anaerobic iron reduction. Applied and Environmental Microbiology, 53 2610-2616. 

Lovley, D.R. and Phillips, E.J.P., 1988. Novel mode of microbial energy metabolism Organic carbon oxidition coupled to dissimilatory reduction of iron and manganese. Applied and Environmental Microbiology, 54 1472-1480... 

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