Geological iron cycle

Iron and the Environment The natural geological iron cycle comprises weathering of rocks and subsequent water-mediated re-sedimentation. The amount of mined iron exceeds the natural circulation by an estimated factor of 8. Approximately 25% of iron production is estimated to be destroyed by corrosion and dispersed into the environment. Additional iron is emitted by combustion of iron-containing coal, but approximately 70% of scrap is returned into the steel production process. The re-utilization of scrap requires 60% less energy than smelting ores. Zinc from coated steel scrap vaporizes during crude steel production and is recovered in dust filters (Ullmann 1989). 

Jonas, J.P. and Gammons, C.H. (2000) Iron cycling in the Berkeley Pit-lake, Butte, Montana. Abstracts with Programs. The Geological Society of America, 32(5), 13. 

Colloidal form of transport of ferric iron in the Precambrian, apparently, was less important than in later geologic epochs. On the basis of an examination of the known methods of formation of colloidal solutions, it can be assumed that condensation phenomena predominate in the geochemical processes, and dispersion and peptization play a secondary role. Consequently one of the conditions for obtaining colloidal solutions is the presence of ionic solutions as an obligatory intermediate stage in the cycle weathering transport deposition. 

As a result, a physicochemical model for the formation of the BIF is proposed which is consistent with modern ideas on the evolution of sedimentation and volcanism and of the atmosphere, hydrosphere, and biosphere in the Precambrian. This model, which proposes a mainly volcanic source for the iron and silica and a biochemical and chemical mechanism of deposition, is the most likely but not the only possible one. Other versions, or different interpretations, are not ruled out, but it is perfectly obvious that in any genetic postulates, the specific physicochemical data must be taken into account. It is also quite understandable that in a work which is a first attempt at physicochemical analysis of the entire geological cycle— source of the material transport deposition diagenesis metamorphism—not all the problems have been worked out in sufficient detail and not all the evidence is conclusive far from it. Further investigations in this direction are needed, including not only determination of the role of the individual parameters in ore formation, but also direct experimental modeling of the process. 

Beard, D.L., Johnson, C.M., Von Damm, K.L. and Poulson, R.L., 2003. Iron isotope constraints on Fe cycling and mass balance in oxygenated Earth oceans. Geology, 31 629-632. 

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