Atmospheric water iron cycling

Behra, P., and L. Sigg (1990), "Evidence for Redox Cycling of Iron in Atmospheric Water", Nature 344, 419-421. 

Behra, P. and Sigg, L. (1990) Evidence for redox cycling of iron in atmospheric water droplets. Nature, 344, 419-421. 

Sedlak, D.L. and Hoigne, J. (1993) The role of copper and oxalate in the redox cycling of iron in atmospheric waters. Atmos. Environ., 27, 2173-2185. 

The iron cycle shown in Figure 12.11 illustrates some of the redox processes typically observed in soils, sediments, waters, and atmospheric water droplets, especially at oxic-anoxic boundaries. The cycle includes the reductive dissolution of iron(III) (hydr)oxides by organic ligands, which may also be photo-catalyzed in surface waters, and the oxidation of Fe(II) by oxygen, which is catalyzed by surfaces. The oxidation of Fe(II) to Fe(III) (hydr)oxides is accompanied by the binding of reactive compounds (heavy metals, phosphate, or organic compounds) to the surface, and the reduction of the ferric (hydr)oxides is accompanied by the release of these substances into the water column. 

Sedlak, D. L., and Hoign6, J. (1993) The Role of Copper and Oxalate in the Redox Cycling of Iron in Atmospheric Waters, Atmosph. Environ. 27A, 2173-2185. 

Basic oxygen furnaces (BOFs) have largely replaced open hearth furnaces for steelmaking. A water-cooled oxygen lance is used to blow high-purity oxygen into the molten metal bath. This causes violent agitation and rapid oxidation of the carbon, impurities, and some of the iron. The reaction is exothermic, and an entire heat cycle requires only 30-50 min. The atmospheric emissions from the BOF process are listed in Table 30-16. 

Iron objects which are exposed to the atmosphere or are partly immersed in water are often subjected to alternate cycles of wetting and drying (Pourbaix, 1974 Schwitter and Bdhni, 1980). These cycles may be due to seasonal fluctuations in weather conditions or be the result of tidal movements or of splashing. They cause the corro-... 

Faust, B. C., A Review of the Photochemical Redox Reactions of Iron(III) Species in Atmospheric, Oceanic, and Surface Waters Influences on Geochemical Cycles and Oxidant Formation, in Aquatic and Surface Photochemistry (G. Helz, R. Zepp, and D. Crosby, Eds.), Chap, f, pp. 3-37, Lewis, Boca Raton, FL, 1994b. 

Storage of sulfur in lake sediments results from cycling of S in the lake water and postdepositional diagenetic processes in sediments. The major features of S cycling in lakes are well known. Sulfur is a macronutrient uptake by phytoplankton and subsequent burial of organic S in sediments occur in all lakes (23, 62, 63). Putrefaction of organic S releases H2S (as well as trace amounts of other S gases 64-66) that is either fixed in sediments as iron sulfides, lost to the atmosphere via diffusion or ebullition, or oxidized. 

Faust BC (1994) A review of the photochemical redox reactions of iron(III) species in atmospheric, oceanic, and surface waters Influences on geochemical cycles and oxidant formation. In Aquatic and Surface Photochemistry. RG Zepp, DG Crosby, GR Helz (eds) p 3-37. Boca Raton, Florida Lewis Publishers... 

The disappearance of the BIFs at 1.7 billion years ago signaled the end of the previous state and the beginning of the third and final state of atmospheric oxygen evolution and, accordingly, evolution of Ocean chemistry. Once the deep ocean waters were cleared of ferrous iron, atmospheric O2 would rapidly have approached its present concentration. The carbon cycle would have been operating more or less as today. 

The spontaneity of this reaction is reflected in the AG value of — 125kJ/mol(C). The result is that the total equivalents of reduced matter produced by carbon burial are redistributed and now include some pyrite. Sulfate is removed from the water permeating the sediments and magnesium and calcium carbonates are formed. Thus, the carbon, oxygen, and sulfur cycles are coupled by a redox reaction which also includes iron. The extent of the coupling depends on the supplies of reactive organic carbon, sulfate, and reactive iron. When the reduced material is returned to contact with the atmosphere, it is oxidized and an amount of oxygen equivalent to that formed when the carbon was first buried is removed. 

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