Fe and Mn oxides

Table 5.2. Percentages of trace metals bound in the Mn and Fe oxides in two Israeli arid soils treated with metal nitrates3...

Cobalt is capable of substitution for Fe2+ and other transition metals in the phyllosilicates due to the similarity of ionic radii. On the other hand, cobalt (Co2+) is specifically adsorbed by Mn and Fe oxides, and concentrations of Co sorbed by Mn oxides are much greater than those by Fe oxides (Backes, et al., 1995). Traina and Donor (1985) suggested that the Mn release during Co2+ ion sorption resulted not only from the oxidation of... 

Formation of the shallow-water concretions is associated with anoxic conditions that range in duration from seasonal to nearly continuous. For example, in the Baltic Sea, nodules and crusts are mostly found around the margins of the deep anoxic basins. They form from Mn and Fe that accumulates from the reduction of Mn and Fe oxides in the anoxic deep waters. When the basin is periodically flushed with oxic water from the North Sea, about once a decade, the concretions undergo growth as the fresh supply of metals is oxidized. 

Manceau, A. Combes, J.M. (1988) Structure of Mn and Fe oxides and oxyhydroxides a topological approach by EXAFS. Phys. Chem. Min. 15 283-295... 

Down-core porewater profiles of Mn2+, Fe2+, and H2S in sediments from Aarhus Bay estuary (Denmark) show sharp gradients in the subsurface peaks of Mn2+ and Fe2+, indicating the reduction of Mn and Fe oxides in the upper 2 and 4 cm, respectively... 

Specifically adsorbed Carbonates-bound Mn and Fe oxides-bound (Easily reducible) Mn-oxides-bound... 

In natural environments, Mn and Fe oxides often coexist as mixtures, making it important to determine if their trace metal adsorption properties are altered by interactions with each other. To test this hypothesis we measured Pb adsorption to mixtures of biogenic Mn oxide and colloidal Fe oxide. The mixtures were prepared in two ways. First, previously prepared biogenic Mn oxide was mixed in suspension with previously precipitated amorphous Fe(III) oxide. Second, Mn(II) was biologically oxidized in the presence of a previously prepared Fe(III) oxide suspension (Nelson et al., 2002). As above, all adsorption measurements were made in a chemically defined medium (Nelson et al., 1999b). In both cases, observed Pb adsorption by the Fe/Mn oxide mixtures was similar to that predicted using Langmuir... 

One method used adsorption to laboratory surrogate materials in an adsorption additivity model to estimate the relative contributions of Mn and Fe oxides and organic materials to Pb adsorption to natural biohlms. The second method made use of a novel selective extraction approach in which trace metal adsorption to surface coatings was measured before and after the selective removal of constituents. 

Dong, D. et al., Adsorption of Pb and Cd onto metal oxides and organic material in natural surface coatings as determined by selective extractions New evidence for the importance of Mn and Fe oxides, Water Res., 34, 427, 2000. 

Pb removal was controlled by a dual process of adsorption onto sinking particles and removal at the sediment-water interface, possibly onto highly active surfaces such as Mn and Fe oxides. This latter process was suggested to account for > 90% of the observed removal. 

In these examples as well as for most aquatic sediments, the principal diagenetic reactions that occur in these sediments are aerobic respiration and the reduction of Mn and Fe oxides. Under the slower sedimentation conditions in natural lakes and estuaries, there is sufficient time (years) for particulate organic matter to decompose and create a diagenetic environment where metal oxides may not be stable. When faster sedimentation prevails, such as in reservoirs, there is less time (months) for bacteria to perform their metabohc functions due to the fact that the organisms do not occupy a sediment layer for any length of time before a new sediment is added (Callender, 2000). Also, sedimentary organic matter in reservoir sediments is considerably more recalcitrant than that in natural lacustrine and estuarine sediments as reservoirs receive more terrestrial organic matter (Callender, 2000). 

Rock varnish Clay minerals, Mn and Fe oxides, and minor and trace elements colour ranges from orange to black due to variable concentrations of different... 

The significant role of hydrous Mn and Fe oxides. Adv. Chem. Ser. 73 337-387. Kolthoff, I.M. 1921. lodometric studies. VII. Reactions between arsenic trioxide and iodine. 

O Reilly. S.E. and Hochella, M.R, Lead sorption efficiencies of natural and synthetic Mn and Fe-oxides, Geochim. Cosmochim. Acta, 67,4471, 2003. 

An increase in carbonate alkalinity in the NR subzone enhances the precipitation of carbonate cements with 6 0 compositions similar to oxic carbonates, but with a slight enrichment in Mn and Fe and depletion in C. Rhodochrosite and siderite precipitate in the MnR and FeR subzones of sediments containing large amounts of Mn- and Fe-oxides, respectively. Because the three subzones overlap, it is common to observe, such as in deep-sea sediments, that suboxic siderites and rhodochrosite are enriched in Mn and Fe, respec-... 

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