Oxidation fractional

Ammonium chloride is used as a flux ia the melting furnace because the large surface of the cathodes favors the formation of dross, ie, oxide-coated globules of ziac. The dross is separated by Hquation or air-swept milling iato metal and oxide fractions. In the latter, the oxide fraction is swept out of the mill and can be returned to roasting for the elimination of chloride. Metallic ziac is recycled. Overall melting efficiency is 96—98%. 

In this work a novel five-step leaching scheme for HM has been developed addressing exchangeable, acid soluble (carbonate), easily reducible (bound to Mn oxides), easily oxidizable (bound to humic and fulvic acids), and moderately reducible (bound to amorphous Ee oxides) fractions extractable by 0.05 M Ca(N03), 0.43 M CH3COOH, 0.1 M NH,OH-HCl (non-acidified), 0.1 M K/,03 (pH 11), and 0.1 M (NH4),C,04 (pH 3), respectively. The sequence of extractants was chosen according to recent studies on the selectivity of leachants toward dissolved phases of soils. 

Figure 5.3. Effects of soil pH on the Zn amount bound to the Fe oxide fraction (amorphous/crystalline Fe oxide and overall Fe oxide bound fractions) in soils from China with pH 3.73-8.1 and 0-14.7% CaC03 (after Han et al., 1995. Reprinted from Geoderma, 66, Han F.X., Hu A.T., Qi H.Y., Transformation and distribution of forms of zinc in acid, neutral and calcareous soils of China, p 128, Copyright (1995), with permission from Elsevier)...

Manganese in uncontaminated Israeli arid soils is predominantly in the easily reducible oxide fraction (35-40% of the total-HN03 Mn), followed by the carbonate fraction (18-25%), and the residual fraction (14-25%) (Han and Banin, 1996) (Table 5.4). Manganese in the organic fraction amounts to 9-12% and in the reducible oxide fraction to 5-11%. The exchangeable fraction of Mn in the soils is very low. In the sludge-amended calcareous soils of Southeast Spain, the residual and the carbonate bound Mn fractions are the major solid-phase (Moral et al., 2005). In comparison, the Mn in fine-textured soils from the southeastern United States is... 

The data for the six Israeli arid soils show that Co contents in the easily reducible oxide, the organic matter, the reducible oxide and the residual fractions and the total Co are linearly related to the Mn contents in each respective fraction. Correlation coefficients between the respective Co and Mn fractions are significant at the 5% probability level (Fig. 5.6). The Co/Mn molar ratios are 0.0186, 0.0177, 0.0075, 0.0205, 0.0364 in the total, the easily reducible oxide, the organic matter, the reducible oxide and the residual fractions, respectively. Therefore, Co is more preferentially incorporated in the reducible oxide (Fe oxide) fraction than Mn. Much of the Co in arid soils is included in the easily reducible oxide (Mn oxide) fraction,... 

Co2+ to Co3+, but also from a direct exchange of Co2+ for Mn2+ produced during the redox reaction. The cobalt in arid soils, as indicated by Han et al. (2002b), mainly occurs in the residual and the Mn oxide (easily reducible oxide) fractions. Furthermore, after water saturation, the Co is transferred mainly from the Mn oxide fraction into the carbonate and exchangeable fraction. This will be discussed in detail in the next chapter. 

The bioavailability of trace elements in soil-water-plant ecosystems of arid zones is largely determined by their partitioning between solution and solid-phase components. The redistribution and transformation of trace elements among solid-phase components under various biogeochemical conditions strongly adjust their lability and bioavailability. Soluble, exchangeable and organically bound forms are bioavailable to plants. The carbonate bound fraction represents a reservoir of potentially bio-available trace elements to plants. In paddy soils, the amorphous Fe/Al oxide fraction contributes to trace element availability as well. 

Banin et al. (1990) reported that most of the Pb in Israeli sewage sludge was bound in the reducible oxide fraction (46%), followed by the readily reducible oxide (20%) and the carbonate (18.7%) fractions. McGrath and Cegarra (1992) found that Pb mainly existed in the residual and the carbonate fractions. 

Shuman L.M., Separating soil iron- and manganese-oxide fractions for microelement analysis, Soil Sci Soc Am J 1982 46 1099-1102. 

In Limnodrilus sp., an oligochaete worm, copper bioavailability from surhcial freshwater sediments is associated with the amount of copper present in the manganese oxide fraction of the sediment. The redox potential and pH in the gut of Limnodrilus allows the dissolution of the manganese oxide coating, making copper and other metals available for uptake (Diks and Allen 1983). 

An interesting consequence of the highly nonuniform electrostatic potential and distribution of the molecular species is that the local activity coefficients of the chemical species taking part in chemical equilibria depend on their exact location at the interface. As an example, Figure 2.8 shows that the oxidation fraction of the osmium sites is a nonuniform function of the distance to the electrode. The consequences of this finding for the electrochemical response will be discussed in Section 2.3.4. 

Similarly, in 1843, Mosander separated from the original yttria three oxide fractions, one white, one yellow (old erbia) and one rose colored (old terbia), (Shown in Figure 2)... 

In addition to a better understanding of the reaction of sulfide with ferric oxides and its role in pyrite formation, a more exact definition of the term reactive iron is critical. Does reactive iron mean a different iron oxide fraction for bacterial dissolution (e.g., weathering products such as goethite or hematite) than for reaction with sulfide (e.g., reoxidized lepidocrocite) In other words, is there a predigestion of ferric oxides by bacteria that allows a subsequent rapid interaction of sulfide with ferric oxides ... 

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