Oxides of Fe, Al, and

Such reactions can occur on oxides of Fe, Al, and Ti. Carboxylic acids and phenols are common reactive moieties of the sorbates /. Often the resultant bound species is not really known. Given this additional sorption mechanism, the situation becomes more complicated, and multiple equilibria must be modeled (Stone et al. 1993) to account for all species ... 

Oxides of Fe, Al, and Mn commonly occur in soils, particularly those in advanced stages of weathering (Hsu, 1989 Cornell and Schwertmann, 1996 Kampf et al., 2000 Churchman, 2000 Violante et al., 2002c). 

Molybdenite concentrate contains about 90% M0S2. The remainder is primarily siUca, with lesser amounts of Fe, Al, and Cu. The concentrate is roasted to convert the sulfide to technical molybdic oxide. Molybdenum is added to steel in the form of this oxide. In modem molybdenum conversion plants, the oxidized sulfur formed by roasting M0S2 is converted to sulfuric acid. 

If sediment was collected from a particular waterway, the distribution of the element of interest between different components of the sediment was found to vary with the degree of exposure to air and the temperature of any drying stages (Rapin et al., 1986 Kersten and Foerstner, 1986). The minor elements present in sediments (and soils) are not uniformly distributed. Part can be present as mineral fragments derived from the original parent rock, while other parts can be associated with distinct component phases such as carbonate compounds, hydrous oxides of Fe, Al, Mn and organic matter. Some fractions are loosely sorbed on particle surfaces or are held on ion exchange sites. 

Kurimura et al. (22) studied the oxidation of Fe +(EDTA) and Fe +(NTA) by dissolved oxygen in aqueous solutions and suggested that the oxidation proceeds by two parallel reaction paths, with both pro-tonated and unprotonated chelates reacting. The reaction mechanisms suggested (22,23) are as follows ... 

Hydrophilic, 17 Hydrophobic, 17 Hydroquinone, 134, 253 Hydroxides of Fe, Al, and Mn, 131 See Iron oxides Aluminum oxides ... 

Figure 11.6. Oxidation of Fe(II) and Mn(II) by oxygen. All experiments were conducted with dissolved Fe(II) or Mn(II) concentrations of less than 5 x 10 M. In each series of experiments, the pH was controlled by continuously bubbling CO2- and O2-containing gas mixtures through HCOJ solutions of known alkalinity, (a) Oxygenation of Fe(II) in bicarbonate solutions, (b) Removal of Mn(II) by oxygenation in bicarbonate solutions, (c) Oxidation of Mn(II) in HCOs solutions autocatalytic plot, (d) Effect of pH on oxygenation rates, (e) Oxidation rate of ferrous iron as a function of pH. At low pH the oxidation rate is independent of pH, while in the higher pH range equation 13 (second-order dependence on [OH ]) is fulfilled. (From Singer and Stumm, 1970. More recent data by Millero et al., 1987.)...

Desorption on Metal Reduction Many bacteria and archaea can respire on Mn(lll/tV) and Fe(lll) oxides, leading to their dissolution, with the potential for concomitant displacement of arsenic into the aqueous phase (Cummings et al., 1999). In fact, within most soils and sediments, total As levels correlate with Fe content rather than Al or clay content (Smedley and Kinniburgh, 2002), and thus reductive dissolution—transformation of Fe(lll) phases should have a major impact on arsenic. Respiratory reduction of Fe in sediments generally occurs in zones where O2, NOs , and Mn(lV) [all being oxidants of Fe(ll) and alternative electron acceptors] are diminished (Lovley, 2000). 

Noncrystalline aluminosilicates (allophanes), oxides, and hydroxides of Fe, Al, and Mn, and even the edges of layer silicate clays to a lesser extent, provide surface sites for the chemisorption of transition and heavy metals. All of these minerals present a similar type of adsorptive site to the soil solution a valence-unsatisfied OH or H2O ligand bound to a metal ion (usually Fe ", AF, or Mn ). For example, on iron oxides, a trace metal, M, may bind according to the reaction... 

As with metal cations, anion chemisorption occurs on soil minerals that possess surface hydroxyl groups. The most important minerals in this regard are noncrystalline aluminosilicates (allophanes) oxides and hydroxides of Fe, Al, and Mn and layer silicate clays (edge sites only). It is the H2O or valence-unsatisfied OH ligands bound to surface metal ions (usually Fe, Al, or Mn) that are the sites of chemisorption. In general terms, the surface reaction can be written... 

Copper occurs in soil solids and solutions almost exclusively as the divalent cation Cu ". However, reduction of Cu " (cupric) to Cu (cuprous) and Cu (metallic copper) is possible under reducing conditions, especially if halide or sulfide ions ( soft bases) are present to stabilize Cu" (a soft acid). Copper is classified as a chalcophile, owing to its tendency to associate with sulfide in the very insoluble minerals, CU2S and CuS. In reduced soils, then, copper has very low mobility. Most of the colloidal material of soils (oxides of Mn, Al, and Fe, silicate clays, and humus) adsorb strongly, and increasingly so as the pH is raised. For soils with high Cu accumula-... 

Because Mo is weakly adsorbed on soils and hydrous oxides of Fe (Karimian and Cox, 1979) at alkaline pH, these soils have a relatively large proportion of Mo in the solution phase (Reisenauer et al., 1962). 

In some cases, the oxidation products of the particle itself may provide some protection. For example, the accumulation of oxides on the surfece of Fe, Al and Ti particles probably act to slow their air oxidation. 

The loss of easily soluble potassium from the trioctahedral mica biotite will be compensated for by ion exchange with H3O ions, by oxidation of Fe ions, and by the replacement of Al in the octahedral layer by Si. On the other hand, the dioctahedral mica muscovite (Figure 2.6) undergoes similar potassium loss by degradation and associated charge deficiency (Table 2.3). In the resulting dioctahedral illites, the ideal Si/Al ratio of 3 in the tetrahedral layer of muscovite is changed to between 5 and 40 (Hower and Mowatt, 1966). In addition, water is intercalated between the layer stacks. 

In the double-neutralization process, Na2SiFg is precipitated and removed by filtration at a pH of 3—4 (9). Upon raising the pH to 7—9, insoluble phosphates of Fe, Al, Ca, and Mg form and separate. Iron can be precipitated as hydrous ferric oxide, reducing the phosphate loss at the second filter cake. Both the fluorosihcate and metal phosphate filter residues tend to be voluminous cakes that shrink when dewatered recovery of soluble phosphates trapped within the cakes is difficult. 

The physicochemical properties of carbon are highly dependent on its surface structure and chemical composition [66—68], The type and content of surface species, particle shape and size, pore-size distribution, BET surface area and pore-opening are of critical importance in the use of carbons as anode material. These properties have a major influence on (9IR, reversible capacity <2R, and the rate capability and safety of the battery. The surface chemical composition depends on the raw materials (carbon precursors), the production process, and the history of the carbon. Surface groups containing H, O, S, N, P, halogens, and other elements have been identified on carbon blacks [66, 67]. There is also ash on the surface of carbon and this typically contains Ca, Si, Fe, Al, and V. Ash and acidic oxides enhance the adsorption of the more polar compounds and electrolytes [66]. 

Phosphorus (P) is one of the major limiting factors for plant growth in many soils. Plant availability of inorganic phosphorus (Pi) can be limited by formation of sparingly soluble Ca phosphates, particularly in alkaline and calcareous soils by adsorption to Fe- and Al-oxide surfaces in acid soils and by formation of Fe/ Al-P complexes with humic acids (94). Phosphorus deficiency can significantly alter the composition of root exudates in a way that is, at least in some plant species, related to an increased ability for mobilization of sparingly soluble P sources (29,31,71). 

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