Oxidation and Fe

Acrylate and low-molecular-weight acrylic acids are effective slime depressants/disper-sants. Suspendol PKK and PC improved separation efficiency between zinc and iron oxides. Starches, mainly hydrolysed starch and cooked starch, are effective depressants in the treatment of oxidized zinc ores that contain iron oxides and Fe-hydroxides. 

Chemolithoautotrophic Hydrogen-Oxidizing and Fe(III)-Reducing Strains Related to the Glucolytic Species... 

These oxidation states attract attention because Fe(IV) and Fe(V) cation radical porphyrins are active intermediates in biological hydroxylation. In strong base, Fe(IV) is produced from Fe(III) by powerful oxidants and Fe(V) arises from radical reduction of Fe(VI)... 

The calculations in Section 6.2 indicate that the root system as a whole can sustain considerable rates of O2 loss to the rhizosphere without compromising their internal O2 requirements. The standard O2 flux in the calculations in Section 6.2 was 0.5 nmol dm (root) s for the parts releasing O2. For rice roots grown in soil, Begg etal. (1994) obtained values of 0.1-1.2nmol dm (root) s from rates of Fe + oxidation and Fe(III) accumulation near planar layers of rice roots in anaerobic soil, and Kirk and Bajita (1995) obtained 0.1-0.2 nmol dm (root) s with the same experimental system but a soil with a smaller ferrous iron content. These values probably underestimate the total O2 release because they did not allow for O2 consumed by soil microbes. Revsbech et al. (1999) obtained values of 1-3 nmol dm (root) s from measurements of O2 gradients made with a microelectrode near rice roots in the soil used by Kirk and Bajita (1995). These values are in the middle of the range described above. 

A heterogeneous natural system such as the subsurface contains a variety of solid surfaces and dissolved constituents that can catalyze transformation reactions of contaminants. In addition to catalytically induced oxidation of synthetic organic pollutants, which are enhanced mainly by the presence of clay minerals, transformation of metals and metalloids occurs with the presence of catalysts such as Mn-oxides and Fe-containing minerals. These species can alter transformation pathways and rates through phase partitioning and acid-base and metal catalysis. 

Baker JA, Macpherson CG, Menzies MA, Thirlwall ME, Al-Kadasi M, Mattey DP (2000) Resolving cmstal and mantle contributions to continental flood volcanism, Yemen consfrainfs from mineral oxygen isofope data. J Petrol 41 1805-1820 Bald N, BuUen TD, Witte-Lien K, Shanks WC, Motelica M, Mandernack KW (2006) Iron isotope fractionation during microbiaUy simulated Fe(II) oxidation and Fe(III) precipitation. Geochim Cosmochim Acta 70 622-639... 

Rate constants for many [Fe(CN)6] oxidations and [Fe(CN)g] reductions have been collected and tabulated. ... 

In relation to enzymic cytochrome P-450 oxidations, catalysis by iron porphyrins has inspired many recent studies.659 663 The use of C6F5IO as oxidant and Fe(TDCPP)Cl as catalyst has resulted in a major improvement in both the yields and the turnover numbers of the epoxidation of alkenes. 59 The Michaelis-Menten kinetic rate, the higher reactivity of alkyl-substituted alkenes compared to that of aryl-substituted alkenes, and the strong inhibition by norbornene in competitive epoxidations suggested that the mechanism shown in Scheme 13 is heterolytic and presumably involves the reversible formation of a four-mernbered Fev-oxametallacyclobutane intermediate.660 Picket-fence porphyrin (TPiVPP)FeCl-imidazole, 02 and [H2+colloidal Pt supported on polyvinylpyrrolidone)] act as an artificial P-450 system in the epoxidation of alkenes.663... 

Trace Metal Adsorption to Mixtures of Biogenic Mn Oxides and Fe Oxides... 

TRACE METAL ADSORPTION TO MIXTURES OF BIOGENIC Mn OXIDES AND Fe OXIDES... 

KINETIC MODELING UNPROMOTED PC OXIDATION AND Fe-ASSISTED PC OXIDATION OF PHENOL... 

Meunier has developed model chemistry for peroxidases such as ligninase with KHSO5 as oxo-transfer oxidant and Fe or Mn-tetrasulfoporphyrin in aq. MeCN. These catalysts oxidize lignin models such as veratryl alcohol (3,4-methoxybenzyl alcohol) to give biologically relevant products such as quinones. 

Weiss J. V., Emerson D. E., Backer S. M., and Megonigal J. P. (2(X)3) Enumeration of Fe(II)-oxidizing and Fe(III)-reducing bacteria in the root zone of wetland plants implications for a rhizosphere iron cycle. Biogeochemistry 64, 77-96. 

In stagnant surface waters, sediment-water, and soil systems, pe and pH are especially important master variables that are coupled to one another. An increase in pe is accompanied by a decrease in pH. Solid organic matter as well as heterogeneous redox couples involving the solid phases Mn(III,IV)oxides, Fe(II,III)oxides, and FeS and FeS2 in soils, sediments, and groundwaters provide important pe and pH buffering. 

Table 11.7. Laboratory Studies of Nonphotochemical Reduction of Mn(in,rV)(hydr)oxides and Fe(II,III)(hydr)oxides by Organics...

Figure 4 shows that activities of several kinds of iron oxide based catalysts. A Fe/Ca/Al oxides catalyst exhibited the best performance among the catalysts tested. Fe/Ca/Al and Fe/Al oxides catalysts were highly active, whereas Fe/Ca and Ca/Al oxides catalyst were extremely low in activity. The selectivities of Fe/Al oxides and Fe/Ca/Al oxides catalysts were almost the same (97% at 5.25 h), and the main by-products were benzene and toluene. Therefore the addition of an optimum amount of CaO to Fe/Al based catalyst could suppress the deactivation of the catalyst during long term reaction. Further experiment are under achievement to elucidate precisely the role of CaO. 

Second, the combined presence of and Mn in groundwater, and precipitation of both Mn-oxides and Fe-oxides would lead to separation in space of the precipitates, with reducing the Mn-oxides (Postma and Appelo, 2000). This may have special, but as yet not quantified effects on the behavior of As. 

A reduction in system pH enhances the solubility of PR, making the precipitation of pyromorphite minerals possible. However, the sorption of Pb decreases sharply as the system pH decreased, producing a sigmoidal function, usually referred to as an adsorption edge, which reflects the affinity of a metal species for a mineral surface (Sposito, 1984). The ability of Pb to form inner-sphere surface complexes is related to the ability of a species in solution to form hydroxides. In fact, it has been shown that surface affinity of metal cations for Fe-oxide and Fe-hydroxide surfaces agrees with their hydrolysis values (Hayes and Katz, 1996). An analogy between solution complexation and surface complexation is represented in the following reactions (Hayes and Katz, 1996) ... 

The extent of PHP adsorption is too low to be measured by loss from bulk solution. The catalysis of PHP hydrolysis by various metal oxides must come from their ability to chelate the ester and polarize the carbonyl C-O bond. Apparently Ti oxides and Fe oxides are capable of doing this, while Al oxides are not. Ionic strength effects on PHP surface-catalyzed hydrolysis are small electrostatics apparently have a minor role in ester chelation and subsequent attack by OH (Torrents and Stone, 1991). 

Water soluble peroxides and persulfates, in combination with a reducing agent such as ferrous (Fe ) and thiosulfate (8203 ) ions, are a common source of radicals in aqueous and emulsion systems. An example of such a redox system has hydrogen peroxide as the oxidant and Fe as the reductant ... 

Another redox system commonly used consists of persulfate as the oxidant and Fe " or 8203 as the reductant (Rudin, 1982 Odian, 1991) ... 

By this reaction, a single electron is transferred from each Fe " ion to the molecule. The ferrous iron is thereby oxidized to ferric iron, whereas the oxygen is reduced to water. In the geochemical literature, in such a reaction is termed the oxidant and Fe " the reductant. In the biological literature, the terms electron acceptor for and electron donor for Fe + are used. 

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