Iron pentavalent

In REACT, we prepare the calculation by disenabling the redox couple between trivalent and pentavalent arsenic (arsenite and arsenate, respectively). As well, we disenable the couples for ferric iron and cupric copper, since we will not consider either ferrous or cupric species. We load dataset FeOH+.dat , which contains the reactions from the Dzombak and Morel (1990) surface complexation model, including those for which binding constants have only been estimated. The procedure is... 

Effects of Pentavalent Sb Ions on the Adsorption of Divalent Co-57 on Hematite. Benjamin and Bloom reported that arsenate ions enhance the adsorption of cobaltous ions on amorphous iron oxyhydroxide (J 6). Similarly, when divalent Co-57 ions were adsorbed on hematite together with pentavalent Sb ions, an increase of adsorption in the weakly acidic region was observed. For example, when 30 mg of hematite was shaken with 10 cm3 of 0.1 mol/dm3 KC1 solution at pH 5.5 containing carrier-free Co-57 and about 1 mg of pentavalent Sb ions, 95 % of Co-57 and about 30 % of Sb ions were adsorbed. The emission spectra of the divalent Co-57.ions adsorbed under these conditions are shown in Figure 8 together with the results obtained under different conditions. As seen in Figure 8, the spectra of divalent Co-57 co-adsorbed with pentavalent Sb ions are much different from those of Co-57 adsorbed alone (Figure 3). These observations show a marked effect of the.co-adsorbed pentavalent Sb ions on the chemical structure of adsorbed Co-57. 

In the met-Hr structure the two iron atoms differ in coordination number. Fe2 is pentacoordinate, yet has bond angles typical of octahedral iron with an open coordination site. This is in distinction to the pentavalent mononuclear iron proteins, which are better described as... 

A formally pentavalent cationic silicenium complex, with intramolecular base-stabilization, is the silylene-iron 167, with a Fe=Si double bond. The crystal structure of 167 shows that silicon is essentially tetrahedral in this compound, and the solution 29 Si chemical shift is 8 = 118.3 ppm, compatible with the double bond character rather than with pentacoordination at silicon189. 

Aqueous pentavalent vanadium is readily reduced to the tetravalent state by iron powder or by S02 gas. A stronger reducing agent, eg, zinc amalgam, is needed to yield divalent vanadium. Divalent and tfivalent vanadium compounds are reducing agents and require storage under an inert atmosphere to avoid oxidation by air. 

For vanadium solvent extraction, iron powder can be added to reduce pentavalent vanadium to quadrivalent and trivalent iron to divalent at a redox potential of —150 mV. The pH is adjusted to 2 by addition of NH3, and an oxyvanadium cation is extracted in four countercurrent stages of mixer— settlers by a diesel oil solution of EHPA. Vanadium is stripped from the organic solvent with a 15 wt % sulfuric acid solution in four countercurrent stages. Addition of NH3, steam, and sodium chlorate to the strip liquor results in the precipitation of vanadium oxides, which are filtered, dried, fused, and flaked (22). Vanadium can also be extracted from oxidized uranium raffinate by solvent extraction with a tertiary amine, and ammonium metavanadate is produced from the soda-ash strip liquor. Fused and flaked pentoxide is made from the ammonium metavanadate (23). 

Titanium is the only member of its family forming +3 compounds of appreciable stability (Zr, Hf, and Th are almost exclusively tetravalent). In group Va, only vanadium assumes a +4 oxidation state (its congeners almost invariably are pentavalent). In Group VIII, osmium and ruthenium can assume a valence of + 8, but their lighter congener, iron, apparently does not. 

Various porphyrin compounds such as NFevOEP are known.62 The i Fe=N) stretching frequency of 853 cm-1 is lower than that of the Cr and Mn analogues the nitrido Fev complex is stable only at very low temperature ( 30 K). It is widely accepted that one of the intermediate species in the catalytic cycle of cytochrome P-450 (see later) contains pentavalent iron. The reduction of an R3CFev moiety is an accepted part of the mechanism of dismutation of hydrogen peroxide to water and oxygen catalyzed by catalase. 

Ferromanganese nodules and seamount crusts are characterized by distinct alternating layers of iron oxides and manganese oxides in addition to other components such as aluminosilicates (shale), CFA, and sometimes biogenic barite and carbonates in seamount crusts. Iron-oxide phases are enriched in elements that exist in normal seawater mainly as hydroxyl and carbonate complexes of tri- to pentavalent cations (e.g.. As, B, Bi, In, Ir, Rh, REEs, Y, Ti, Th, U, Zr, Hf, Nb, and Ta), oxyanions (e.g., P, Re, Ru, Os, S, Se, Te, V, and W), and divalent cations... 

Distribution coefficients for uranium and other metals in tnoctylamine are con ared in Table 5.20. Although the conditions are not exactiy those used in the Amex process, they indicate that the only element normally present in leach liquors that extracts readily with uranium is mdybdenum. Ferric iron, whidi is always present in leach liquors and extracts in the Dapex prrocess, is not extracted in the Amex process. Vaiudium, if pentavalent, can be extracted by raising the pH from 1 to 2. 

Most of investigators postulate the pentavalent iron oxene complex, P450-Fe =0, as the direct oxidant of a substrate by analogy with the reactive intermediates of the catalytic cycle of peroxidase, which have the oxoferryl group, Fe =0, in their active center. However, the Mossbauer and Raman spec-... 

The oxyacids of pentavalent phosphorus are surprisingly numerous, and their chemistry is very complex. These considerations have only begun to be appreciated in recent years, when research has been stimulated by the discovery of important applications for the salts of these acids. The main application of the soluble phosphates is in water conditioning. Many of them possess the property of combining with calcium and magne- sium ions to form extremely stable soluble complexes that do not give precipitates with soap and do not deposit scale in boilers. Similar complexes are formed with iron, and stable soluble phosphates of iron find application in nutrition. Other uses for soluble phosphates are found in the textile industry, paints, and insecticide sprays. 

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