Oxy-hydroxides

The reduction of molybdate salts in acidic solutions leads to the formation of the molybdenum blues (9). Reductants include dithionite, staimous ion, hydrazine, and ascorbate. The molybdenum blues are mixed-valence compounds where the blue color presumably arises from the intervalence Mo(V) — Mo(VI) electronic transition. These can be viewed as intermediate members of the class of mixed oxy hydroxides the end members of which are Mo(VI)02 and Mo(V)0(OH)2 [27845-91-6]. MoO and Mo(VI) solutions have been used as effective detectors of reductants because formation of the blue color can be monitored spectrophotometrically. The nonprotonic oxides of average oxidation state between V and VI are the molybdenum bronzes, known for their metallic luster and used in the formulation of bronze paints (see Paint). 

The results of development work on processes indicate that the two main methods of preventing the duplex microstructure from forming appear to be fast-firing, or increasing the amount of / "-alumina at low temperatures. Based on these results, Duncan et al. [20] and Zyl et al. [21] have described production processes starting from aluminum oxy-hydroxides or aluminum hydroxides as precursors for the synthesis of the solid electrolyte "-alumina. Duncan et al. described an alumina precursor which substitutes in part or wholly for or-alumina in an established... 

Approximately 80% of Zn production involves hydrometallurgy, in which roasted sulfide concentrates are dissolved in sulfuric acid.181 Currently, the major separation steps involve the precipitation of other metals from the sulfate stream (Figure 7) 181>182 The precipitation of iron is achieved by raising the pH with calcine, the mixture of zinc/iron oxides from roasting, producing large volumes of iron oxy-hydroxide materials, the disposal of which presents major challenges.183-185... 

Berrodier, I., Farges, F., Benedetti, M., Winterer, M., Brown Jr, G. E., Deveughele, M. (2004). Adsorption mechanisms of trivalent gold on iron- and aluminum-(oxy)hydroxides. Part 1 X-ray absorption and Raman scattering spectroscopic studies of Au(III) adsorbed on ferrihydrite, goethite, and boehmite. Geochimica et Cosmochimica Acta, 68(14), 3019-3042. doi 10.1016/j.gca.2004.02.009... 

Cances, B., Benedetti, M., Farges, F., Brown, G. E. (2007). Adsorption mechanisms of trivalent gold onto iron Oxy-Hydroxides From the molecular scale to the model. InB. Hedman P. Painetta (Eds.), 13th International Conference on X-Ray Absorption Fine Structure (XAFS13) (Vol. 882, pp. 217-219). Stanford, CA, USA. 

According to Mottl and McConachy (1990), amorphous silica (SiC>2) is the only silica polymorph present in the smoke at the site. To allow it to form in the calculation, we suppress each of the more stable silica polymorphs. We also suppress hematite (Fe203) in order to give the iron oxy-hydroxide goethite (FeOOH) a chance to form. 

These acidic waters are toxic to plant and animal life, including fish and aquatic insects. Streams affected by acid drainage may be rendered nearly lifeless, their stream beds coated with unsightly yellow and red precipitates of oxy-hydroxide minerals. In some cases, the heavy metals in acid drainage threaten water supplies and irrigation projects. 

As pH rises, the metal content of drainage water tends to decrease. Some metals precipitate directly from solution to form oxide, hydroxide, and oxy-hydroxide phases. Iron and aluminum are notable is this regard. They initially form colloidal and suspended phases known as hydrous ferric oxide (hfo, FeOOH n O) and hydrous aluminum oxide (HAO, AlOOH nH.2O), both of which are highly soluble under acidic conditions but nearly insoluble at near-neutral pH. 

Figure 11 shows the results of these experiments for the same pelleted Pt/Pd/Rh/Ce/A O catalyst used for the data in Figure 9. The oxygen content of the catalyst bed increased linearly with pulse duration and reached the steady-state lean level within 0.5 s. The oxygen capacity of the catalyst was associated primarily with oxidation of the 190 umol of Ce contained in each gram of catalyst the catalyst contained only 8 umol of precious metal per gram. A comparison of the oxygen capacity to the amount of Ce in the catalyst suggests that about 76% of the Ce could change between the +3 and +4 oxidation states (the most common oxidation states of Ce). The identities of the Ce compounds which undergo oxidation and reduction in exhaust are not known, however, dispersed hydroxides and oxy-hydroxides are likely candidates (18).

Belzile, N., Chen, Y.W., Wang, Z.J., 2001. Oxidation of antimony (III) by amorphous iron and manganese oxy hydroxides. Chemical Geology, 174, 379-389. 

Fig. 1 shows the cyclic voltammetry of an FePc/XC-72 dispersion, heated at 280°C in an inert atmosphere, in the form a thin porous Teflon bonded coating electrode in a 1 M NaOH solution. A description of the methodology involved in the preparation of this type of electrode may be found in Ref. 3. As can be clearly seen, the voltammetry of this specimen exhibits two sharply defined peaks separated by about 330 mV. The potentials associated with these features are essentially identical to those found by other workers for the reduction and oxidation of films of iron oxy-hydroxide formed on a number of host surfaces, including iron and carbon.(5)... 

Seredych M, Mabayoje 0, Bandosz TJ. Visible-light-enhanced Interactions of hydrogen sulfide with composites of zinc(oxy)hydroxide with graphite oxide and graphene, Langmuir 2012, 28, 1337-1346. 

Seredych M, Mabayoje 0, and Bandosz TJ. Role of water splitting in visible light enhanced reactive adsorption ofS02 on composites of Zinc(Oxy)Hydroxide with Graphite Oxide and Graphene, Adv. Funct. Mater., submitted... 

Thus the dissolved ferrous species would further react with the hydroxyl ions generated at the cathodic sulphide mineral sits forming iron oxy-hydroxide species ... 

The cathodic reaction is oxygen reduction in Eq. (1-1). Because Fe(OH)3 and metal oxy-hydroxide species of iron, lead and zinc formed will coat the cathodic mineral surface, affecting its floatability. 

Mo alloys of Pt have also been shown to enhance the CO tolerance of PEM fuel cell catalysts.Two peaks are often observed in the CO stripping volta-mmograms for PtMo catalysts the first at approximately 0.4 V vs RHE and the second at approximately 0.75 V. The first has been attributed to enhanced oxygen transfer from Mo oxy-hydroxide species on the surface of the catalyst particles. XANES at the Mo K and Pt L3 edges has provided support for the presence of such oxy-hydroxide species. Mukerjee et have shown that the... 

PtMo alloys are not as effective as PtRu for methanol, or ethanol, oxidation. As shown in Figure 29, the d band vacancy per Pt atom for the PtMo/C catalyst continues to increase until 0.6 V vs RHE, in contrast to the behavior of PtRu/C. ° The authors attribute this difference to the lack of removal of the Cl fragments from the particle surface by the oxy-hydroxides of Mo. However, the difference in the electrocatalytic activity of PtRu and PtMo catalysts may be attributed to ensemble effects as well as electronic effects. The former are not probed in the white line analysis presented by Mukerjee and co-workers. In the case of methanol oxidation, en-... 

Fortunately, ground waters dissolve and transport metals from mineral deposits at depth to the surface, where the metals adsorb onto the surfaces of organic matter and Fe- and Mn-oxy-hydroxide particles in the soil. Unfortunately, the adsorption of these ions contributes only a small amount of additional metal to the soil, resulting in marginally anomalous... 

Acebal, S.G. Mijovilovich, A. Rueda, E.H. Aguirre, M.E. Saragovi, C. (2000) Iron-oxide mineralogy of a mollisol from Argentina A study by selective-dissolution techniques, X-ray diffraction, and Mossbauer spectroscopy. Clays Clay Min. 48 322-330 Adams, W.A. Kassim, J.K. (1984) Iron oxy-hydroxides in soils developed from lower palaeozoic sedimentary rocks in mid-Wales and implications for some pedogenetic processes. J. Soil Sd. 35 117-126... 

P.G. Triay, I.R. Hobart, D.E. Meijer, A. (1992) EXAFS spectroscopic study of neptu-nium(V) sorption at the a-FeOOH/water interface. Environ. Sci. Technol. 26 376-382 Combes, J.M. Manceau, A. Galas, G. (1986) Study of the local structure in poorly ordered precursors of iron oxi-hydroxides. J. Physique 47 697-701... 

Herbert Jr, R.B. (1995) Precipitation of Fe oxy-hydroxides and jarosite from acidic ground-water. GFF 117 81-85... 

Mossbauer characterization of iron oxides and (oxy)hydroxides the present state of the art. Hyperfme Interactions 126 247-259... 

The hydroxide so formed will react with the metal ion to form the metal hydroxide, hydrated oxide, or oxide, depending on the relative stability of the various oxides and hydroxides. (The resulting hydroxides or oxy hydroxides can be heated in air or oxygen to form the oxides.) In addition, insoluble carbonates may also form. The competition between hydroxide and carbonate will depend on their solubility products. Carbonates tend to be more solnble than hydroxides of the same metal ion. On the other hand, the valne of K for equilibrium (3.32) (1.8 X 10 " ) means that the concentration of hydroxide will be ca. four orders of magnitude less than that of carbonate (assnming no other pH-determining species is present). 

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