Oxides oxyhydroxide

Powell AK (1997) Polyiron Oxides, Oxyhydroxides and Hydroxides as Models for Biomineralisation Processes. 88 1-38... 

The hydroxyl (OH) group is the dominant reactive functional group on the surface of many solid phase particles, amorphous silicate minerals, metal oxides, oxyhydroxides, and hydroxides [17,25,160]. In the case of various organic pol-... 

Next we explore using the 5 Fe value of the ferric oxide/oxyhydroxide precipitate as a proxy for 5pe(ni)aq, which allows Equation (21) to be used to calculate the Ape(ni)-Fe(n) fractionation from the measured 5 Fe values for the ferric precipitate and Fe(II)aq. This approach is valid when the molar proportion of Fe(III)3q is very small. However, if there is a significant Fe isotope fractionation between Fe(III)3q and ferric hydroxide precipitate, this must be taken into account. As discussed in the previous chapter (Chapter 10A Beard and Johnson 2004), at low... 

Figure 17. Predicted Fe isotope variations produced by redox cycling of Fe due to APIO and DIR by bacteria, as envisioned from Fig. 16. The initial 6 Fe of the pool, as well as that of the influx of Fe(II), [JF n).Exi] is assumed to be zero. Solid lines show the 6 Fe values for ferric oxide/oxyhydroxide deposits as a function of solidification of the pool as an iron deposit is formed, and dashed lines show the 6 Fe values for Fe(II),. Depending upon the relative fluxes of external Fe(II), [Tpem-Ext], return of Fe(II) to the pool by DIR [Tpean Bio]. and precipitation of ferric oxide/oxyhydroxides by APIO [JF nnppd, a wide range of 6 Fe values can be produced.

Quartz Si02 FeMn oxides/ oxyhydroxides Nodules and crusts... 

Blesa, M.A. Maroto, A.J.G. (1986) Dissolution of metal oxides. J. chim. phys. 83 757—764 Blesa, M.A. Matijevic, E. (1989) Phase transformation of iron oxides, oxyhydroxides, and hydrous oxides in aqueous media. Adv. Colloid Interface Sci. 29 173-221 Blesa, M.A. Borghi, E.B. Maroto, A.J.G. Re-gazzoni, A.E. (1984) Adsorption of EDTA and iron-EDTA complexes on magnetite and the mechanism of dissolution of magnetite by EDTA. J. Colloid Interface Sci. 98 295-305 Blesa, M.A. Larotonda, R.M. Maroto, A.J.G. Regazzoni, A.E. (1982) Behaviour of cobalt(l 1) in aqueous suspensions of magnetite. Colloid Surf. 5 197-208... 

Peterson, M.L. Brown Jr., G.E. Parks, G.A. (1997) Quantitative determination of chromium valence in environmental samples using XAFS spectroscopy. In Voigt, J.A. Bunker, B.C. Casey,W.H. Wood,T.E. Crossey, L.J. (eds.) Aqueous chemistry and geochemistry of oxides, oxyhydroxides, and related materials. Materials Research Society, Pittsburgh... 

Oxides/Oxyhydroxides. For natural solids that are oxides or oxyhydroxides (e.g., quartz, Si02 goethite, a-FeOOH gibbsite, Al(OH)3), their water-wet surface is covered by hydroxyl groups (recall Fig. 11.2). These hydroxyl moieties can undergo proton-exchange reactions with the aqueous solution much like dissolved acids ... 

Oxides, Oxyhydroxides, and Short-Range Ordered Minerals 77... 

When considering results for AU/AI2O3 catalysts, it has to be remembered that the oxides, oxyhydroxides and hydroxides of aluminium can exist in many crystalline forms and can have a wide range of surface areas, these can both change in response to pretreatments, structure, surface area and changes during preparation are not always reported. There has been no systematic study of the importance of these variables on catalytic activity. 

Wetlands have the potential to remove metals from AD by metal adsorption on ferric oxyhydroxides, metal uptake by plant and algae, metal complexation by organic materials, and metal precipitation as oxides, oxyhydroxides, or sulfides. However, only metal precipitation as either oxides or sulfides has long-term metal-removal potential (Evangelou, 1995b). 

Nanoparticles and the Environmenf targets naturally occurring, finely particulate minerals, many of which form at low temperature. Thus, many of the compounds of interest are those of the clay fraction . Of course, there have been decades of critical work on the structures, microstructures, and reactivity of finely crystalline or amorphous minerals, especially oxides, oxyhydroxides, hydroxides, and clays. We will not summarize what is known in general about these (for this, the reader is referred to earlier Reviews in Mineralogy volumes). Rather, our goal is to focus on the features of these materials that stem directly or indirectly from their size. 

The dissolution reactions of oxides, oxyhydroxides and hydroxides of trivalent and divalent metals are of interest to soil and environmental scientists... 

When pore waters in both marine and continental sediments become significantly depleted in dissolved oxygen (< 0.5 ml/1), three geochemical subzones successively prevail (Fig. 1) (i) nitrate reduction into nitrogen (NR) (ii) manganese reduction to Mn aq. (MnR) and, subsequently, (iii) iron reduction to Fe " aq. (FeR). The type and elemental composition of carbonate cement formed are hence strongly controlled by the amount of Fe-and Mn-oxides/oxyhydroxides. 

To calculate the moles of metal oxides in manganese nodules only oxides/ oxyhydroxides of Mn and Fe as MnOj and FeOOH were taken into consideration. The amount of other oxides having oxidising capability such as oxides of Co, Cu and Ni are vary small. 

As iron oxides / oxyhydroxide have a very high affinity for the adsorption of anions as well as cations under natural conditions the early diagenetic reactivity of iron is often of great significance for the behavior of compounds such as trace metals, phosphate and organic acids. The adsorption on iron oxides is caused by the... 

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