Formation of iron oxyhydroxide

Shah Singh, S. Kodama, H. (1994) Effect of the presence of aluminum ions in iron solutions on the formation of iron oxyhydroxides (FeOOH) at room temperature under acidic environment. Clays Clay Min. 42 606—613... 

It is well established that oxides of Fe and perhaps Mn and Al effectively adsorb or occlude most toxic metals. These oxides exist in mineral soils in large quantities. When soils become reducing, the metals bound to Fe and Mn oxides are transformed into readily available forms due to dissolution of Fe and Mn oxides. During flooding and drainage cycles of wetlands, the formation of iron oxyhydroxides is important in retaining metals in surface soils (Gambrell, 1994). 

The three examples of the effects of pedochemical weathering on the surface structures in soil clays just described illustrate the complexity of the reactive solid materials in natural soils. To these examples can be added many others, including the formation of iron oxyhydroxide or calcium carbonate coatings on the external surfaces (as opposed to interlayer surfaces) of phyllosilicates, the development of thick envelopes of colloidal organic matter on aggregates of metal oxides and aluminosilicates, and the... 

Membranes can act as both active and passive templates for the formation of well-defined nanostructures in a number of ways. In the biological realm, they have a limited role in the formation of nanowires, where virus capsids are much more effective, as described elsewhere in this volume (see Viruses as Self-Assembled Templates, Self-Processes). An interesting exception that takes place close to the membranes of living cells is the formation of iron oxyhydroxide (akaganeite, /1-FeOOH) in a natural ecosystem, in which polysaccharides are shown to be important as they are contained in the filaments of the inorganic material. It is believed that the sugar is extruded from the cell and then acts as a template to promote the formation of the mineral. On the other hand, entirely synthetic lipids can be used for the preparation of pipes of organically functionalized layered materials—clays —in... 

Misawa,T Hashimoto, K. Shimodaira, S. (1974) The mechanism of formation of iron oxide and oxyhydroxides in aqueous solutions at room temperature. Corrosion Sci. 14 131 — 149... 

The presence of iron oxyhydroxide coatings (i.e., Fe plaque, often dominated by ferrihydrite) on the surface of wetland plant roots is visual evidence that subsurface iron oxidation is occurring in otherwise anoxic wetland soils and sediments. Oxygen delivered via radial O2 loss may react with reduced iron in soil pore spaces to form oxidized iron that can be deposited on the plant roots as Fe plaque. Despite a long history of observing Fe plaque on wetland plant roots and understanding the basics of plaque formation [i.e., reaction of plant-transported O2 with Fe(II) in soils and sediments], it was largely assumed that plaque formation is predominately an abiotic (i.e., chemical) process because the kinetics of chemical oxidation can be extremely rapid (Mendelssohn et al., 1995). However, recent evidence has demonstrated that populations of lithotrophic FeOB are associated with Fe plaque and may play a role in plaque deposition. 

Combes J-M, Manceau A, Calas G (1986) Study of the local structure in poorly ordered precursors of iron oxyhydroxides. J de Physique (Colloque C8, Vol. 2) 697-C8/701 Combes J-M, Manceau A, Calas G (1989a) XAS study of the evolution of local order around iron(III) in the solution to gel to iron oxide (a-Fe203) transformation. PhysicaB (Amsterdam) 158 419-420 Combes J-M, Manceau A, Calas G (1990) Formation of ferric oxides from aqueous solutions A polyhedral approach by X-ray absorption spectroscopy II. Hematite formation from ferric gels. Geochim Cosmochim Acta 54 1083-1091... 

Bauminger and Harrison reviewed studies of the process of iron core formation in human and horse spleen ferritins using Mossbauer spectroscopy. It was demonstrated that iron deposition within ferrihydrite core in human and horse spleen ferritin started with Fe(ll) oxidation. This process was associated with ferroxidase center of H-chains. Further, an Fe(lll) compound and Fe(lll) jL-oxo-bridged dimers in ferroxidase centers of H-chains were found, which were intermediate compounds in the process of iron oxyhydroxide core formation in horse spleen ferritin. The steps leading to ferrihydrite core formation in human L- and H-ferritins were also identified and transfer between ferritin molecules was established [M2]. 

Hydrolysis reactions and the precipitation of iron oxyhydroxide phases also play a key role in the corrosion of metallic iron. Corrosion reactions can involve both ferrous and ferric iron hydrolysis species and the formation of surface coatings of either iron(ll) or iron(lll) (oxy)hydroxide phases. The understanding of corrosion and its effects has received a considerable amount of attention. 

The effect of metalloids on the corrosion resistance of alloys also varies with the stability of polyoxyanions contained in their films. Phosphorus and carbon contained in iron-chromium-melalloid alloys do not produce passive films of phosphate and carbonate in strong acids, and so do not interfere with the formation of the passive hydrated chromium oxyhydroxide... 

Fig. 15-5 Comparative adsorption of several metals onto amorphous iron oxyhydroxide systems containing 10 M Fej and 0.1 m NaNOs. (a) Effect of solution pH on sorption of uncomplexed metals, (b) Comparison of binding constants for formation of soluble Me-OH complexes and formation of surface Me-O-Si complexes i.e. sorption onto Si02 particles, (c) Effect of solution pH on sorption of oxyanionic metals. (Figures (a), (c) reprinted with permission from Manzione, M. A. and Merrill, D. T. (1989). "Trace Metal Removal by Iron Coprecipitation Field Evaluation," EPRI report GS-6438, Electric Power Research Institute, California. Figure (b) reprinted with permission from Balistrieri, L. et al. (1981). Scavenging residence times of trace metals and surface chemistry of sinking particles in the deep ocean, Deep-Sea Res. 28A 101-121, Pergamon Press.)...

Some metals are irreversibly adsorbed, probably via incorporation into the mineral phases, such as amorphous iron oxyhydroxides, as shown in Figure 11.6d. Some of these amorphous phases form by direct precipitation from seawater. As noted earlier, hydrothermal fluids are an important source of iron and manganese, both of which subsequently precipitate from seawater to form colloidal and particulate oxyhydroxides. Other metals tend to coprecipitate with the iron and manganese, creating a polymetallic oxyhydroxide. It is not clear the degree to which biological processes mediate the formation of such precipitates. Since the metals are incorporated into a mineral phase, this type of scavenging is better referred to as an absorption process. 

In very acidic solutions (pH < 2.4-3) with ionic strengths below 0.1 M and at 25 °C and 1 bar pressure, scorodite has a pK of about 25.83 0.07. The pK of amorphous Fe(III) arsenate is approximately 23.0 0.3 under the same conditions (Langmuir, Mahoney and Rowson, 2006). At higher pH values, scorodite dissolves incongruently, which means that at least one of its dissolution products precipitates as a solid. The incongruent dissolution of scorodite in water leads to the formation of Fe(III) (oxy)(hydr)oxide precipitates that is, Le(III) (hydrous) oxides, (hydrous) hydroxides and (hydrous) oxyhydroxides (Chapter 3). During the formation and precipitation of the iron(III) (oxy)(hydr)oxides, As(V) probably coprecipitates with them (Chapter 3 also see Section 2.7.6.3). The dissolution rate of scorodite at 22 °C in pH 2-6 water is slow, around 10—9 —10—10 mol m-2 s-1, which explains its presence in many mining wastes (Harvey et al., 2006). 

---