Ferric iron oxides

The tubes in the EDC pyrolosis furnace are packed with charcoal pellets impregnated with ferric (iron) oxide. The EDC is pumped through at about 900—950°F and 50 psi. The conversion of EDC, i.e, how much of.it disappears, is about 50%, and the yield of VC, how much of the disappearing EDC gets converted to VC, is about 95—96%. (See the Appendix if you haven t yet read about the difference between yield and. conversion.)... 

Ferric (iron) oxide This is plain old rust. Take a trip to the dump or junkyard with a file and paper cup. Scrape the rust off of any old iron or steel object. 

As Berner (36) pointed out in his classic work, the formation of pyrite is coupled to a process in which free sulfide is oxidized to form polysulfides, which again react with FeS to form pyrite. In this study elemental sulfur was the oxidant. However, elemental sulfur was always less than 1% of the total sulfur content in the study of White et al. (35). The findings of the experimental studies discussed on the interaction between H2S and ferric oxides (20-23), in combination with the field observations, suggest a mechanism in which ferric iron oxides are the oxidants to form polysulfides and subsequently pyrite. 

In general, the minerals now identified as chamosite are found in iron ore bodies of sedimentary origin (e.g., Maynard, 1986 Fernandez and Moro, 1998 Wiewora et al, 1998 Kim and Lee, 2000). Chamosite associated with iron oxides appears to follow a compositional trend from iron oxides plus kaolinite to chlorite, as indicated in Figure 8, using the data of Velde (1989). The recombination of iron oxide in the presence of kaolinite gives an aluminous, ferrous mineral, chamosite. This mineral is formed under burial conditions where ferric iron oxide is reduced to feiTous iron which is rapidly incorporated into a 7 A chlorite mineral. Both chamosite and berthierine result from the reduction of ferric iron to ferrous iron. 

Dzombak, D.A. Morel, F.M.M. (1990) Surface Complexation Modelling Hydrous Ferric iron Oxide. New York John Wiley Sons. 

Figure 28. Hypothetical anaerobic nitrogen cycle based on the following thermodynamically permissible reactions (1) ammonium oxidation to dinitrogen by carbon dioxide,. sulfate or ferric iron (no evidence at present, possibly kinetically limited) (2) dinitrogen fixation by various organic and inorganic reductants (known) (3) ammonium oxidation by nitrite or nitrate producing dinitrogen (known) (4) denitrification (known) (5) nitrite or nitrate respiration (known) (6) ferric iron oxidation of ammonium to nitrite or nitrate (no evidence at present) (7) nitrate assimilation (known) (8) ammonium assimilation and di.s,similation (known) (Fenchel etai, 1998).

Ferric iron oxidation of ammonium to nitrite or nitrate ... 

Table 7.7. Surface properties of hydrous ferric iron oxides. Data from Dzombak and Morel (1990).

Table 7.10. Results of minteqa2 calculations of adsorption onto hydrous ferric iron oxide (HFO).

Nickel laterite is nickel mineral changed by weathering, etching, enrichment, and then it turns loose clay-like, composed of iron, aluminum, silicon, and some hydrous oxides. The element and moisture content are rich in this kind of ore. The elemental composition and content (Table 1) can be obtained by XRF elemental analysis and chemical analysis.XRD demonstrated that host minerals of the iron-enriched and magnesium-depleted version of laterites are mainly ferric iron oxides, typically goethite, FeO(OH), and nickel embedded in the mineral is mainly as the pattern of NiO (Figure 1). All of the samples came from Baosteel. 

FIGURE 2 A scanning electron micrograph of the metal-reducing bacterium, Shewanella oneidensis strain MR-1, attached to a steel surface. As steel corrodes, ferric iron oxides are produced. MR-1 can reduce these minerals during respiration. 

Hydrogenis prevented from forming a passivating layer on the surface by an oxidant additive which also oxidizes ferrous iron to ferric iron. Ferric phosphate then precipitates as sludge away from the metal surface. Depending on bath parameters, tertiary iron phosphate may also deposit and ferrous iron can be incorporated into the crystal lattice. When other metals are included in the bath, these are also incorporated at distinct levels to generate species that can be written as Zn2Me(P0 2> where Me can represent Ni, Mn, Ca, Mg, or Fe. 

Iron oxide yellows can also be produced by the direct hydrolysis of various ferric solutions with alkahes such as NaOH, Ca(OH)2, and NH. To make this process economical, ferric solutions are prepared by the oxidation of ferrous salts, eg, ferrous chloride and sulfate, that are available as waste from metallurgical operations. The produced precipitate is washed, separated by sedimentation, and dried at about 120°C. Pigments prepared by this method have lower coverage, and because of their high surface area have a high oil absorption. 

Iron Browns. Iron browns are often prepared by blending red, yellow, and black synthetic iron oxides to the desired shade. The most effective mixing can be achieved by blending iron oxide pastes, rather than dry powders. After mixing, the paste has to be dried at temperatures around 100°C, as higher temperatures might result in the decomposition of the temperature-sensitive iron yellows and blacks. Iron browns can also be prepared directiy by heating hydrated ferric oxides in the presence of phosphoric acid, or alkaU phosphates, under atmospheric or increased pressure. The products of precipitation processes, ie, the yellows, blacks, and browns, can also be calcined to reds and browns. 

Water. Based on the overall balanced equation for this reaction, a minimum of one mole of water per mole of nitro compound is required for the reduction to take place. In practice, however, 4 to 5 moles of water per mole of nitro compound are used to ensure that enough water is present to convert all of the iron to the intermediate ferrous and ferric hydroxides. In some cases, much larger amounts of water are used to dissolve the amino compound and help separate it from the iron oxide sludge after the reaction is complete. 

Thiocyanates are rather stable to air, oxidation, and dilute nitric acid. Of considerable practical importance are the reactions of thiocyanate with metal cations. Silver, mercury, lead, and cuprous thiocyanates precipitate. Many metals form complexes. The deep red complex of ferric iron with thiocyanate, [Fe(SCN)g] , is an effective iadicator for either ion. Various metal thiocyanate complexes with transition metals can be extracted iato organic solvents. 

With aluminum sulfate, optimum coagulation efficiency and minimum floe solubiUty normally occur at pH 6.0—7.0. Iron coagulants can be used successfully over the much broader pH range of 5.0—11.0. If ferrous compounds are used, oxidation to ferric iron is needed for complete precipitation. This may require either chlorine addition or pH adjustment. 

Foulants enter a cooling system with makeup water, airborne contamination, process leaks, and corrosion. Most potential foulants enter with makeup water as particulate matter, such as clay, sdt, and iron oxides. Insoluble aluminum and iron hydroxides enter a system from makeup water pretreatment operations. Some well waters contain high levels of soluble ferrous iron that is later oxidized to ferric iron by dissolved oxygen in the recirculating cooling water. Because it is insoluble, the ferric iron precipitates. The steel corrosion process is also a source of ferrous iron and, consequendy, contributes to fouling. 

Reagents similai to those used in the analysis of chloiine are commonly employed in the quantitation of gaseous and aqueous chloiine dioxide as well as its reaction coproducts chlorine, chlorite, and chlorate. The volatihty of the gas from aqueous solutions as well as its reactivity to light must be considered for accurate analysis. Other interferences that must be taken into account include other oxidizers such as chloramine, hydrogen peroxide, permanganate, and metal impurities such as ferrous and ferric iron. 

Brown combinations usually contain iron with chromium, zinc, titanium, or aluminum. There are a few without iron that contain chromium, antimony, tin, zinc, manganese, or aluminum. They range from tight tans to dark chocolate. The shades ate not as red as ferric oxide, but the browns are far superior to hydrated iron oxide in brightness and thermal stability. 

Metal depositors. Metal-depositing bacteria oxidize ferrous iron (Fe ) to ferric iron (Fe ). Ferric hydroxide is the result. Some bacteria oxidize manganese and other metals. Gallionella bacteria, in particular, have been associated with the accumulation of iron oxides in tubercles. In fact, up to 90% of the dry weight of the cell mass can be iron hydroxide. These bacteria appear filamentous. The oxide accumulates along very fine tails or excretion stalks generated by these organisms. 

The ferric oxide is impregnated on wood chips, which produces a solid bed with a large ferric oxide surface area. Several grades of treated wood chips are available, based on iron oxide content. The most common grades are 6.5-, 9.0-, 15.0-, and 20-lb iron oxide/bushel. The chips are contained in a vessel, and sour gas flows through the bed and reacts with the ferric oxide. Figure 7-3 shows a typical vessel for the iron sponge process. 

Eisenozyd, n. iron oxide, specif, ferric oxide, iron(Ul) oxide. — salpetersaures —, ferric nitrate, iron(III) nitrate (and so for other salts). 

Iron-Oxidizing Bacteria. These are aerobic organisms capable of growing in systems with less than 0.5 ppm oxygen. They oxidize iron from ferrous to the ferric state by the following mechanism ... 

The carbon dioxide produced can contribute to the corrosion of metal. The deposits of ferric hydroxide that precipitate on the metal surface may produce oxygen concentration cells, causing corrosion under the deposits. Gallionalla and Crenothrix are two examples of iron-oxidizing bacteria. 

The structure of millscale consists of three superimposed layers of iron oxides in progressively higher states of oxidation from the metal side outwards, viz. ferrous oxide (FeO) on the inside, magnetite (Fe304) in the middle and ferric oxide (Fe203) on the outside. The relative portions of the three oxides vary with the rolling temperatures. A typical millscale on 9.5 mm mild steel plate would be about 50/tm thick, and contain approximately 70% FeO, 20% Fej04 and 10% FejOj. 

---