The Major Iron Oxides

The basic structural unit of all Fe oxides is an octahedron, in which each Fe atom is surrounded either by six O or by both O and OH ions. The O and OH ions form layers which are either approximately hexagon-ally close-packed (hep), as in goethite and hematite, or approximately cubic close-packed (cep), as in lepidocrocite and maghemite. In both hep and cep stuctures, tetrahedral interstices also exist between three O or OH in one plane and the anion in the plane above. The two hep forms, goethite and hematite, are termed a-phases, whereas the corresponding cep forms, lepidocrocite and maghemite, are termed y-phases. 

The Fe in the octahedral position may be partly replaced by other triva-lent metal cations of similar size, for example, Mn , Cr and without modifying the structure isomorphous substitution). In this way solid solutions between pure end members (such as FeOOH and 

Ionic radius depends on whether the ion is in the high spin or low spin state. In the Fe oxide structure (and where a choice exists), the ions listed adopt a high spin state. 

These ions display the Jahn-Teller effect which leads to distortion of the coordination sphere of the ion. 

The various Fe oxides differ mainly in the arrangement of the Fe(0,0H)6 oetahedra. 

---

Other Minerals. In this work only the minerals mentioned above were detected using Mossbauer spectroscopy. However, in heavily weathered coals and coal refuse the presence of iron oxides (hematite and, to a lesser extent, magnetite) was observed. The Mossbauer parameters for the major iron oxides are given in Table IV. 

For all these purposes reliable methods of producing pure iron oxides are required. This book aims at fulfilling this need. It sets out reliable, convenient preparative methods for s3mthesizing the major iron oxides. The emphasis is on techniques and equipment that are readily accessible to... 

Table 1-1. The Major Iron Oxides and Oxide Hydroxides...

Physical and chemical properties of the major iron oxides are summarized in Table 1-3. 

Reforming is completed in a secondary reformer, where air is added both to elevate the temperature by partial combustion of the gas stream and to produce the 3 1 H2 N2 ratio downstream of the shift converter as is required for ammonia synthesis. The water gas shift converter then produces more H2 from carbon monoxide and water. A low temperature shift process using a zinc—chromium—copper oxide catalyst has replaced the earlier iron oxide-catalyzed high temperature system. The majority of the CO2 is then removed. 

Iron Blocks. Chemically, iron blacks are based on the binary iron oxide, FeOFe2 O3. Although the majority is produced in the cubical form, these can also be produced in acicular form. Most of the black iron oxide pigments contain iron(III) oxide impurities, giving a higher ratio of iron(III) than would be expected from the theoretical formula. 

C03-0030. One of the major iron ores is an oxide with the following percentage composition Fe, 72.36% and O, 27.64%. What is the chemical formula of this ore ... 

LDL becomes oxidized in vivo. There is evidence that LDL is protected against oxidation in plasma by water-soluble antioxidative substances, such as ascorbic acid, uric acid, or bilirubin. Thus, it is likely that the majority of oxidative modification of LDL occurs in the artery wall, where LDL is largely isolated from the plasmatic antioxidants. Recent evidence suggests that metal ions (copper or iron) and the enzymes myeloperoxidase and lipoxygenase play major parts in the modification of LDL [161]. 

Iron occurs abundantly in several materials, mainly in the form of oxides, carbonate, silicates, and sulfides, These are shown in Table 2, Most of the ores shown In the table are described under separate alphabetical listings in this volume. Briefly, the major iron-hearing materials are ... 

In natural anoxic environments, the major alternative oxidants are iron(III) and manga-nese(IV) oxides and hydroxides. Both are common in natural systems, as crystalline or amorphous particles or coatings on other particles. In the absence of photocatalysis, however, iron and manganese oxides are weak oxidants. As a result, they appear to react at significant rates only with phenols and anilines (45, 59-64). 

Selective extractions, chemical equilibria calculations, and crystallization measurements presented here imply that the hydrous iron oxides, even in the carbonate dominated Genesee River, play a major part in inorganic phosphorus transport by sediments in the fluvial system. Saturation levels of inorganic phosphate and calcium carbonate minerals in the Genesee River... 

Table 6 shows the major metal oxides and the iron oxide impurity levels of typical borosilicate Type I glass. Up to 0.05% by weight (500 ppm) iron oxide as Fe O may exist in the borosilicate Type I glass. Thus, the increase in iron levels with time likely reflects a slow leaching of iron from the glass vial. Consistent with this explanation is that similar increases in silicon, aluminum, calcium, and barium levels are also observed in older product lots as shown in Table 6. Note that these nontransition metal ions are not known to participate in the type of reactions depicted in Figure 6. Furthermore, it is not clear if the expected increase in iron leaching from amber vials (Table 6) will be readily compensated for by the reduced light transmission at the causative wavelengths offered by utilizing the amber vial as the primary package.

Figure 7 Two-liquid field in the Fe-S-P system as determined by Raghavan (1988) (hatched line) and Chabot and Drake (2000) (white area). Chabot and Drake performed their experiment at more oxidizing condition—assumed relevant for group IIIAB iron meteorites. Also shown are the trends followed by the major iron meteorite groups. Note that all groups eventually enter the two-liquid field (reproduced by permission of the Meteoritical Society from...

Water samples from the Main Stem and the South Fork of the Coeur d Alene River, Idaho, USA, which were contaminated with Sb and As, and the other heavy metals from the local mining operation, showed high levels of Sb (0.23-8.25 ppb) and As (0.11 -1.64 ppb). The major inorganic Sb species was Sb(V) in all three branches of the river. Leaching of Sb and As species from the contaminated Main Stem sediments depended on the pH values of the water as well as on the free iron oxides and manganese oxides present in the sediments ... 

The major iron storage protein, ferritin, has been extensively studied (48) and shown to consist of a hollow, spherical proteinaceous shell surrounding an iron(III) oxide core. The other iron storage protein, hemosiderin, has received rather less attention, but, for normal hemosiderin, techniques such as Fe Mossbauer spectroscopy and electron diffraction (49) indicate the presence of a smaller ferritin-like core. 

The major elements (Chapter 3) are the elements which predominate in any rock analysis. They are Si, Ti, Al, Fe, Mn, Mg, Ca, Na, K and P, and their concentrations are expressed as a weight per cent (wt%) of the oxide (Table 1.1). Major element determinations are usually made only for cations and it is assumed that they are accompanied by an appropriate amount of oxygen. Thus the sum of the major element oxides will total to about 100 % and the analysis total may be used as a rough guide to its reliability. Iron may be determined as FeO and Fe203, but is sometimes expressed as total Fe and given as either FeO( t) or Fe2 3(t ) ... 

---