Goethite iron oxides

Plate 5.2 Crusts of iron oxide (goethite) coating stream bed. Drainage from Parys Mountain, copper mine Anglesey, UK. Photograph courtesy of J. Andrews. 

The major constituents of soils are sesquioxides and clay minerals. Iron oxide (goethite) was synthesized by a method described by Gerth [4] and manganese oxide (manganite) was prepared by a method described by McKenzie [5]. The clay mineral montmorillonite was obtained from Wyoming, USA, while kaolinite was obtained from Ward Corp., USA. Organic substances were destroyed by a pretreatment of the clay minerals with HjOj. The surfaces were loaded with calcium chloride and adjusted to pH 7. 

Minerals. Iron-bearing minerals are numerous and are present in most soils and rocks. However only a few minerals are important sources of iron and thus called ores. Table 2 shows the principle iron-bearing minerals. Hematite is the most plentiful iron mineral mined, followed by magnetite, goethite, siderite, ilmenite, and pyrite. Siderite is unimportant in the United States, but is an important source of iron in Europe. Tlmenite is normally mined for titania with iron as a by-product. Pyrite is roasted to recover sulfur in the form of sulfur dioxide, leaving iron oxide as a by-product. 

Iron Oxide Reds. From a chemical point of view, red iron oxides are based on the stmcture of hematite, a-Fe202, and can be prepared in various shades, from orange through pure red to violet. Different shades are controlled primarily by the oxide s particle si2e, shape, and surface properties. Production. Four methods are commercially used in the preparation of iron oxide reds two-stage calcination of FeS047H2 O precipitation from an aqueous solution thermal dehydration of yellow goethite, a-FeO(OH) and oxidation of synthetic black oxide, Fe O. ... 

Iron Oxide Yellows. From a chemical point of view, synthetic iron oxide yellows, also known as iron gelbs, are based on the iron(III) oxide—hydroxide, a-FeO(OH), known as goethite. Color varies from light yellows to dark buffs and is primarily determined by particle size, which is usually between 0.1 and 0.8 p.m. Because of their resistance to alkahes, these are used by the building industry to color cement. Thermally, iron oxide yellows are stable up to 177°C above this temperature they dehydrate to iron(III) oxide ... 

In the wetlands of Idaho, the formation of an Fe(III) precipitate (plaque) on the surface of aquatic plant roots (Typha latifolia, cat tail and Phalaris arundinacea, reed canary grass) may provide a means of attenuation and external exclusion of metals and trace elements (Hansel et al, 2002). Iron oxides were predominantly ferrihydrite with lesser amounts of goethite and minor levels of siderite and lepidocrocite. Both spatial and temporal correlations between As and Fe on the root surfaces were observed and arsenic existed as arsenate-iron hydroxide complexes (82%). 

Liu F, De Cristofaro A, Violante A (2001) Effect of pH phosphate and oxalate on the adsorption/desorption of arsenate on/from goethite. Soil Sci 166 197-208 Livesey NT, Huang PM (1981) Adsorption of arsenate by soils and its relation to selected properties and anions. Soil Sci 131 88-94 Manceau A (1995) The mechanism of anion adsorption on iron oxides Evidence for the bonding of arsenate tetrahedra on free Fe(0, OH)6 edges. Geochim Cosmochim Acta 59 3647-3653. 

The primary anion studied in both the titration calorimetry7 and CIR-FTIR experiments reported here was the salicylate (2-hydroxybenzoate) ion (SAL). Acidity constants for salicylic acid are pK = 3.0 and pK = 13 (12), and the aqueous solubility of salicylic acid is 2.4 g/L, while that of NaSAL is 975 g/L. SAL has been shown to adsorb on both iron oxides (13) and aluminum oxides (14). Several other anions were also studied, and results for these anions are given as needed to illuminate certain features of the salicylate-goethite adsorption process. 

Klupinski et al. (2004) report a laboratory experiment on the degradation of a fungicide, pentachloronitrobenzene (C Cl NO ), in the presence of goethite and iron oxide nanoparticles this study was intended to illustrate the fate of organic agrochemical contaminants in an iron-rich subsurface. To compare the effects of iron with and without a mineral presence, experiments were performed using... 

Fig. 16.9 Change in first-order rate constant k for the reduction of CgCl NO as a result of varying goethite content in media with 473 iM Fe(II) and 200mM NaCl (pH 6.96). Error bars to indicate 95% confidence intervals would be smaller than symbols. Reprinted with permission from Klupinski TP, Chin YP, Traina S J (2004) Abiotic degradation of pentachloronitrobenzene by Fe(II) Reactions on goethite and iron oxide nanoparticles. Environ Sci Technol 38 4353-4360. Copyright 2004 American Chemical Society...

Table 16.3 Names, abbreviations, pseudo-first-order rate constants, and half-lives of polyhalo-genated alkanes in Fe(II)/goethite suspension. Experimental conditions 25 m L" goethite, pH 7.2, tgq>24 h. Fe(II) = 1 mM. b Standard deviation, c number of replicates, d t =5 h. Reprinted with permission from Pecher K, Haderline SB, Schwarzenbach RP (2002) Reduction of polyhalo-genated methanes by surface-bound Fe(II) in aqueous suspensions of iron oxides. Environ Sci Technol 36 1734-1741. Copyright 2002 American Chemical Society...

Hydrohetaerolite Zn2Mn ""408 HjO PBF 1 717 Limonite = hydrous iron oxides, mostly goethite PBF 1 685 Manganite MnO(OH) MW 95... 

During conversion of goethite to hematite only small fractionation effects seem to occur, because most of the oxygen remains in the solid (Yapp 1987). Thus, in principle it should be possible to reconstruct the sedimentary environment of iron oxides from Precambrian banded iron formations (BIF). By analyzing the least metamorphosed BlFs, Hoefs (1992) concluded, however, that the situation is not so simple. Infiltration of external fluids during diagenesis and/or low temperature metamor-... 

Yapp Cl (1983) Stable hydrogen isotopes in iron oxides - isotope effects associated with the dehydration of a natural goethite. Geochim Cosmochim Acta 47 1277-1287... 

Certain iron oxides are isostructural with other metal oxides. Goethite, for example, is isostructural with diaspore (a-AlOOH) and hence, is sometimes referred to as having the diaspore structure. Iron oxides and their isostructural metal oxides are listed in Table 2.1. 

Structural relationships exist between certain planes in the hematite structure and those in other iron oxides, namely magnetite and goethite (Tab. 2.6). There is, for example, a relationship between the (111) plane of magnetite and (001) plane of hema-... 

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