Magnetite chemical analysis

To model the brine s chemistry, we need to estimate its oxidation state. We could use the ratio of sulfate to sulfide species to fix ao2 > but chemical analysis has not detected reduced sulfur in the brine, which is dominated by sulfate species. A less direct approach is to assume equilibrium with a mineral containing reduced iron or sulfur, or with a pair of minerals that form a redox couple. Equilibrium with hematite and magnetite, for example,... 

Malucelli, F. Terribile, F. Colombo, C. (1999) Mineralogy, micromorphology and chemical analysis of andosols on the Island of Sao Miguel (Azores). Geoderma88 73-98 Mamedov, A. Ostrander, J. Aliev, F. Kotov, N.A. (2000) Stratified assemblies of magnetite nanoparticles and montmorillonite prepared by layer-by-layer assembly. Langmuir 16 3941-3949... 

The composition of the resulting magnetite is close to stoichiometric as indicated by chemical analysis (Fe2,o8Feo.9204), Mossbauer spectroscopy (Fe2,o3Feo.9704), and unit cell edge length (0.83997(3) nm). The crystals form cubes, bounded by 111 faces and vary in size between 0.05-0.2 p.m (Fig. 11-2) the surface area is 4 m /g. The XRD lines are sharp... 

FeCb (instead of FeS04) also yields magnetite. Oxidation at RT instead of at 90 C gave smaller crystals (ca. 50 nm) which chemical analysis, unit cell size and magnetic hyperfine properties showed to be partially... 

X-ray diffraction analysis of the Fei xO catalyst before reduction shows that only wiistite is present in the XRD spectrum which shows only three Fei xO peaks (I/Ig = 36, 100 and 38, 29 = 42.18°, 49.10°, and 71.90°, respectively) as illustrated in Fig. 1.10(a), while the Fe304 phase disappears completely, though it is expected to exists according to chemistry when Fe +/Fe < oo. It is due to the fact that Fe + in the samples does not compose an independent magnetite phase, but dissolves into the wiistite phase non-stoichiometrically. This indicates that, when Fe +/Fe is higher than about 3.5, iron oxides transfer to the non-stoichiometric ones with iron cation defects, namely wiistite phase expressed as Fei xO, where x is the defect concentrations of the Fe + iron cations. From a solid-chemistry viewpoint, Fei xO is a solid solution of Fe2 03 and FeO, therefore x value may be calculated by chemical analysis. 

Evidence for the presence of A1 dissolved in the magnetite phase has been found by X-ray powder diffraction [27,28, 38-42, 53] and by chemical analysis of powders of varying particle size [54]. The solubility of A1 in the (Fe,Al)3 04-phase has been determined to be 30 atom% A1 [55] from measurement of the Curie temperature and 50 atom % Al[55], or 67 atom % Al[39] from measurement of the X-ray powder diffraction lattice constant. Other studies have indicated homogeneous solution of A1 in magnetite, at least for small amounts of A1 [56] and not too high temperatures [57]. 

The influence of the Fe2+/Fe3+ molar ratio on the characteristics of magnetite particles obtained by co-precipitation of Fe2+ and Fe3+ (composition, size, morphology and magnetic properties) was studied by Jolivet (Jolivet et al., 1992). Chemical sp>ecies in different proportions were precipitated with ammonia solution to pH ll. The analysis of the products obtained with different Fe2+/Fe3+ molar ratios, in the range 0.10-0.50, concluded that for values lower than 0.30 two different phases coexist ... 

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