Al-hematite

The Bhf of the well crystalline Al-hematites produced by heating Fe-Al-oxinates at 700 °C (n = 8) showed a much higher correlation with Al-substitution (da Costa et al. 2001) ... 

TEM and differential X-ray line broadening (expressed by the ratio of the width at half height of the 104 relative to that of the 110 reflection) indicate that the thickness of the platy Al-hematite crystals decreases as Al/(Fe-t Al) increases (Schwertmann et al., 1977 Barron et al., 1984). It is this change in morphology, rather than the structural Al, which governs the IR spectra, in particular the shape factor and the absorp-... 

Al-hematites formed slowly from Al-ferrihydrite at 25 °C over 20 years, varied between rhombohedra at low substitution and multidomainic ellipsoids ca. 100 nm across with a grainy interior at higher substitution (Al/(Al-rFe) = 0.15) (Fig. 4.20e f) (Schwertmann et al. 2000). Allophane as a source of A1 had the same effect (Schwert-mann et al. 2000a). Mn substituted hematites grown from ferrihydrite were ellipsoidal in the presence of oxalate and platy in the presence of NaHCOa buffer (Cornell Gio-vanoli, 1987 Cornell et al., 1990). Cu substituted (0.09 mol mol" ) hematite grows as large (0.2 pm) rhombohedral crystals the crystal faces are most probably 102 or 104 (Fig. 4.20d) (Cornell Giovanoli, 1988). 

Schwertmann Pfab, 1994) (see Plate 6.II). Mn substituted hematites are blackish. In case of A1 substitution, the observed shift towards redder hues is due mainly to the associated decrease in particle size (Scheinost et al. 1999). Structural A1 does not significantly influence the hue and chroma of synthetic Al-hematite, although the crystals become lighter (Munsell value increases) (Barron Torrent, 1984 Kosmas et al, 1986). 

Fig. 8.4 Stability fields of Al-goethite and Al-hematite as a function of Al substitution.

Fig. 12.25 Di ssolution features of hematites Upper Undissolved (a) and partly dissolved (b c) synthetic Al-hematite (AI/(Fe+AI) = 0.094 mol moT j in dithionite/citrate/bicarbonate at25 (Araki Sch A/ertmann unpubl.), Lo A/er Undissolved and partly dissolved hematite from a redoxomorphic subsoil of a typical Hapludalf on Permian mudstone, Ohio (Bigham et al., 1991, A/ith permission).

Morris et al. (1991) obtained hematite of very small particle size ( 10 nm), termed nanophase by slow thermal decomposition in air of tri-Ee -acetato-hy-droxy-nitrate. XRD shows only two broad lines as in a 2-line ferrihydrite, but the magnetic hyperfine field at 4.2 K of 50.4 T appears to be more in agreement with poorly crystalline hematite. Well-crystalline hematite and Al-hematite were produced by decomposing Ee-Al-oxinates at 700 °C (da Costa et al. 2001). 

Y. Tardy and D. Nahon, Geochemistry of laterites, stability of Al-goethite, Al-hematite, and Fe3+-kaoIinite in bauxites and ferricretes An approach to the mechanism of concretion formation, Am. J. Sci. 285 865 (1985). 

The crystallinity of the Al hematite changes with the level of Al in the structure a maximum is often obtained at low to medium substitution (5-10 mol%). This corresponds to a minimum in XRD peak broadening and a maximum in y-ray absorption (Schwertmann et al., 1979 DeGrave et al., 1982 Murad and Schwertmann, 1986). Both X-ray diffraction peaks (Fig. 10-2) and IR absorption bands (Fig. 10-3) show a shift due to Al-for-Fe substitution. The surface area of the hematites is around 40 to 50 m /g. 

Table 7.3. Shock-modified powders Crystallite size, strain, and static magnetization data on hematite (after Williamson et al. [86W03]).

Fig. 7.6. The weak ferromagnetic (WF) fraction (high temperature form) of hematite provides a sensitive measure of shock modification. Sample 31G836 is an 8 GPa experiment. Sample 29G836 is a 17 GPa experiment, while 17G846 is a 27 GPa sample (after Williamson et al. [86W03]).

From Fig.2 (a), A solid phase transformation fiom hematite, Fc203 to magnetite, Fe304, is observed, indicating that the active sites of the catalj are related to Fc304. Suzuki et. al also found that Fe304 plays an important role in the formation of active centers by a redox mechanism [6]. It is also observed that the hematite itself relates to the formation of benzene at the initial periods, but no obvious iron carbide peaks are found on the tested Li-Fe/CNF, formation of which is considered as one of the itsisons for catalyst deactivation [3,6]. 

The liquid-phase reduction method was applied to the preparation of the supported catalyst [27]. Virtually, Muramatsu et al. reported the controlled formation of ultrafine Ni particles on hematite particles with different shapes. The Ni particles were selectively deposited on these hematite particles by the liquid-phase reduction with NaBFl4. For the concrete manner, see the following process. Nickel acetylacetonate (Ni(AA)2) and zinc acetylacetonate (Zn(AA)2) were codissolved in 40 ml of 2-propanol with a Zn/Ni ratio of 0-1.0, where the concentration of Ni was 5.0 X lO mol/dm. 0.125 g of Ti02... 

Fig. 1.15. Diagram showing the homogenization temperature of fluid inclusions vs. the iron content of the host sphalerite growth zone for sample locality NJP-X on the OH vein. The line shows the predicted iron content of the sphalerite if the sulfur fugacity of the system had been buffered by the triple point — Fe-chlorite (daphnite), pyrite, hematite (Hayba et al., 1985).

Figure 1.33. Frequency (number of analyses) histogram for Fc203 (wt%) of epidote from the Kuroko basalt. A epidote coexisting with albite, B epidote coexisting with chlorite, C epidote coexisting with pyrite, D epidote coexisting with hematite and calcite (Shikazono et al., 1995).

The predominant gangue minerals vary with different types of ore deposits quartz, chalcedonic quartz, adularia, calcite, smectite, interstratified mica/smectite, interstratified chlorite/smectite, sericite, zeolites and kaolinite in Au-Ag rich deposits chlorite, quartz, sericite, carbonates (calcite, rhodoehrosite, siderite), and rare magnetite in Pb-Zn rich deposits chlorite, serieite, siderite, hematite, magnetite and rare epidote in Cu-rich deposits (Sudo, 1954 Nagasawa et al., 1976 Shikazono, 1985b). 

Figure 1.196. /oj-pH ranges for hot-spring-type deposits and low sulfidation-type deposits. Temperature = 250°C, ES = 0.01 mol/kg H2O, ionic strength = 1. Ka kaolinite, Al alunite, SI liquid sulfur, Kf K-feldspar, Hm hematite, Mt magnetite, Py pyrite, Po pyrrhotite. Bn bomite, Cp chalcopyrite. 

Main opaque minerals are chalcopyrite, pyrite, pyrrhotite, sphalerite and bornite (Table 2.22). These minerals commonly occur in massive, banded and disseminated ores and are usually metamorphosed. Hematite occurs in red chert which is composed of fine grained hematite and aluminosilicates (chlorite, stilpnomelane, amphibole, quartz) and carbonates. The massive sulfide ore bodies are overlain by a thin layer of red ferruginous rock in the Okuki (Watanabe et al., 1970). Minor opaque minerals are cobalt minerals (cobaltite, cobalt pentlandite, cobalt mackinawite, carrollite), tetrahedrite-tennantite, native gold, native silver, chalcocite, acanthite, hessite, silver-rich electrum, cubanite, valleriite , and mawsonite or stannoidite (Table 2.22). 

The main alteration minerals surrounding Kuroko ore body are K-mica, K-feldspar, kaolinite, albite, chlorite, quartz, gypsum, anhydrite, and carbonates (dolomite, calcite, magnesite-siderite solid solution), hematite, pyrite and magnetite. Epidote is rarely found in the altered basalt (Shikazono et al., 1995). It contains higher amounts of ferrous iron (Fe203 content) than that from midoceanic ridges (Shikazono, 1984). 

Figure 7. U(VI) sorption onto muscovite (7a, Schmeide et al. 2000) and hematite (7b, Lenhart and Honeyman 1999) in the absence (U) and in the presence of humic acid (U+HA). 7a [U02 ] = 1 pmol/L, [HA] = 5 mg/L, muscovite content of about 1.2g/L. Complexation of U with HA in solution and onto mineral surface may influence U sorption. For instance, U sorption onto muscovite is enhanced in presence of HA at low pH. 7b [U] = 1 jamol/L, [HA] = 10 mg/L. Hematite content in solution = 0.9 and 9g/L. Uptake of U increases with increasing hematite content. In presence of hematite, an increase of U sorption onto hematite is observed at low pH, especially at low hematite content.

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