Iron oxides in tropical soils on various parent materials

Clay Minerals ◽  
2007 ◽  
Vol 42 (4) ◽  
pp. 437-451 ◽  
Author(s):  
W. Wiriyakitnateekul ◽  
A. Suddhiprakarn ◽  
I. Kheoruenromne ◽  
M. N. Smirk ◽  
R. J. Gilkes
Keyword(s):  
Iron Oxides ◽  
Crystal Size ◽  
Tropical Soils ◽  
Parent Materials ◽  
Fe Oxides ◽  
Al Substitution ◽  
Cell Dimensions ◽  
Basaltic Soils ◽  
Aluminium Substitution ◽  
Unit Cell Dimensions

AbstractTwenty nine Fe oxide concentrates of Thai soils formed on basalt, sandstone, shale/limestone and granite were investigated. Goethite and hematite are relatively more abundant in granitic and basaltic soils, respectively. Values of Feo/Fed range from 0.01 to 0.28 indicating that free Fe oxides are mostly crystalline.There are no systematic differences in unit-cell dimensions for goethite and hematite in soils on different parent materials. Mean crystallite dimensions calculated from the 110 reflections are greater for hematite than for goethite. Aluminium substitution varies from 8 to 24 mole% for goethite and from 4 to 17 mole% for hematite. The dehydroxylation temperature for goethite ranges from 285ºC to 320ºC. The goethite in basaltic soils has a smaller crystal size and Al substitution, as well as a lower dehydroxylation temperature, compared to soils on other parent materials. The dehydroxylation temperature of goethite is positively related to Al substitution (R = +0.58), MCD110 (R = +0.49) and Ald (R = +0.53). The Mn, Ni, Cr, V and P in these soils occur in Fe oxides rather than as discrete minerals.

Properties of iron oxides in red Oxisols and red Ultisols as affected by rainfall and soil parent material

Soil Research ◽  
2006 ◽  
Vol 44 (1) ◽  
pp. 63 ◽  
Author(s):  
P. Trakoonyingcharoen ◽  
I. Kheoruenromne ◽  
A. Suddhiprakarn ◽  
R.J. Gilkes
Keyword(s):  
Iron Oxides ◽  
Crystal Size ◽  
Tropical Soils ◽  
Parent Material ◽  
Line Broadening ◽  
X Ray Diffraction ◽  
Parent Materials ◽  
Soil Parent Material ◽  
Al Substitution ◽  
Aluminum Substitution

Tropical soils developed from various parent materials and under various rainfalls were analysed to identify whether these environmental factors influence the properties of the iron oxides. Iron contents of the soils range from 5 to 134 g/kg, with hematite and goethite being the major secondary iron minerals. Hematite is the dominant iron oxide in all soils developed on limestone irrespective of rainfall, whereas for other parent materials the relative abundance of goethite tends to increase with rainfall. Aluminum substitution in goethite and hematite ranges from 13 to 21 mol% and 7 to 15 mol%, respectively. The mole% Al substitution in hematite is about half the level for goethite in the same soil. Crystal size estimated from X-ray diffraction line broadening ranges from 12 to 47 nm for goethite and from 15 to 44 nm for hematite. Similar sizes were obtained by electron microscopy. The properties of the iron oxides did not vary systematically with parent material or rainfall and are similar to those described by other workers for red tropical soils on diverse parent materials.

The influence of aluminium on iron oxides: X. properties of Al-substituted goethites

Clay Minerals ◽  
1984 ◽  
Vol 19 (4) ◽  
pp. 521-539 ◽  
Author(s):  
D. G. Schulze ◽  
U. Schwertmann
Keyword(s):  
Crystal Size ◽  
Structural Defects ◽  
Crystal Thickness ◽  
Bending Vibrations ◽  
Average Temperature ◽  
Al Substitution ◽  
Cell Dimensions ◽  
The Mean ◽  
Unit Cell Dimensions ◽  
Xrd And Tem

AbstractFifty-seven goethites, synthesized by a variety of procedures and with Al substitutions of 0–33 mole%, were characterized by XRD, IR, DTA, TEM and chemical techniques. Most of the properties measured showed significant intercorrelations. Mole% Al substitution (measured chemically) did not explain all the relationships among variables, but the inclusion of Δa, defined as the observed a dimension minus the a dimension predicted by the Vegard rule, explained much of the variation not explained by Al substitution. OH stretching frequency, in particular, was better correlated with Δa than the Al substitution or other properties. The properties of the goethites could best be explained by a combination of Al substitution and structural defects, with Δa being a measure of the defects. In general, the effect of structural defects was opposite to that of Al substitution. Increase in Al substitution led to a decrease in all three unit-cell dimensions and OH stretching frequency and to an increase in the distance between the two OH bending vibrations (δOH-γOH) and the temperature of dehydroxylation. Increase in structural defects, on the other hand, caused the a dimension, Δa, and OH stretching frequency to increase and δOH-γOH and the average temperature of dehydroxylation to decrease. Crystal size tended to decrease with increases in both Al substitution and structural defects. Surface area was significantly correlated with the reciprocal of the mean crystal thickness in the a direction. Comparison of XRD and TEM data showed that many samples consisted of crystals with several coherently scattering domains. The nature of the defects, i.e. whether they occur primarily in the interdomain areas or whether they are also distributed throughout the coherently diffracting domains, could not be determined.

Properties of iron-oxides from red soils derived from volcanic tuff in West Java

Soil Research ◽  
1994 ◽  
Vol 32 (4) ◽  
pp. 781 ◽  
Author(s):  
BH Prasetyo ◽  
RJ Gilkes
Keyword(s):  
Iron Oxide ◽  
Iron Oxides ◽  
Crystal Size ◽  
Mean Value ◽  
Line Broadening ◽  
West Java ◽  
Volcanic Tuff ◽  
Red Soils ◽  
Al Substitution ◽  
Aluminium Substitution

The properties of iron oxide concentrates of Oxisols and Alfisols on volcanic tuff in West Java, Indonesia, were studied by XRD,TGA, TEM and chemical analysis.Goethite and hematite are the co-dominant iron oxides and are present in all samples. Iron content of the soils (dithionite-soluble Fe) ranges from 6.0 to 15.4%. Aluminium substitution in goethite and hematite ranges between 11 and 26 mol% and 0 and 9 mol% respectively. The Al substitution in hematite increases at about half the rate for goethite within the same samples. Crystal size of goethite and hematite was measured from line broadening of the 110 reflections and ranges between 7 and 18 nm for goethite with a mean value of 10 nm and between 7 and 28 nm for hematite with a mean value of 18 nm. The dehydroxylation temperature of goethite is in the range 290-320 �C and is linearly related to Al substitution by the equation y = 280 + 1.53x, (R(2) = 0.53). The goethite and hematite in these Indonesian soils are very similar to these minerals in tropical and Mediterranean soils from other regions.

The influence of pH on the synthesis of mixed Fe-Mn oxide minerals

Clay Minerals ◽  
1990 ◽  
Vol 25 (4) ◽  
pp. 507-518 ◽  
Author(s):  
M. H. Ebinger ◽  
D. G. Schulze
Keyword(s):  
Iron Oxides ◽  
Mole Fraction ◽  
Unit Cell ◽  
Mn Oxide ◽  
Cell Dimensions ◽  
The Mean ◽  
Mn Substitution ◽  
Oxide Minerals ◽  
Unit Cell Dimensions ◽  
Influence Of Ph

AbstractMn-substituted iron oxides were synthesized at pH 4, 6, 8, and 10 from Fe-Mn systems with Mn mole fractions (Mn/(Mn + Fe)) of 0, 0·2, 0·4, 0·6, 0·8, and 1·0, and kept at 50°C for 40 days. The Mn mole fraction in goethite was <0·07 at pH 4 but increased to ∼0.47 at pH 6. Goethite and/or hematite formed in Fe and Fe + Mn syntheses at pH 4 and pH 6 at Mn mole fractions ≤0·8, and at Mn mole fractions ≤0·2 at pH 8 and pH 10. Hausmannite and jacobsite formed at pH 8 and pH 10 at Mn mole fractions ≥0·4. In the pure Mn syntheses, manganite (γ-MnOOH) formed at pH 4 and pH 6, whereas hausmannite (Mn3O4) formed at pH 8 and pH 10. As the Mn substitution increased, the unit-cell dimensions of goethite shifted toward those of groutite, and the mean crystallite dimensions of goethite decreased.

Aluminium influence on iron oxides: XVIII. The effect of Al substitution and crystal size on magnetic hyperfine fields of natural goethites

Clay Minerals ◽  
1996 ◽  
Vol 31 (4) ◽  
pp. 455-464 ◽  
Author(s):  
J. Friedl ◽  
U. Schwertmann
Keyword(s):  
Iron Oxides ◽  
Room Temperature ◽  
Crystal Size ◽  
Tropical Soil ◽  
Iron Ores ◽  
Hyperfine Fields ◽  
Al Substitution ◽  
Subtropical Soils ◽  
Crystallization Conditions ◽  
The Mean

AbstractTwo sets of natural Al-substituted goethites from contrasting surface environments (24 tropical and subtropical soils vs. ten lake iron ores from Finland) were characterized by Mössbauer spectra obtained at room temperature and 4.2 K. A negative correlation between Bhf and Al substitution (R2 = 0.751) was found by combining the data of all the samples, which was slightly improved (R2 = 0.779) by taking the mean coherence length perpendicular to 111 (MCL111) into account. The effect of Al on lowering Bhf was, however, stronger for the tropical soil goethites than for those of the lake ores. This is parallelled by a corresponding difference in the unit-cell decrease per unit Al substitution. These differences are believed to result from the crystallization conditions in the two different environments.

Concentration of iron oxides from soil clays by 5 m NaOH treatment: the complete removal of sodalite and kaolin

Clay Minerals ◽  
1991 ◽  
Vol 26 (4) ◽  
pp. 463-472 ◽  
Author(s):  
Balwant Singh ◽  
R. J. Gilkes
Keyword(s):  
Iron Oxide ◽  
Iron Oxides ◽  
Crystal Size ◽  
Complete Removal ◽  
Complete Dissolution ◽  
Al Substitution ◽  
Soil Clays ◽  
Naoh Treatment ◽  
Very High

AbstractThe Kämpf & Schwertmann (1982) procedure for concentrating iron oxides in soil clays by dissolution of kaolin and gibbsite by boiling for 1 h in 5 m NaOH may not dissolve all kaolin, and also results in the precipitation of sodalite. For the complete dissolution of kaolin in kaolin-rich soil clays a boiling time of 2 h in 5 m NaOH was required. The large amounts of sodalite produced were not removed by the prescribed single wash in 0·5 m HCl. Oxalate soluble Al contents of iron oxide concentrates were sometimes very high and dithionite Fe contents were very low both in concentrates containing sodalite, and in those for which sodalite was not detected by XRD, but where a previously unsuspected amorphous sodalite-like phase may have been present. Complete removal of precipitated sodalite was achieved by two extractions with 0·5 m HCl at 25°C for 20 min. This modified procedure does not alter the Al-substitution and crystal size of goethite, hematite and maghemite as determined by XRD measurements.

Chemistry, optics, and crystal growth of milarite from Strzegom, Poland

1986 ◽  
Vol 50 (356) ◽  
pp. 271-277 ◽  
Author(s):  
J. Janeczek
Keyword(s):  
Outer Zone ◽  
Hexagonal Symmetry ◽  
Chemical Zoning ◽  
Al Substitution ◽  
Basal Section ◽  
Cell Dimensions ◽  
Infra Red ◽  
Bright Green ◽  
Unit Cell Dimensions ◽  
Pale Green

AbstractMilarite was found in a cavity of a small pegmatitic segregation in association with albite, stilpnomelane and chabazite. Hexagonal, well-shaped crystals of milarite up to 4 mm in length are transparent, pale green in colour, and show bright green cathodoluminescence. The refractive indices are: ω = 1.535, ε = 1.534(Na). D = 2.55 g cm−3. The unit cell dimensions are: a 10.418(4), c 13.817(7) Å, V 1298.7 Å3. Anomalous biaxial sectors and birefringent optical patterns are visible in basal section. 2V varies from 34° in the {0001} sector to 64° in {101} sector. OAP azimuths are related to the external hexagonal symmetry of the crystals. Microprobe analyses of sections perpendicular and parallel to the c-axis revealed a uniform distribution of alkalis, mainly K2O, whereas CaO and Al2O3 contents are slightly higher in prismatic and pyramidal sectors than in the basal sector, but no systematic chemical zoning can be distinguished. The Al2O3 content decreases in the outer zone of the crystal studied due to Be-Al substitution. The average ‘anhydrous’ chemical formula of the Strzegom milarite is: (K0.98Na0.01)Ca1.93Mn0.02(Be2.16Al0.93)(Si12O30). Infra-red data indicate the presence of H2O molecules in the milarite. Internal growth structures of the crystals indicate rhythmic fluctuations of the growth rate resulting in an internal strain, inducing anomalous optical patterns. HRTEM study did not reveal any significant distortion of the milarite lattice.

Variations in the properties of iron oxides within individual specimens of lateritic duricrust

Soil Research ◽  
1987 ◽  
Vol 25 (3) ◽  
pp. 287 ◽  
Author(s):  
RR Anand ◽  
RJ Gilkes
Keyword(s):  
Iron Oxides ◽  
Crystal Size ◽  
Al Substitution ◽  
History Of

The morphologically distinct materials in Darling Range lateritic duricrust (i.e. loose and cemented pisoliths, concretions, matrix, pisolith coatings and void coatings) exhibit goethite/(goethite + hematite) ratios ranging from 0.15 for individual pisoliths to 1.0 for void coatings. Mole % Al substitution ranged from 20 to 34% in goethite and from 2 to 15% in hematite. Goethite and hematite in pisoliths and concretions were mostly highly Al substituted. Al substitution in goethite was positively related (P < 0.01) to Al substitution in hematite. Al substitution in maghemite was less than 5%. Goethite crystals ranged in size from 130 to 260 A. Hematite crystals ranged from 140 to 520 A, and were systematically smaller in pisoliths. Crystal size of goethite and hematite decreased with increasing Al substitution. Hematite crystals were usually about 50% larger than goethite crystals in the same sample, and crystal sizes of goethite and hematite were positively correlated (P < 0.01). Goethite and hematite occurred as aggregates of subrounded platy crystals. Differences in the properties of goethite and hematite between morphologically distinct materials in single hand specimens are indicative of the complex history of these duricrusts.

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