Hematite In Soils Research Articles

A New Perspective on the Applicability of Diffuse Reflectance Spectroscopy for Determining the Hematite Content of Fe-Rich Soils in the Tropical Margins of China

Hematite and goethite are widely occurring chromogenic iron oxides in soils and sediments that are sensitive to climatic dry/wet shifts. However, only by accurately quantifying the content or ratio of hematite and goethite can they be applied reliably to palaeoclimate reconstruction. Compared to the Loess Plateau of China, hematite in the soils of southern China has not been sufficiently studied. We used diffuse reflectance spectroscopy (abbreviation DRS, including the first-derivative curves and the second-derivative curves of the Kubelka–Munk remission functions), combined with ignition at 950 °C, and X-ray fluorescence (XRF) to quantify the hematite content of four tropical-margin iron-rich soil profiles with different matrix compositions in the Leizhou Peninsula, China. We also examined the application of hematite quantification parameters in soils with different matrix compositions under the same climatic conditions. Our main findings are as follows: (i) DRS first-derivative curves can reflect the presence of goethite and hematite in soils, and their relative contents can be compared within the same profile. (ii) The second-derivative curve of the Kubelka–Munk remission functions can reflect the relative proportions of goethite and hematite and provide information about the degree of Al substitution. (iii) Combined with calibration equations, soil redness can reliably quantify the hematite content, but it is necessary to consider the effect of mucilage envelopes in the process of hematite formation. Additionally, we summarize various methods used for quantifying hematite, and the influence of soil matrix compositions, with the aim of providing a reference for hematite quantification elsewhere. We also propose a new indicator (ΔHmRed/HmRed) to help detect iron hydroxide/iron oxide changes in soils.

Effects of hematite on the stabilization of copper, cadmium and phosphorus in a contaminated red soil amended with hydroxyapatite.

Iron (Fe) oxides are intimately coupled with phosphorus and closely associated with the bioavailability of potential toxic elements (PTEs) in soil. Thus, Fe oxides may influence the stabilization of PTEs in contaminated soils amended by phosphorus. To evaluate the effects of hematite (HMT) on the stabilization of PTEs, 1-5% (by weight) of HMT was added into a contaminated red soil amended with hydroxyapatite (HAP) to simulate naturally occurring Fe oxides. The stabilization efficiencies of soil copper (Cu) and cadmium (Cd) amended with HAP in soils with low, moderate, and high content of HMT were assessed after a 60-day incubation. HAP treated the soil with high rate HMT decreased the CaCl2-extractable and acid-soluble fractions of Cu and Cd than that of HAP alone. In particular, CaCl2-extactable Cu and Cd in the soil with 5% HMT amended by HAP were 91-95% and 41-68% lower than those amended with only HAP. High content of HMT in soil could decrease the concentration of labile phosphorus in the presence of HAP, but it did not increase the concentration of NaOH-extractable inorganic phosphorus (the fraction bound to Fe oxides). The concentrations of free and crystalline Fe oxides were significantly increased by adding high dosages of HMT with or without HAP. High content of HMT in soil amended by HAP reduced metal phytotoxicity and uptake by wheat shoots than the soil containing HAP without HMT. The results indicate that HMT can promote Cu and Cd stabilization while decrease labile phosphorus in red soil amended with HAP, suggesting that phosphorus-based amendments combined with Fe oxides can be used to stabilize PTEs in contaminated red soils.

Mechanisms on the morphology variation of hematite crystals by Al substitution: The modification of Fe and O reticular densities.

Al substitution in hematite is ubiquitous in soils. With the increase of Al amount, the hematite morphology changes from rhombohedral crystals to disk-shaped ones, but the underlying mechanism is poorly understood. Herein, a series of Al-substituted hematite were synthesized and characterized by synchrotron X-ray diffraction (SXRD), field emission scanning electron microscopy (FESEM), high resolution electron transmission microscopy (HRTEM) and extended X-ray absorption fine structure (EXAFS) spectroscopy, to investigate the effects of Al3+ substitution on the hematite structure and morphology. EXAFS and Rietveld structural refinement analyses find an increase in face-sharing (along c axis) Fe-Me (Me = Al, Fe) distances, edge-sharing (in a-b plane) Fe-Me (Me = Al, Fe) distances, and O-O average distances. Moreover, the face-sharing Fe-Me distances and O-O distances along c axis increase more significantly. This indicates a more apparent decrease in the reticular densities of Fe and O along the direction of c axis, which facilitates faster crystal growth along c axis and results in the evolution of morphology of Al-substituted hematite to disk-shaped crystals. The above results provide new insights into the morphology changes and environmental geochemistry behaviors of Al-contained hematite in soils, and are benefit for the control of crystal morphologies during its application as environmentally-friendly materials.

Characterization of barren, granitic soils from the Nubian Desert (SW Egypt) by 57Fe Mössbauer spectroscopy

Abstract 57Fe Mössbauer spectroscopy - a versatile technique involving the recoil-free, resonant absorption and emission of nuclear gamma (γ) rays by the iron-57 isotope in natural iron in solids - has been used to provide quantitative information about the mineral host, occupation sites and oxidation states of iron atoms in geological samples. This technique has been applied to the bulk chemistry of a barren soil (Soil A) derived from an aluminous-type granite and another barren soil (Soil B) derived from a sodic-type granite located ~ 100 kilometers apart in the Nubian Deseit in the currently hyper arid south-west of Egypt and which exhibit distinct chemical and mineral differences. The analyses indicate different mineral hosts for the iron in these samples, namely, vermiculite-chlorite plus some hematite in Soil A and hematite and goethite plus minor aegirines in Soil B. Each soil has distinct intensities of oxidized iron (89% for Soil A and 100% for Soil B) and these differences reflect changes in soil sources and processes.

Iron oxides in tropical soils on various parent materials

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/Fedrange 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.

Environmental association of iron minerals and iron concentrations in soils close to an abandoned manganese mine – a multivariate analytical approach

Environmental association of iron (Fe) minerals and Fe concentrations in soils close to the Kgwakgwe Mn oxide ore abandoned mine, Botswana are investigated in this study. Four hundred soil samples were obtained from a 4 km 2 area close to the abandoned mine. The Fe minerals in the soil samples were identified by x-ray diffractometry and the Fe concentrations by atomic absorption spectrophotometry. Results were processed using the statistical package for social science (SPSS). Iron minerals namely hematite and goethite were found in soils from the study area but only hematite in soils from the control site. Also Fe concentrations in soils from the study area were significantly higher than those from the control site. The correlations depicted very weak associations of these parameters. Hematite contributed significantly in the formation of the five clusters, goethite's contribution was for three of the clusters, and Fe concentrations in soils were for two of the clusters. At Kgwakgwe, exposed surfaces of mine workings, ferruginous shale and country rocks through wind erosion release particulate air matter, rich in Fe into the atmosphere which are transported over short distances and deposited on soils. Through chemical alteration processes, hematite is hydrated to goethite and neomineralization of goethite from the ferruginous shale occurs in the surrounding soils. Journal of Applied Sciences and Environmental Management Vol. 10(1) 2006: 31-36

Determinação indireta do teor de hematita no solo a partir de dados de colorimetria e radiometria

A cor do solo é uma propriedade que deriva de alguns atributos do próprio solo, entre eles, do teor de óxidos de ferro. Desse modo, o estabelecimento de relações funcionais entre dados referentes à caracterização da cor e teores de óxidos de ferro apresenta-se como uma alternativa simples e rápida para a semiquantificação dos teores dos referidos óxidos. O objetivo do presente trabalho foi semiquantificar os teores de hematita na fração argila, em laboratório, a partir da avaliação automatizada das cores de amostras de solos do Estado de São Paulo, utilizando um colorímetro e um espectrorradiômetro. Os dados obtidos por radiometria serviram de base para a determinação da cor nos sistemas L*a*b* e Munsell, bem como para o cálculo de índices de avermelhamento (IAVs). Os IAVs apresentaram dependência funcional dos teores de hematita e foram as melhores relações verificadas com os índices determinados a partir de cores no sistema L*a*b*. Modelos exponenciais, baseados em dados obtidos por sensores, mostram-se adequados na predição dos teores de hematita.

Determination of Mean Crystallite Dimensions from X-Ray Diffraction Peak Profiles: A Comparative Analysis of Synthetic Hematites

AbstractX-ray diffraction (XRD) profile analysis of eight synthetic hematite samples was performed to identify the best parameters for determining the apparent mean crystallite dimension (D) and, consequently, surface area, The samples are comparable to soil hematite with respect to crystallinity. The procedure included: a) deconvolution of the XRD peaks to Gauss and Cauchy components and subtraction of the instrumental profile, b) determination of D from full-width at half-maximum, integral breadth, and integral breadth measurements of the Cauchy component, and c) comparison of deduced surface areas with those obtained by the N2-BET adsorption method. As expected, D values are strongly influenced by the broadening parameters. An appropriate selection of peaks is required to obtain size values along the crystallographic axes a (hkl: 110,300) and c (hkl: 104, 116) and to calculate reliable surface areas. Using the Cauchy component of the above peaks, the calculated surface areas compared well with those measured by the N2-BET adsorption method.

Multiple Iron-Rich Spinel Phases and Hematite in a Magnetic Soil Developing on Tuffite

A dusky red Latosol developing on tuffite was examined in detail in order to characterize its iron oxide mineralogy. Magnetic separation and selective chemical treatment were employed. The mineralogical analyses were carried out by powder X-ray diffraction and Mossbauer spectroscopy, with the electron microprobe technique being used to assess the chemical composition of selected grains. Results reveal that iron-rich spinel-structure phases from this pedosystem are rather variable in chemical composition and lattice parameters, and can be grouped in at least three major populations: the first group consisting of the iron-richest phase, with very low Ti and Cr and virtually no Mg content and high Al; the second group presenting Ti>Mg>>Al>Mn contents but no Cr and the third group related to the Mg-richest phase with Mg>Ti>>Al>Mn. Two major populations of hematite were also identified: one with ∼15 mol% Al and other practically Al-free. The first group is thought to be a product of neoformation in an Al-rich pedogenic medium whereas the second is likely to be transformed directly from maghemite. Though chemical treatment along with physical techniques provide a powerful way to characterize iron oxides of tropical soils, some methodological difficulties still remain, particularly those concerned with (i) the characterization and quantification of maghemite in presence of relatively large amount of hematite in the soil mixture, particularly by Mossbauer spectroscopy, and (ii) the allocation of the isomorphous substituents for iron in the cation sites of the spinel structure. Possible mechanisms of alteration of iron-rich phases in this pedosystem are discussed.

Goethite and Hematite Formation in the Presence of Clay Minerals and Gibbsite at 25°C

AbstractAfter 8.4 yr at 25 °C under water, ferrihydrite was almost completely converted into a mixture of goethite and hematite. In contrast, aging in the presence of various clay minerals and gibbsite retarded (kaolinite, illite, smectite, gibbsite) or even blocked (soil smectite, allophane) transformation. The conversion rate was inversely related to the final Si concentration in solution. In addition, the presence of clay minerals resulted in higher hematite to goethite ratios, lower mean crystallite dimensions for both oxides, and the incorporation of Al into the goethite and hematite structures. Similar effects have been observed for coexisting goethite and hematite in soils.

Mineralverwitterung, tonmineralbildung und rubefizierung in Terrae calcis der slowakei Ein beitrag zum paläoklimatischen aussagewert von kalkstein-Rotlehmen in Mitteleuropa

Mineralverwitterung, tonmineralbildung und rubefizierung in Terrae calcis der slowakei Ein beitrag zum paläoklimatischen aussagewert von kalkstein-Rotlehmen in Mitteleuropa

Mineralverwitterung, Tonmineralbildung Und Rubefizierung In Terrae Calcis Der Slowakei: Ein Beitrag Zum Paläoklimatischen Aussagewert Von Kalkstein-Rotlehmen In Mitteleuropa

Mineralverwitterung, Tonmineralbildung Und Rubefizierung In Terrae Calcis Der Slowakei: Ein Beitrag Zum Paläoklimatischen Aussagewert Von Kalkstein-Rotlehmen In Mitteleuropa

A swelling hematite/layer-silicate complex in weathered granite

AbstractA naturally occurring hematitic iron oxide/layer-silicate complex has been found in red mottled patches of a deeply weathered granite in north-east Scotland. X-ray diffraction shows a basal spacing of 36 Å—also observable by high resolution electron microscopy—which expands to 40 Å with glycerol and contracts to 33·5 Å on heating. Selected area electron diffraction reveals a composite hematite/layer-silicate pattern with the a-axis of hematite parallel to the b-axis of the silicate. The IR spectrum of the complex clearly shows the contribution made by each of the components. The silicate, with bands due to OH stretching at 3602 cm−1, OH deformation at 855 cm−1, and Si-O stretching at 1085, 1035, 540 and 471 cm−1 resembles ferruginous pyrophyllite, while the hematite, with a perpendicular band at 647 cm−1, in-plane bands at 519, 438, 400, 302 and 227 cm−1 and a characteristic pattern of relative band intensities, is similar to a platy form of soil hematite. Electron microprobe analysis of individual particles gives the complex an (Fe + Al): Si ratio of 6:1, which is consistent with a structure made up of twelve octahedral sheets terminated on both sides by a silicate sheet. It seems likely that the complex developed from a siliceous ferrihydrite which became progressively more organized with geological time.

Determination of allophane and amorphous inorganic matter in clay fraction of soils

Abstract The quantitative determination of allophane and amorphous inorganic matter in the clay fractions of volcanic ash soils was examined by means of five methods. An outline of the results is as follows: An alternate dissolution with 8 N HCl for 30 min and warmed 0.5 n NaOH for 5 min according to the method of Segalen (8) was suited for the purpose. The coexistence of gibbsite did not strongly influence the determination of allophane and amorphous matter, but goethite and hematite in soils behaved just as amorphous matter in this method. A method based on the weight loss with heating at 200°C, which is newly proposed in this study, was statistically analyzed in the clay fractions of soils and the allophane-halloysite mixture samples, compared with the result of the method by means of the alternate dissolution with HCI and NaOH. It was clarified that the method based on the weight loss with heating at 200°C could be applied to a determination of allophane and amorphous matter, i.e., a high linearcorrelation was established between the weight loss with heating and the contents of allophane and amorphous matter obtained from the alternate dissolution with HCl and NaOH. Three other methods; a dissolution with boiled 0.5 n NaOH for 2.5 min, an extraction with acid ammonium-oxalate solution, and cation-exchange capacity delta value of allophane. These were not so good as the two first mentioned above.