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Showing papers on "Goethite published in 1987"


Journal ArticleDOI
06 Nov 1987-Science
TL;DR: In this article, in situ extended x-ray absorption fine structure (EXAFS) measurements of adsorbed selenate and selenite ions at the α-FeOOH(goethite)-water interface have been performed; these measurements show that selenates forms a weakly bonded, outer-sphere complex and that Selenite forms a strongly bonded, inner-spheres complex.
Abstract: A novel application of x-ray absorption spectroscopy has provided structural information for ions sorbed at oxide-water interfaces. As an example, in situ extended x-ray absorption fine structure (EXAFS) measurements of adsorbed selenate and selenite ions at ah α-FeOOH(goethite)—water interface have been performed; these measurements show that selenate forms a weakly bonded, outer-sphere complex and that selenite forms a strongly bonded, inner-sphere complex. The selenite ion is bonded directly to the goethite surface in a bidentate fashion with two iron atoms 3.38 angstroms from the selenium atom. Adsorbed selenate has no iron atom in the second coordination shell of selenium, which indicates retention of its hydration sphere upon sorption. This method provides direct structural information for adsorbed species at solid-liquid interfaces.

477 citations



Journal ArticleDOI
TL;DR: In this article, the authors observed that the presence of silicate species modifies the morphology of both reaction products and showed that at high levels of silicates, goethite crystals adopt a pseudohexagonal shape.
Abstract: The transformation of ferrihydrite to goethite and/or hematite in alkaline media is strongly retarded by the presence of silicate species. These species probably stabilize ferrihydrite by adsorbing on the particles of ferrihydrite and linking them into an immobile network. At concentrations low enough for the transformation to proceed, silicate species promote the formation of hematite and hinder the nucleation of goethite. The presence of silicate species modifies the morphology of both reaction products. Hematite forms ellipsoidal single crystals, commonly displaying outgrowths of goethite. Silicate species in solution appear to enhance the development of the (021) faces of goethite, probably by preferential adsorption on these faces; at high levels of silicate species, goethite crystals adopt a pseudohexagonal habit. This morphology has not been observed previously for goethite.

225 citations


Journal ArticleDOI
TL;DR: In this article, a complete mechanism for the transformation of goethite to hematite based on the results of thermogravimetric, transmission electron microscope and X-ray diffraction investigations is presented.
Abstract: A complete mechanism for the transformation goethite to hematite based upon the results of thermogravimetric, transmission electron microscope and X-ray diffraction investigations is presented. A porous microstructure and hematite crystallites in twin orientation are found to develop during transformation. For the main part of the transformation, and at higher temperatures, the reaction is controlled by a two-dimensional phase boundary. Activation energies of 169 ± 8 kJ/mole (for an ore mineral) and 154 ± 15 kJ/mole (for a recent sedimentary goethite) were obtained for this part of the transformation. At early stages and lower temperatures, the mechanism is one of proton/iron transfer across the reaction interface. Important goethite characteristics are grain size, shape, crystallinity and excess water content. The activation energy is found to depend upon temperature and degree of dehydration.

145 citations


Journal ArticleDOI
TL;DR: In this paper, the reductive dissolution of Na-dithionite of 28 synthetic goethites and 26 hematites having widely different crystal morphologies, specific surfaces and aluminium substitution levels has been investigated.
Abstract: The reductive dissolution by Na-dithionite of 28 synthetic goethites and 26 hematites having widely different crystal morphologies, specific surfaces and aluminium substitution levels has been investigated. For both minerals the initial dissolution rate per unit of surface area decreased with aluminium substitution. At similar aluminium substitution and specific surface, goethites and hematites showed similar dissolution rates. These results suggest that preferential, reductive dissolution of hematite in some natural environments, such as soils or sediments, might be due to the generally lower aluminium substitution of this mineral compared to goethite.

130 citations


Journal ArticleDOI
TL;DR: In this paper, a photochemical dissolution of goethite in acid/oxalate solution, Fe3+, Fe2+, and CO2 were released and towards the end of the reaction ferrous oxalate precipitated.
Abstract: During photochemical dissolution of goethite in acid/oxalate solution, Fe3+, Fe2+, and CO2 were released and towards the end of the reaction ferrous oxalate precipitated. The dissolution process involved an initial slow stage followed by a much faster reaction. The slow stage was eliminated by addition of 20 ppm Fe2+ to the system at the start of the reaction. The presence of this Fe2+ did not accelerate the secondary dissolution process. Both protons and oxalate ions appear to have been involved in the dissolution process. Dissolution was accelerated by an increase in oxalate concentration (from 0.0025 to 0.025 M) in the system and also depended on pH, reaching a maximum rate at pH 2.6. Highly substituted (15.9 mole % Al) goethite dissolved more slowly per unit area than unsubstituted goethite. Lepidocrocite (γ-FeOOH) dissolved faster than goethite. The first stage of the dissolution process probably proceeded by slow release of Fe3+ through complexation with oxalate adsorbed on the goethite surface. The faster, secondary step appears to have been a reductive dissolution reaction involving adsorbed ferrous oxalate.

129 citations


Journal ArticleDOI
TL;DR: In the presence of Mn(II), ferrihydrite transforms into Mn-goethite and/or jacobsite, and, at high Mn(III) concentrations, a 7-A phyllomanganate as mentioned in this paper.
Abstract: In the presence of Mn(II), ferrihydrite transforms into Mn-goethite and/or jacobsite. Chemical analysis showed that as much as 15 mole % Mn replaced Fe in the goethite structure. If Mn(III) replaced Mn(II), the formation of jacobsite was suppressed; ferrihydrite transformed into Mn-goethite, and, at high Mn(III) concentrations, a 7-A phyllomanganate. Low levels of Mn(II) retarded the transformation of ferrihydrite only slightly, whereas in an Mn(III) system the nucleation and growth of Mn-goethite were both hindered. Mn-goethite nucleated in solution, whereas jacobsite appeared to form by interaction of dissolved Mn(II) species with ferrihydrite. Mn suppressed the formation of hematite in these systems; however, Mn-hematite containing as much as 5 mole % Mn was induced to form at pH 8 by adding oxalate to the system. Transmission electron micrographs showed that goethite crystals grown in the presence of Mn were long (≤2 μm) and thin and commonly contained etch pits. The presence of Mn appears to have promoted twinning.

118 citations


Journal ArticleDOI
TL;DR: In this paper, a plot of δD vs.δ18O values from a diverse group of natural goethites defines a data array which is approximately parallel to the meteoric water line.

112 citations


Journal ArticleDOI
TL;DR: In this article, field and laboratory studies were conducted to relate the mineralogy of rock and soil samples containing hematite, goethite, and jarosite to their reflectance properties in visible and near-infrared wavelengths.
Abstract: Field and laboratory studies were conducted to relate the mineralogy of rock and soil samples containing hematite (α-Fe2O3), goethite (α-FeOOH), and jarosite (KFe3(SO4)2(OH)6) to their reflectance properties in visible and near-infrared wavelengths. Field reflectance measurements of regolith containing one or more of these minerals were made in the Goldfield, Nevada, mining district with a four-channel radiometer. The mineralogy and reflectance properties of regolith samples collected from these field measurement sites were then determined by laboratory studies. Mossbauer spectroscopy was used to identify the iron minerals present and their relative proportions. The reflectance spectra of samples containing hematite and goethite were characterized by a reflectance minimum near 900 nm. The location of this minimum could be accounted for by the relative proportions of hematite and goethite present in the samples. Under certain conditions it may be feasible to estimate the relative proportions of hematite and goethite on the earth's surface by determining the location of this near-infrared reflectance minimum in high spectral resolution remote sensing data. In addition, the field measurements suggest that the ratio of band passes at 852 and 982 nm may be used to distinguish qualitatively among hematite, goethite, and jarosite. Thus maps of the distribution of these minerals may be derived from scanner images acquired in those band passes.

92 citations


Journal ArticleDOI
TL;DR: In this article, the adsorption of oxalic, phthalic, salicylic, and lactic acids on goethite from 0.53 M NaCl and from synthetic major ion sea water is examined to determine the effect of Mg, Ca, and SO/sub 4/ on the adsore behavior of the organic compounds.

82 citations


Journal ArticleDOI
TL;DR: In this article, the thermal decomposition of goethite is investigated at various temperatures between 25 and 700°C in vacuo and the micropores of uniform size (0.8 nm in width) are progressively opened in the course of decomposition reaction.

Journal ArticleDOI
TL;DR: The mode of Ge incorporation in these minerals was investigated by high-resolution K-edge fluorescence spectroscopy using synchrotron radiation as discussed by the authors, which showed that Ge substitutes for Fe in the octahedral metal sites of the studied hematite and goethite, with average Ge-ligand bond lengths of 1.88 A.

Journal ArticleDOI
TL;DR: X-ray photoelectron spectroscopy (XPS) was evaluated as a technique to study anion adsorption on soil minerals; in this case, the well-characterized systems of phosphate, sulfate, and selenite adaption on goethite (α-FeOOH) as discussed by the authors.
Abstract: X-ray photoelectron spectroscopy (XPS) was evaluated as a technique to study anion adsorption on soil minerals; in this case, the well-characterized systems of phosphate, sulfate, and selenite adsorption on goethite (α-FeOOH). X-ray photoelectron spectroscopy measured directly the surface coverage, the form of the adsorbed species and substrate, and the pH dependence of adsorption. The results confirm the previously reported adsorption mode in which two A-type hydroxyls are replaced by coordination of two of the oxygen atoms of the anion.

Journal ArticleDOI
TL;DR: In this article, 15 iron oxide accumulations from the bottoms of two Finnish lakes ("lake ores") were found to contain as much as 50% Fe. Differential X-ray powder diffraction and selective dissolution by oxalate showed that the samples consisted of poorly crystallized goethite and ferrihydrite.
Abstract: Fifteen iron oxide accumulations from the bottoms of two Finnish lakes ("lake ores") were found to contain as much as 50% Fe. Differential X-ray powder diffraction and selective dissolution by oxalate showed that the samples consisted of poorly crystallized goethite and ferrihydrite. The crust ores of one lake had higher ferrihydrite to goethite ratios than the nodular ores of the other lake. The higher ferrihydrite proportion was attributed to a higher rate of Fe 2+ supply from the ground water and/or a higher rate of oxidation as a function of water depth and bottom-sediment permeability. Values of Al-for-Fe substitution of the goethites determined from unit-cell dimensions agreed with those obtained from chemical extraction if the unit-cell volume rather than the c dimension was used. In very small goethite crystals a slight expansion of the a unit-cell dimension is probaby compensated by a corresponding contraction of the c dimension, so that a contraction of the c dimension need not necessarily be caused by AI substitution. The goethites of the two lakes differed significantly in their Al-for-Fe substitutions and hence in their unit-cell sizes, OH-bending characteristics, dehydroxylation temperatures, dissolution kinetics, and MSss- bauer parameters. The difference in Al substitution (0 vs. 7 mole %) is attributed to the Al-supplying power of the bottom sediments: the silty-clayey sediments in one lake appear to have supplied A1 during goethite formation, whereas the gravelly-sandy sediments in the other lake did not. The compositions of the goethites thus reflect their environments of formation.

Journal ArticleDOI
TL;DR: Goethite and haematite were most abundant in iron oxides derived from dolerite, but were not preferentially associated with goethite or hahematite as discussed by the authors.
Abstract: SUMMARY Lateritic soils developed from dolerite contained larger amounts of goethite and haematite than those developed from granite. The goethite/(goethite + haematite) ratio in granitic soils ranged from 0.55 to 1 and from 0.29 to 0.83 in doleritic soils. Maghemite ranged in abundance from 0 to 10% and it only occurred in duricrust. Mole % Al substitution ranged from 16 to 33% in goethite and from 2.5 to 10% in haematite and was similar for both granitic and doleritic soils. Al substitution in maghemite was <5%. A significant, positive correlation (P<0.01) occurred between Al substitution in goethite and the amount of gibbsite in the soil. The dehydroxylation temperature of goethite ranged from 292 to 334°C and was positively correlated with the mole % Al substitution. Goethite crystals varied in size from 16 to 26 nm and haematite crystals from 18 to 59 nm. Goethite and haematite crystals occurred as aggregates of subrounded platy crystals. Iron oxides obtained by NaOH treatment contained much of the minor element contents of the soils; mean concentrations (μg g−1) were: Zn 19.9, Cu 31, Mn 68, Ni 140, Co 32, Cr 394 and V 696. These minor elements were most abundant in iron oxides derived from dolerite, but were not preferentially associated with goethite or haematite.

Journal ArticleDOI
01 Dec 1987-Catena
TL;DR: In this article, a soil toposequence in NE Italy was studied, which consists of a terra rossa on Cretaceous limestone on the upper slope grading downwards into a colluvial fan with terra rssa material and finally into alluvial river sediments.
Abstract: A soil toposequence in NE Italy was studied, which consists of a terra rossa on Cretaceous limestone on the upper slope grading downwards into a colluvial fan with terra rossa material and finally into alluvial river sediments. It is postulated that the red colluviated terra rossa material has come under a moister hydroregime which provided reducing conditions. Because hematite of the terra rossa dissolved preferentially over goethite, as shown by quantitative Fe oxide mineralogy, soil color changed from 2.5YR to 7.5YR. The soils contained two types of concretions, red ones with a low Feo/Fed ratio and a high content of hematite and low content of Mn-oxides and black ones with a high Feo/Fed ratio, a small amount of hematite and abundant Mn oxides. The red concretions are therefore considered as inherited from an earlier period of pedogenesis whereas the black ones are neoformed in the present pedoenvironment. This is further supported by the lower Al-for-Fe substitution of goethite in the black concretions as compared to a higher Al substitution in the goethite inherited from the terra rossa.

Journal ArticleDOI
TL;DR: In this article, X-ray diffraction (XRD) indicated that the Fe-rich precipitates consist mainly of a poorly ordered ferrihydrite (5 Fe 2 O 3 · 9 H 2 O).

Journal ArticleDOI
TL;DR: A tentative calibration of CO2 isobars for the above reaction has been attempted using measured trapped CO2 and isotopic temperature data for a natural goethite from a documented marine environment, as well as information obtained from the literature as discussed by the authors.

Journal ArticleDOI
TL;DR: In this article, the properties of goethite and hematite in the Darling Range lateritic duricrusts were investigated and the results indicated that the properties differ significantly between morphologically distinct materials in single hand specimens.
Abstract: The morphologically distinct materials in Darling Range lateritic duricrust (ie loose and cemented pisoliths, concretions, matrix, pisolith coatings and void coatings) exhibit goethite/(goethite + hematite) ratios ranging from 015 for individual pisoliths to 10 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 < 001) 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 < 001) 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

Journal ArticleDOI
TL;DR: In the presence of 9.6 mol% silicate species, goethite (α-FeOOH) grows from ferrihydrite (5Fe2O3·9H2O) at pH 12.5 as a mixture of pseudohexagonal plates and bipyramids.
Abstract: In the presence of 9.6 mol% silicate species, goethite (α-FeOOH) grows from ferrihydrite (5Fe2O3·9H2O) at pH 12.5 as a mixture of pseudohexagonal plates and bipyramids, whereas in the absence of silicate species, acicular crystals of goethite are formed.

Journal ArticleDOI
TL;DR: In this paper, the reduction of oxygen and hydrogen peroxide (H2O2) into hydroxyl radicals by selected iron compounds in a phosphate buffered solution was studied.
Abstract: The deleterious effects of radicals in biological systems are now admitted. The aim of the present work was to study the reduction of oxygen and hydrogen peroxide (H2O2) into hydroxyl radicals by selected iron compounds in a phosphate buffered solution. Radical detection has been carried out by electron spin resonance spectroscopy (ESR) with “spin trapping”; (5,5‐dimethyl‐1‐pyrroline N‐oxide, DMPO). The following minerals have been used: goethite (FeOOH a), akaganeite (FeOOH β), hematite Fe2O3α), magnetite (Fe3O4), siderite (FeCO3), and crocidolite fibres (Na2Fe3Si8O22(OH)2). Crocidolite and siderite reduced O2 into OH∗. Catalase inhibited this reduction. The reduction occurs at the mineral surface. When H2O2 was added to the buffer solution, goethite was inactive, akaganeite, magnetite, crocidolite and hematite were active and siderite was very active. These reactions could play a role in the mechanisms of toxic injury caused by some solid iron compounds.

Journal ArticleDOI
TL;DR: The influence of a recent forest fire on the iron oxide phases, present in the A and B horizon of a brown earth from Corsica, was examined by X-ray diffraction and chemical analysis.
Abstract: The influence of a recent forest fire on the iron oxide phases, present in the A and the B horizon of a brown earth from Corsica, was examined by X-ray diffraction and chemical analysis. In the B horizon goethite and lepidocrocite, in the A horizon maghemite and hematite were identified. From the Al/(Al+Fe) ratio, which was determined for all four minerals by XRD, it was concluded that goethite was the precursor of hematite and lepidocrocite the precursor of maghemite respectively. The proportion of maghemite formed in the A horizon was calculated from the difference in Fed between the untreated sample and that free of maghemite. Because of substantial dissolution of clay minerals even after 5 citrate-bicarbonate treatments, it was not possible to determine Ald correctly.

Book ChapterDOI
01 Jan 1987
TL;DR: In this article, the role of Fe(OH)3 in removal of the last traces of dissolved iron and in the elimination of objectionable impurities, such as germanium in zinc circuits, is discussed.
Abstract: Iron is commonly eliminated from hydrometallurgical process streams by oxidation to Fe3+, followed by hydrolysis–precipitation of a filterable iron compound. Current practice focusses on the precipitation of four species: iron hydroxide, the jarosites, FeO.OH and hematite. Although the precipitation of ferric hydroxide normally is avoided because of its poor filtration properties, the key role of Fe(OH)3 in the removal of the last traces of dissolved iron and in the elimination of objectionable impurities, such as germanium in zinc circuits, is discussed. The precipitation of jarosite–type compounds is widely used to reject iron and sulphate in a readily filterable form, and new applications of this technology are reviewed. The ability of jarosites to incorporate impurities such as silver or arsenic is discussed. The precipitation of α FeO.OH (goethite) in sulphate media requires that the concentration of Fe3+ be

Journal ArticleDOI
TL;DR: In this paper, the influence of Birnessite (δ-MnO2) on the precipitation products of iron was studied, in the FeCl2-NH4OH system at different Mn/Fe molar ratios (0, 0.1 and 1.0), by X-ray, TEM, IR and chemical analyses.
Abstract: The influence of birnessite (δ-MnO2) on the precipitation products of iron was studied, in the FeCl2-NH4OH system at different Mn/Fe molar ratios (0, 0.01, 0.1 and 1.0) and in the acidic pH (4.0, 5.0 and 6.0) range, by X-ray, TEM, IR and chemical analyses. The precipitation products formed at pH 5.0 and 6.0 were found to be lepidocrocite (γ-FeOOH) in the absence of birnessite. Birnessite promoted increased precipitation of Fe oxide; the oxidation of Fe(II) by MnO2 was thermodynamically feasible and was confirmed by the presence of Mn(II) in the solution by ESR data. Birnessite also influenced the crystallization processes of hydrolytic products of Fe which range from lepidocrocite through goethite (α-FeOOH), akaganeite (β-FeOOH), to X-ray noncrystalline Fe oxides. The noncrystalline Fe oxides formed at a Mn/Fe molar ratio of 1.0 were characterized by infrared absorption maxima at 1400 and 750 cm−1. Key words: Birnessite, Fe(II) oxidation, ESR, lepidocrocite, akaganeite, noncrystalline oxide

Journal ArticleDOI
TL;DR: In this paper, the conditional standard potentials of iron oxides with hydrogen were calculated using the formula Eo (volt) = Eh + 0.059 lg(Fe2+)+ 0.18 pH which indicate the stability of Fe oxides against reduction.
Abstract: Partial reduction of iron(III) oxides with hydrogen in the presence of a platinum catalyst leads to an equilibrium state after 4–20 h. From the measured Eh, pH, and Fe2+ concentration conditional standard potentials can be calculated using the formula Eo (volt) = Eh + 0.059 lg(Fe2+) + 0.18 pH which indicate the stability of Fe oxides against reduction. The reduceability decreases following the order ferrihydrite > lepidocrocite > hematite > goethite. The difference between hematite and goethite was more pronounced than that predicted from thermodynamic data.


Journal ArticleDOI
TL;DR: In this paper, the authors show that fine iron particles having coercivity higher than 2000 Oe were produced by the conventional method which is conmercially used, i.e., the reduction of acicular goethite particles with hydrogen gas.
Abstract: Fine iron particles having coercivity higher than 2000 Oe were produced by the conventional method which is conmercially used,i.e, the reduction of acicular goethite particles with hydrogen gas. This could be done by adsorption of Nd3+or Ce3+ions together with B3+ions on the surface of the goethite particles. Electron micrographs show that the particles have very smooth surface and few micropores, and are isolated from each other. The optimum size of the iron particles is around 0.13 μm in length and 0.02 μm in width. The specific surface area of this powder is about 38 m2/g, which is much lower than the ordinary ones. This super high coercivity may be due to the peculiar microstructure of the amorphous iron oxide layer which is coupled with the iron core, together with the well defined single domain behavior of the iron particles.

Journal ArticleDOI
TL;DR: In this article, the authors investigated changes in the dissolution of North Carolina phosphate rock and NaHCO3-soluble P arising from the addition of goethite (a-FeOOH) to soil.
Abstract: This laboratory experiment investigated changes in the dissolution of North Carolina phosphate rock and NaHCO3-soluble P arising from the addition of goethite (a-FeOOH) to soil. Increasing goethite in the soil increased the amount of phosphate rock (PR) dissolution as measured by the increase in exchangeable Ca (ACa) values. Increased dissolution was, however, associated with decreased NaHCO3- soluble P due to P retention by goethite. The proportion of P dissolved from PR that was soluble in 0.5 M NaHCO3 solution decreased with contact period and with increased goethite. The increase in exchangeable Ca (ACa) was a better indicator of the extent of PR dissolution in goethite-containing soils than NaHCO3-soluble P.


Journal ArticleDOI
TL;DR: In this paper, an "induced hydrolysis" of exchangeable Al ions in the presence of variable charge materials at high salt concentrations was proposed, where the amount of monomeric, therefore extractable, Al as a function of the goethite content in the 1 M KCI-montmorillonite-goethite mixtures was calculated.
Abstract: To explain why soils rich in variable charge materials often lack 1 M KCI-extractable Al ions, I proposed a mechanism, an “induced hydrolysis” of exchangeable Al ions in the presence of variable charge materials at high salt concentrations. I extracted exchangeable Al from mixtures of a montmorillonite saturated with Al and a synthetic goethite using a 1 M KCI solution. The amount of the extractable Al (per unit weight of the montmorillonite) decreased with increasing proportion of the goethite in the mixtures. I interpreted this experimental result as supporting the proposed mechanism, i.e., H+ released in the hydrolysis of Al is adsorbed on the goethite in a concentrated KCI solution and this removal of H+ induces further hydrolysis, resulting in the polymerization or precipitation of Al as hydroxides. I calculated the amount of monomeric, therefore extractable, Al as a function of the goethite content in the 1 M KCI-montmorillonite-goethite mixtures. The calculated amounts agreed well with the experime...