Goethite Crystals Research Articles

磁性材料の化学 ゲータイトの結晶学的モルフォロジー制御

The crystallographical and morphological properties of goethite particles in the course of oxidation in the strong alkaline solution was studied from X-ray diffraction analysis under the systematically controlled synthesizing conditions. The crystallite size ratio, D010D110, was changed by excess alkali content and oxidation conditions. The particle morphology of goethite depends on the relative growth rates of each faces of goethite crystals. From the SEM observation, the vertical and horizontal axes of goethite are proposed to be (110) and the lateral growth is assumed to be occurred along (110) easily because of the topotaxy between Fe(OH)2 and goethite. It is concluded that the crystallite size ratio depends on the development of (110) face during crystal growth, which in turn, is related to the ferrous complex (FeOH+) content.

Dehydroxylation of Aluminous Goethite: Unit Cell Dimensions, Crystal Size and Surface Area

AbstractThis work investigates unit cell dimensions, crystal size and specific surface area of aluminous goethite that was progressively dehydroxylated to form hematite. Goethite synthesized from the ferrous system altered to hematite with DTGA maximum increasing from 236° to 273°C for 0 to 30.1 mole % Al-substitution. Unit cell dimensions of goethite and hematite decreased as Al-substitution increased and increased as excess OH increased. The crystallographically equivalent a axis of goethite and c axis of hematite were more sensitive than other axes to the presence of excess structural OH associated with Al-substitution. Specific surface area increased from 147 to 288 m2/g for goethite and from 171 to 230 m2/g for hematite as Al-substitution increased. An increase in specific surface area on heating goethite at temperatures between 200° and 240°C is related to a decrease in the size of coherently diffracting domains of goethite crystals and to the development of pore and structural defects associated with the formation of hematite. The decrease in specific surface area for heating temperatures above 240°C is attributed to the growth of hematite crystals by diffusion.

The Use of Color to Quantify the Effects of pH and Temperature on the Crystallization Kinetics of Goethite under Highly Alkaline Conditions

AbstractThe crystallization kinetics of goethite were studied colorimetrically under highly alkaline conditions (pH 10.1–12.2) at temperatures from 40° to 85°C. Color changes during crystallization from fresh precipitates, plotted on a*-b* colorimetric diagrams, were used to discriminate between pure goethite and mixtures of goethite and hematite. Only the b* value increased as goethite crystallization proceeded, and even a minor increase in the a* value revealed the existence of hematite. The rate of goethite crystallization, estimated from the b* value, could be modeled by a pseudo-first-order rate law. This rate depended both on pH and on temperature. Apparent activation energies for the reactions of 56.1 kJ/mol at pH 11.7 and 48.2 kJ/mol at pH 12.2 were estimated from Arrhenius plots.

Phosphate sorption as related to mineralogy of a hydrosequence of soils from the Cerrado region (Brazil)

Phosphate sorption by minerals having surface FeOH or AlOH groups is an important process in highly weathered tropical soils. In this study, P sorption in 12 samples of soils of a typical hydrosequence of the Cerrado region (Brazil) was predicted by means of combining data on: (1) the amount and properties of gibbsite, goethite, hematite and kaolinite, and (2) the P-sorption characteristics of these minerals, according to existing data in the literature. The concentration, crystal morphology and surface area of these four minerals were studied by X-ray diffraction (XRD), thermogravimetry, transmission electron microscopy (TEM) and N 2-adsorption. Gibbsite crystals were subrounded with its longest axis between 50 and 100 nm. Kaolinite platelets had a diameter of 40–200 nm and frequently had euhedral faces. According to XRD data, the mean crystallite dimension (MCD) perpendicular to the (110) plane of goethite was about 30 nm; hematite crystals appeared to be platy (i.e., MCD 110 > MCD 104) and slightly larger than the goethite crystals. For most samples, the P sorption, measured at an equilibrium concentration of 10 −5M, was markedly lower than P sorption obtained by the sum of the sorptions estimated for each of the four minerals. The difference between measured and predicted P sorption became smaller when the soils were treated with H 2O 2. Moreover, the increase in P sorption with this treatment was positively correlated with the organic matter content. These results suggest that organic compounds, by probably competing for sorption sites, can substantially hinder P sorption of tropical soils. For soils low in organic matter, P sorption can be reasonably well predicted through the mineralogical characteristics of the soil.

Color Variations Associated with Rapid Formation of Goethite from Proto-Ferrihydrite at pH 13 and 40°C

AbstractColor variations from brown to yellow of synthesized goethite have been studied colorimetrically and spectroscopically. Goethite with various colors was synthesized at pH 13 and 40°C by varying the incubation time. Colorimetry revealed that the b* value (yellowish chroma) in L*a*b* color space was a quantitative indicator of color variations of the diluted samples. From UV-VIS-NIR spectra, the increase in the b* value was found to be caused by the increase in crystal field absorptions due to goethite formation around 500 nm. The b* value was a good indicator of the relative proportion of goethite in the precipitates including ferrihydrite. X-ray diffraction patterns and infrared spectra revealed that crystallization of goethite was associated with loss of water from the proto-ferrihydrite.

Bioprocessing of refractory oxide ores by bioreduction: Extraction of silver, molybdenum, and copper

Although much research has been conducted in the area of biooxidation of sulfide ores, few investigations in the bioreduction of oxide ores have been published. We report high recoveries of silver, molybdenum, and copper from refractory oxide ores through bioreduction. Metal-reducing Bacilli solubilize manganese and iron. Crystals of pyrolusite, goethite, and hematite are bacterially dissolved and entrapped target metal ions are released. Zinc and copper are solubilized by metabolic end products such as organic acids. Bioreductive leaching of oxide ores was more successful than chemical leaching. A 0.1% cyanide bottle roll on an Arizona manganiferous silver ore resulted in 13.7% silver extraction. Bioreductive leaching extracted 86% of the silver into the growth medium. Also, 99.8% of the manganese, >2;99% of the copper, and 91% of the zinc were solubilized. A cyanide bottle roll of the bioleached solids extracted an additional 8.5% of the silver for a total recovery of 94.5%. A 5% sulfuric acid bottle roll of a Nevada iron oxide molybdenum ore recovered 1.8% of the moly. Bioreduction solubilized 93% of the molybdenum into the growth medium. A follow-up acid bottle roll recovered no additional moly. Bioreductive leaching can be used to recover target metals from refractory oxide ores without the use of cyanide or sulfuric acid.

Crystallization of hematite and goethite in the presence of soil minerals

Freshly precipitated ferrihydrite 5Fe 2 O 3 -9H 2 O was stored at pH 7 and 40 ° C alone and in the presence of muscovite, kaolinite, quartz, gibbsite and soil clay at various mg mineral per mole Fe ratios (20, 200 and 500). The crystallization of ferrihydrite into hematite and geothite was monitored after 20, 50, 100, 148 and 210 days using Fe o /Fe d ratios and XRD. After 210 days, the ferrihydrite suspension free of soil minerals was nearly completely (Fe o /Fe d =0.10) converted into a mixture of goethite and hematite. The following materials retarded the crystallization of the iron oxides : deferrated soil clay>kaolinite>gibbsite>quartz. On the contrary, muscovite seems to promote the crystallization and induce a faster transformation of ferrihydrite into geothite and hematite. Also, the soil mineral/Fe ratio influences the crystallization of the iron oxides. The best differentiation between the studied minerals is observed when the soil mineral is 200 mg per mole Fe. At 40 ° C and pH 7, all soil minerals, except the soil clay, induce the preferential crystallization of hematite hematite plates, also with 120 ° oriented goethite needles, were observed in the presence of muscovite, suggesting a strong template effect

Influence of periatlantic climates and paleoclimates on the distribution and mineralogical composition of bauxites and ferricretes

Published (U-Th)/He ages indicate that an oolitic Miocene channel iron deposit (CID) on Mesa J in the Hamersley province of Western Australia (∼22 °S latitude) contains three predominant generations of Fe (III) oxides – two generations of older hematite and one of younger goethite. Selective dissolution and sequential atom balance calculations were combined with chemical and oxygen isotope analyses to determine the δ18O values of hematite, goethite, and quartz in eight samples from a core drilled in that CID. For the quartz (Q), δ18OQ = +21.7(±0.9)‰. For the younger hematite (Hm1), δ18OHm1 ≥ +3.6(±0.6)‰, whereas for the older hematite (Hm2), δ18OHm2 ≤ +2.1(±0.8)‰. The oolitic CID goethite (G) crystallized in the late Miocene [7(±1) Ma] and is a solid solution represented as Fe(1−Y)AlY(CO3)XO(1−X)OH with values of δ18OG that range from −0.4‰ to +0.7‰. A mixing model for the solid solution expresses the value of δ18OG in terms of Y, X, relevant fractionation factors, and the δ18O of the endmember FeOOH (δ18Ogt). Mixing model-derived values of δ18Ogt range from −2.4‰ to −0.7‰.Paired values of δDgt and δ18Ogt in seven of eight late Miocene oolitic goethites from Mesa J indicate crystallization from meteoric waters at an average temperature of 20(±5) °C. In the late Miocene, Mesa J was in the subtropics at a paleolatitude of ∼29 °S, which invites comparison with the climate of the near-coastal community of Mingenew in Western Australia (presently at 29 °S latitude). The modern MAT at Mingenew is 20 °C – i.e., indistinguishable from the late Miocene Mesa J average of 20 °C. However, this similarity is not matched by the mean annual precipitation (MAP). The modern MAP at Mingenew is about 400 mm, but the lateritic weathering that produces abundant pedogenic Fe (III) oxides appears to require a seasonally contrasting climate with rainfall totals of at least 1300 mm/yr. In the late Miocene, southward-shifted summer season tropical cyclones might have delivered such large amounts of rain (with relatively low δD and δ18O values). If so, the δDgt and δ18Ogt of the oolitic goethites of Mesa J support the idea of a rainfall-driven, possibly microbially mediated, summer season bias in the timing of crystallization. Thermal buffering in the regolith can reconcile summer-dominated goethite crystallization with a temperature that would be analytically indistinguishable from the MAT. Comparison of the δ18Ogt values of the Mesa J goethites with published δ18O values of goethites of similar age from two other sites in the Hamersley province suggest a possible increase in δ18O of late Miocene rainfall with increasing distance from the coast.

Iron mineralization in the radula teeth of the chiton Acanthopleura hirtosa

The structure, morphology and organization of the radula teeth of the chiton Acanthopleura hirtosa , together with their surrounding superior epithelium tissue, have been examined by using transmission electron microscopy and electron diffraction. Considerable amounts of iron are first seen in inclusions resembling ferritin aggregates and haemosiderin within the cells of the superior epithelium just before the onset of tooth-cusp mineralization. Iron appears to be delivered to the mineralizing surface of the cusp (presumably as Fe II ) via a series of microvilli, which extend out from the cells of the superior epithelium and which are contiguous with the surface of the tooth cusp. Before mineralization, the tooth cusp consists of a series of fine organic fibrils arranged perpendicular to the posterior edge but parallel to the anterior edge of the cusp. Mineralization within the cusp begins with the deposition of small spherules of ferrihydrite, which appear to have a close spatial relation to the organic matrix. Depending on their location within the cusp these spherules are rapidly replaced by crystals of either goethite, lepidocrocite and/or magnetite as mineralization proceeds. Mineralization is preferentially concentrated towards the posterior surface of the tooth cusp with a greater deposition of magnetite than is found on the anterior surface. We suggest that the initial control of mineralization in the tooth cusp is mediated by the organic matrix. However, the phase transformations among the several mineral phases found in the cusp may well be due to differential competition among reactions leading to these phases and this, in turn, may be controlled by the generation of differential redox and related potentials within the cusp.

Structural and material design of mature mineralized radula teeth of Patella vulgata (gastropoda)

The molluscan radula is a cutting apparatus employed in feeding. It is a toothed ribbon located in the mouth cavity. This study focuses on the characterization, organization, and hardness of the various components in full grown, mineralized, radula teeth of the common limpet Patella vulgata. Three major components are identified: Fibrous organic material, acicular crystals of goethite (α-FeOOH), and silica (SiO 2). Each forms a coherent network intertwined with the other two. The goethite crystals lie parallel to the fibers in the organic framework. The orientations of fibers and crystals are described in detail. The hardness of the leading part, i.e., the part that leads in the cutting direction, is about twice the hardness in the trailing part. It is argued that this difference results from the greater compactness of the mineral matter in the leading part. The function of the tooth as a cutting device is discussed on the basis of the data presented in this study.

Formation of goethite from ferrihydrite at physiological pH under the influence of cysteine

The presence of d-cysteine at L-cysteine: Fe ratios > 0.2 causes ferrihydrite (5Fe 2O 3·9H 2O) to transform rapidly to goethite [α-FeO(OH)] in the pH range 7.5–9 and at temperatures between 25–70°C. L-Cysteine is the first example of an organic ligand that directly promotes the formation of goethite; all organic ligands studied previously, suppressed the transformation of ferrihydrite to goethite. L-Cysteine is a reducing ligand which exhibits associative interactions with interfacial iron sites of ferrihydrite. It appears to act by converting these sites to more labile sites thus facilitating the transformation to goethite, possibly in conjuction with enhanced dissolution of ferrihydrite. The presence of phosphate or silicate species stabilized ferrihydrite and reduced the goethite promoting effect of cysteine. The implications of these results for biomineralization of iron oxides is considered. It is suggested that the crystals of goethite found in the teeth of limpets ( Patella vulgata) may have formed via activated reorganization of ferrihydrite, rather than by oxidatively induced hydrolysis of a ferrous precursor.

Direct Observation of Phosphate Precipitation in the Goethite/Phosphate System

AbstractA combined scanning Auger, XPS, scanning SIMS, and TEM (electron diffraction) investigation of naturally‐occurring goethite surfaces in contact with 10−3 M KH2PO4 solution for 90 d at 60 °C has shown that isolated crystallites of the mineral griphite, Fe3Mn2(PO4)2.5(OH)2, are formed by reprecipitation from solution. No adsorbed phosphate can be detected on the goethite surface above 0.1 atomic % and there is no phosphate penetration of the goethite crystals. Evidence concerning initial adsorption of phosphate, before recrystallization, is reconsidered. The results suggest that phosphate retention in Fe oxide systems may be due primarily to precipitation rather than adsorption.

Iron oxides in lateritic soils from Western Australia

SUMMARYLateritic 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.

Weathering of Basalt: Formation of Iddingsite

AbstractThe formation of iddingsite by the oxidative weathering of Fo80 olivine begins by solution of Mg from planar fissures, 20 Å wide and spaced 200 Å apart, parallel to (001). Oxidation of Fe within the remaining olivine provides nuclei for the topotactic growth of goethite. Cleavage cracks < 50 Å in diameter allow Na, Al, and Ca from adjacent minerals, particularly plagioclase, to enter the altering olivine while Mg and Si diffuse away. In the early stages of weathering, strips of Fe-rich smectite (saponite), 20–50 Å wide and 1–7 layers thick, form bridges 50–100 Å long across the planar fissures. Dioctahedral smectite crystallizes on the margins of wider cleavage-controlled fissures; with further weathering halloysite is formed away from the fissure walls. In the ultimate stages of alteration, the saponite and dioctahedral smectite are lost, leaving a porous, oriented aggregate of goethite crystals each measuring about 50 × 100 × 200 Å (X, Y, Z, respectively), with sporadic veins of halloysite crossing the pseudomorph.

Properties of Iron Oxides in Two Finnish Lakes in Relation to the Environment of Their Formation

AbstractFifteen 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 Fe2+ 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 Al 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 Möss-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 Al 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.

Effect of Manganese on the Transformation of Ferrihydrite into Goethite and Jacobsite in Alkaline Media

AbstractIn 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-Å 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.

Effect of Silicate Species on the Transformation of Ferrihydrite into Goethite and Hematite in Alkaline Media

AbstractThe 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.

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

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.

The influence of silicate species on the morphology of goethite (α-FeOOH) grown from ferrihydrite (5Fe2O3·9H2O)

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.

Factors That Govern the Formation of Multi-Domainic Goethites

AbstractTransmission electron microscopic (TEM) examination has shown that multi-domainic crystals of synthetic goethite consist of almost parallel intergrowths, each of which is slightly misoriented with respect to its neighbors. These intergrowths emanate from a central nucleus within the crystal. They can nucleate along both the x and y crystal axes, but subsequent growth is mainly in the z direction.The formation of multi-domainic goethites from ferrihydrite was favored by high pH (≥ 13) and, at lower pHs, by the addition of NaNO3 to the system. Decreasing the temperature of synthesis from 70° to 20°C also enhanced domain formation. The nucléation of domains was confined to the initial stage of goethite formation. Domains probably formed when crystal growth was very rapid or when adsorbed species blocked the appropriate sites on the nucleus material.