Showing papers on "Goethite published in 1983"

Effect of pH on the formation of goethite and hematite from ferrihydrite

Abstract: Storage of ferrihydrite in aqueous suspensions at 24°C and pHs between 2.5 and 12 for as long as three years resulted in the formation of goethite and hematite. The proportions and crystallinity of these products varied widely with the pH. Maximum hematite was formed between pH 7 and 8, and maximum goethite at pH 4 and at pH 12. The crystallinity of both products, as indicated by X-ray powder diffraction line broadening and magnetic hyperfine field values and distribution widths, was poorer, the lower the proportion of the corresponding product in the mixture. The existence of two competitive formation processes is suggested: goethite is formed via solution, preferably from monovalent Fe(III) ions [Fe(OH)2+ and Fe(OH)4−], and hematite by internal rearrangement and dehydration within the ferrihydrite aggregates. This concept relates the proportions of goethite and hematite to the activity of the Fe(III) ion species in solution, and implies that conditions favorable for the formation of goethite are unfavorable for that of hematite and vice versa.

The nature of soil particles particularly those reacting with arsenate in a series of chemically treated samples

Abstract: Arsenate uptake by a surface sample of a lateritic podzol was controlled mainly by iron oxide particles in a very finely divided state of about 50 A in diameter. Despite their size, these particles had some crystalline characteristics - they had semi-regular appearance; had limited solubility in ammonium oxalate (in darkness) and in sodium pyrophosphate; and sometimes gave ring-type electron diffraction patterns identifiable as goethite. The particles contained a high degree of substitution of aluminium for iron. They associated with other soil components, for example, forming surface deposits upon larger kaolin flakes or else microaggregates with smaller ones. They reacted with soil organic matter, which caused marked inhibition of arsenate uptake. Titanium oxides competed with iron oxides for arsenate, and were able to dominate uptake when iron oxides were removed chemically. The behaviour of other components towards arsenate was described, together with their appearance, composition and stability during a series of successive chemical treatments. No iron-organic complexes nor poorly crystalline aluminosilicates appeared to be present. Some reputedly selective reagents extracted excess aluminium, most of it coming from chloritized vermiculite. Small kaolin particles were also dissolved and, in some cases,. this caused fresh precipitation of iron oxides from iron previously held within the clay lattice.

Rubification of Terrae Rossae in Slovakia: A Mössbauer Effect Study

Abstract: Mineralogical and mFe Mrssbauer spectroscopic analyses were made on seven terrae rossae and two terraefuscae samples of Pliocene to Early Pleistocene age from Slovakia and limestone residues from their parent materials. In most of the samples, no mineral weathering or clay mineral formation could be detected by optical or X-ray powder diffraction investigation, compared with their parent limestone residues; only one terra rossa showed a strong weathering of primary feldspar and phyllosilicates and a high rate of clay formation, especially kaolinite. Mrssbauer measurements between 5 ~ and 300~ showed that hematite and goethite are the dominant color pigments in the rubified terrae rossae and their corre- sponding limestone residues. The mean particle size of hematite and goethite was estimated from Mrss- bauer effects and X-ray powder diffraction data to be 95 and 250 A, respectively. Reduced values of the hyperfine fields at 5~ of the soil iron oxides, as compared with those of the pure oxides, indicate a partial substitution of Fe(III) by A1. The hematite content correlates with the Munsell color notation of 5 of the 7 terrae rossae samples and their corresponding limestone residues. All terrae rossae samples showed higher hematite contents than their corresponding limestone residues, indicating that the rubification of such ma- terials is independent of the degree of weathering.

Pedological Significance of the Gravels in some Red and Grey Earths of Central North Queensland

Abstract: Red, yellow and grey earths consist largely of quartz, kaolin, and iron oxides and hydroxides, but little is known of the pedological processes that have resulted in their formation. Iron oxides and hydroxides, however, vary markedly according to their soil environments and can be used to study pedogenetic pathways in soil profiles. A detailed mineralogical examination has been made of two soils representing the red and grey end-members of the red-yellow-grey earth soil continuum in the semiarid tropical Torrens Creek area, 200-300 km southwest of Townsville, in central north Queensland. The profiles selected (a Plinthustalf and Haplargid of Soil Taxonomy) have high contents of ferruginous gravels in the solum, and are underlain by mottled, weathered sandstone. Four corresponding layers were sampled from each soil profile. Washed gravels from these samples were sieved into four size classes, and were sorted by hand into morphological groups, and into magnetic and nonmagnetic fractions. Subsamples of the resultant groups of gravels (>2 mm), of the fine earth ( < 2 mm), and of the whole soil, were analysed by X-ray diffraction. Quartz, kaolin, goethite and hematite were found in various proportions in the 205 analysed samples, but maghemite was restricted to the magnetic materials; few other minerals were detected. The mineralogical composition of each morphological group of gravels was found to be independent of the particle-size of the materials in the group. The iron oxide mineralogy of the soils suggests that the red, yellow and grey earths developed under different soil water regimes: free drainage and high organic matter oxidation rates in the red earths yielded hematite, with its strong red-pigmenting capacity, and goethite; profile saturation for relatively short periods of time has resulted in the formation of goethite, characteristic of the yellow earths and of the ferruginous gravels of the grey earths; and saturation of the grey earth profiles for lengthy periods has led to the loss of iron from the soil, which has then assumed the grey colour of the minerals (quartz and kaolin) comprising its matrix. These mineralogical interpretations are supported by field observations of contrasting hydrological regimes in the soils.

Characterization of iron in alkaline EDTA and NH4OH extracts of podzols

Abstract: Summary Mossbauer and ESR spectroscopy have shown that the iron extracted from the Bh horizons of an iron humus podzol and an iron podzol by EDTA at pH 9.1 is predominantly in the form of complexes* of polymeric Fe(III) hydroxide and oxide with organic matter (O.M.). Small amounts of monomeric Fe(III)-O.M. and Fe(III)-EDTA complexes also occur. In contrast EDTA at pH 7 extracts iron from these podzols predominantly in the form of iron-EDTA complexes. Some monomeric Fe(III)-O.M. complex also occurs in a pH 9.1 NH4 OH extract of these horizons and in a pH 9.1 EDTA extract of the B3 horizon of a peaty podzol. Dialysis experiments show that the particle dimensions of the polymeric hydroxy Fe(III)-O.M. complex, which accounts for about 66% of the Fe extracted from the iron humus podzol and about 36% of that from the iron podzol, are greater than 2.4 nm. The thermal behaviour of the Mossbauer peaks indicated that the size of the iron cores was of the order of 5 nm, thus suggesting that the complex probably consists of hydroxyiron cores surrounded by large organic molecules. Results from XRD and IR suggest that these hydroxyiron cores may have structural organizations similar to those of goethite and ferrihydrite. The relationship between these forms of iron in the extracts and those in the soil is briefly discussed.

Manufacture of spindle-shaped goethite having high axial ratio

Abstract: PURPOSE: To manufacture the titled goethite having a uniform particle size distribution and high dispersibility and suitable for use as a starting material for manufacturing magnetic metallic powder by carrying out the introduction of an oxidizing gas and the stirring of a slurry of a precipitated ferrous salt at once in a bubble tower. CONSTITUTION: An aqueous soln. of an alkali carbonate is mixed with an aqueous soln. of a ferrous salt such as ferrous sulfate to prepare a slurry of a precipitated ferrous salt, and by introducing an oxidizing gas such as air into the slurry at a reaction temp. above ordinary temp., the ferrous compound is oxidized to manufacture spindle-shaped goethite. In this method, a bubble tower is used so that the slurry can be stirred by blowing the gas. Thus, unbranched goethite having 0.05W0.50μm major axis size, ≥4 axial ratio, a uniform particle size distribution and high dispersibility can be manufactured. This goethite is especially suitable for use as a starting material for manufacturing magnetic metallic powder. COPYRIGHT: (C)1984,JPO&Japio

Goethite and hematite in some solls from the amazon region

Abstract: Goethite and hematite in four soi!s from the Brazilian Amazon region were examined. Color of the clay fractions in these soi!s became redder and darker with increasing iron content. Aluminium was isomorphously substituted for less than 33% of iron in both geothite and hematite. Two types of goethite at least were noticed in the morphology and the dehydration pattern. One type showed hexagonal or square plates in the electron micrograph, and lost most of the structural water at a temperature near 370°C. Another was acicular in morphology, and most of the structural water was released near 300°C. The particles of hematite in the electron micrograph were very fine, about 5 to 8 nm in diameter, which was approximately one-tenth smaller than that reported in the other studies. Tbe phenomenon for soi! hematite to act as the cementing materials on the formation of stable microaggregates was also observed by the electron microscopy.

Iron oxide minerals in soils of the Ha'apai group, Kingdom of Tonga

Abstract: The iron oxide mineralogy of three soils from the Ha'apai Group (c. latitude 19°50?S., longitude 174°30' W.), Kingdom of Tonga, has been investigated. The Group consists mainly of an archipelago of low coral atolls. Soils are formed in the andesitic tephra which overlie the coral. Accessions of marine salts are high and give rise to high soil pH values (>7) and high concentrations of exchangeable cations. The soils are dark reddish brown to reddish brown in colour, with limited colour differentiation with soil depth, and they are not hqdromorphic. The results of study of whole soils and size fractions by chemical extraction, X-ray diffraction, differential thermal analysis, Moessbauer spectroscopy, and by measurement of variation of magnetic attraction following heating to various temperatures, lead to the following conclusions: iron oxide minerals comprise 7-12% by weight of the soils; the predominant clay size iron oxide is very poorly crystalline aluminium-substituted lepidocrocite (a-Fe 0.8Al 0.2,OOH); ferrihydrite is probably also present in the clay fraction; lepidocrocite and ferrihydrite together account for 50-60% of the total iron in the soils studied; magnetite, probably partially oxidized towards maghemite, is present, particularly in sand and silt fractions, and accounts for about 10% of the total iron in the soils. The remainder of the total iron occurs in unweathered minerals in the silt and sand fractions and in the structure of halloysite in the clay fraction. The common soil iron oxides, goethite and hematite, have not been detected. Although the occurrence of lepidocrocite is usually linked with hydromorphic soil conditions, this report, along with others, suggest that it is also found under non-hydromorphic conditions.

A partial equilibrium model to characterize the precipitation of ferric ion during the leaching of chalcopyrite with ferric sulfate

Abstract: A partial equilibrium model has been developed and used to characterize the conditions under which precipitation of ferric ion occurs during the dump leaching of chalcopyrite ores. The precipitates which have been considered include amorphous Fe(OH)3, α-FeOOH (goethite), and Na+, K+, Ag+, Pb2+, and H3O+ jarosites. Solution of the model equations makes possible the determination of the concentrations of the solution species during leaching of the mineral. The concentration product for Fe(OH)3 (am) and α-FeOOH was calculated for changing solution concentrations and compared with the solubility product constants to determine when precipitation would be expected thermodynamically. The K+, Na+, Ag+, and Pb2+ concentrations that would be necessary to satisfy the solubility product constants for the corresponding jarosites were calculated for various initial concentrations and varying amounts of O2 consumption.

Multifactor Kinetics of Phosphate Reactions with Minerals in Acid Soils: II. Experimental Curve Fitting1

Abstract: A kinetic model of phosphate reactions with minerals in acidic soils was used to simulate experimental results obtained under a variety of conditions based on three factors—solution pH, solution concentration, and mineral specific surface area. Three minerals with different reactivity (kaolinite, gibbsite, goethite) were studied to check the adaptability of the model and show the effect of mineral properties on reaction with phosphate. The experimental data as well as the kinetic models showed that high pH values, low concentrations of the phosphorus in the reacting solution, and small specific surface area will reduce retention of phosphate. Any other change of the three factors increases the retention capability. The model shows its flexibility in simulating phosphate reactions with different minerals. The results show promise for the miltifactor approximation of phosphate reactions with soil minerals in acid to neutral soils.

Grinding-induced effects on goethite (α-FeOOH)

Abstract: The mechanochemical decomposition of goethite (α-FeOOH) into hematite (α-Fe2O3) has been studied by X-ray powder diffraction, transmission electron microscopy, and N2 adsorption at 77°K. It is postulated that the energy brought about by the goethite deformation during grinding may act as driving force for the transformation. No microporosity was observed during the transformation and only mesoporosity can be detected. The changes in specific surface area are related to changes in particle size and to the reduction in volume during the goethite to hematite transformation.

A Mössbauer Study of Some Australian Iron Ore Minerals

Abstract: Six specimens of Australian iron ore, three hematite-rich and three goethite-rich, have been investigated by M6ssbauer spectroscopy at both 300 K and 4.2 K. The resulting spectra provide data relevant to crystallite particle size variations in the hematite and goethite, the extent of isomorphous replacement, and the existence within one specimen of a poorly defined goethite-like material. THE mineralogy of iron ore is of considerable interest, both because of the widespread occurrence of such ores and because of their economic importance. The Australian continent contains very large deposits of high-grade iron ore and Australia is well known as the world's largest iron ore exporter. The ore is essentially hematite derived from the desilicification and iron-enrichment of banded iron formations of Proterozoic age. The major ore bodies are situated in the north west of Western Australia. This area also contains large deposits of pisolitic limonite of Tertiary age which have great potential as future commercial sources of iron ore. The mineralogy of these ores has been described in a number of papers including Harms and Morgan (1964), Macleod (1966), Trendall and Blockley (1970), Ayres (1971, 1972), and Klein and Gole (1981). Although the techniques used by these investigators include optical microscopy, electron probe microanalysis, and X-ray diffraction, there are indications that not all of the mineralogical features of the ores have been determined (Ostwatd, 198 l a). Precise definition of iron ore mineralogy is not simply academic, as iron ore mineralogy (and microtexture) influences the blast furnace reduction of lump ore and the characteristics of iron ore * Now at The Broken Hill Proprietary Company Limited, Central Research Laboratories, Shortland, NSW, Australia, 2307. (~) Copyright the Mineralogical Society sinter (Ostwald, 1981b; Burghardt and Grover, 1981). For this reason we have attempted to obtain additional information on the major minerals comprising Australian iron ores by the use of M6ssbauer spectroscopy (e.g. Bancroft, 1973). This technique is particularly suitable for the study of the iron species present in soils and clays, as it is usually able to provide quantitative analyses for finely divided materials which are not amenable to X-ray diffraction investigation. One particularly useful feature of such measurements is the ability to determine the degree of isomorphous lattice replacement of the iron minerals, and Fysh and Clark (1982a, b) have recently published the data required in order to make such determinations for aluminous goethites and hematites. Hemati te and goethite are by far the most commonly occurring iron-containing minerals in Australian iron ores, and so we have carried out M6ssbauer analysis on a variety of specimens which represent the major microtypes of these minerals as they occur in such ores. Specimens examined. Six specimens, three composed essentially of hematite and three essentially of goethite were selected for this study. They were chosen from a range of iron ores because they represented differing modes of genesis of the minerals. Brief descriptions of the ores from which the specimens originated, and their locations, are given below. (1) Marra Mamba ore (23 ~ 30' S., 120 ~ E.), Western Australia. This ore results from the desilicification and iron enrichment of Proterozoic banded iron formations containing abundant diagenetic iron silicates such as stilpnomelane and minnesotaite (Neale, 1975). The resulting iron ore contains abundant micro-fibrous goethite (fig. la) as well as smaller amounts of other oxides. (2) Deepdale ore (22 ~ S., 116 ~ E.), Western Australia, was formed by colloidal deposition of iron oxides in the 210 S . A . F Y S H A N D J. O S T W A L D FIG. 1. Photomicrographs of polished sections of the specimens examined. The scale bar represents 20 #m in each case. (a) Marra Mamba. (b) Deepdale. (c) Whyalla. (d) Whaleback. (e) Whaleback scree. ( f ) Koolan. A U S T R A L I A N I R O N ORE M I N E R A L S form of pisoliths along river valleys during the Mesozoic. Erosion of the strata of essentially geothite pisoliths (fig. lb) during the Tertiary resulted in mesaform deposits. (Harms and Morgan, 1964.) (3) Metacolloidal goethite from the Middleback Ranges iron ore [Whyalla ore] (33 ~ S., 137 ~ E.), South Australia. A specimen of goethite occurring as a fracture-filling veinlet in the hematite ores of the above area was chosen as a third example of goethite. Microscopy shows the presence of colloform structures (fig. lc) and suggests a metacolloidal origin. (4) Polycrystalline hematite ore (fig. ld), Mt. Whaleback deposit (23 ~ 30' S., 120 ~ E.), Western Australia. This ore is the result of desilicification and iron enrichment of Proterozoic banded iron formations, accompanied by subsequent recrystallization. (5) Hematite scree ore, Mt. Whaleback deposit. This ore is comprised essentially of particles of the above polycrystalline hematite cemented by finely porous hematite (fig. le). (6) Dense polycrystalline hematite ore, Koolan Island (16 ~ 08' S., 123 ~ 15' E.), Western Australia. This ore consists of mosaics of dense hematite grains (fig. if) and is apparently the result of iron enrichment of metamorphosed clastic sediments. M6ssbauer analysis. Spectra of the ores have been taken at both 300 K and 4.2 K, using the same methods as have been described previously (Fysh and Clark, 1982a). The shape of the M6ssbauer spectra observed for Fe in hematite and goethite has been discussed extensively (Fysh and Clark, 1982a, b). In these earlier studies the M6ssbauer spectra of synthetic hematites and goethites could be fitted by broadened Lorentzian lines, the broadening being the result of the presence of a range of Fe nuclear environments in the Al-substituted structures. In naturally occurring minerals, the range of Fe environments may be so large that the observed line shape is no longer well approximated by a Lorentzian. Fysh (1982) has shown that such spectra may be fitted by the pseudo-Lorentzian line shape 1 (1) y(x) 2 ~< ~ -%< 3.45 (2x'~ 1+C ) which is due to Price (1981). This line shape has been used to fit the spectra taken here. Results and discussion Goethitic ores. The room-temperature spectra of the Marra Mamba, Deepdale, and Whyalla specimens are shown in fig. 2. That of the Marra Mamba ore consists of the superposition of a sharp, welldefined magnetically split spectrum on a relaxed magnetically split subspectrum. The relaxed subspectrum has a much smaller splitting. There is also a doublet between the inner peaks of the relaxed spectrum, and the origin of this will be considered shortly. On the basis of their approximate splittings, the large and small field subspectra 211 may be identified as being due to hematite and goethite respectively. The spectrum of the Deepdale sample (fig. 2c) is qualitatively similar to that of the Marra Mamba ore, but the spectral lines of the outer (hematite) hyperfine split field are asymmetrically broadened. The relative goethite content is apparently greater for the Deepdale ore, and for the Whyalla specimen it appears that only goethite is present. The asymmetrically broadened (relaxed) appearance of all of the goethite subspectra, as well as that of the Deepdale hematite subspectrum, is due to superparamagnetic (SPM) relaxation of the mineral microcrystals (e.g. Bean and Livingston, 1959; Dunlop, 1981; Fysh and Clark, 1982a). The magnetic moments of small single domain crystallites fluctuate rapidly, resulting in a reduced (or even zero) time-averaged magnetic field at the Fe nucleus. The asymmetry of the spectral lines is the result of the presence of a range of mineral domain sizes. Some authors (e.g. Murad, 1979) have interpreted such spectra (obtained for goethites) as being a consequence of the isomorphous replacement of Fe in the crystal structure. However, both decreasing particle size (i.e. SPM) and lattice dilution have been shown (Fysh and Clark, 1982a, b) to have the same effect on room-temperature iron oxide spectra, so that the relative contribution of each can only be assessed by taking spectra at low ( ~ 77 K) temperatures. Fluctuations in the magnetization direction of SPM particles are thermally activated, so that at low temperatures any reduction in hyperfine splitting from that of the pure mineral may usually be assumed to be due to isomorphous lattice replacement. In addition, the spectra are considerably easier to fit in the absence of relaxation effects. Before considering the 4.2 K spectra of the goethitic specimens, however, it is worth noting that some information may be gained from the relaxed 300 K spectra. Thus, for example, the more relaxed shape of the hematite subspectra in the Deepdale ore spectrum cf. that for the Marra Mamba ore is a reasonable indication that the particle size of the hematite in the latter is somewhat greater. The 'particle size' referred to, however, relates to the size of coherent magnetic domains in the hematite. This may not always be coincident with that determined by microscopy and other techniques, due to the possible presence of dislocations, fine cracks, etc. which disrupt the magnetic continuity of 'large' grains. The relationship between true particle size and that determined by MSssbauer and X-ray diffraction methods has been further discussed by Amelse

Fine magnetic metallic powder having small specific surface area and its manufacture

Abstract: PURPOSE: To manufacture magnetic metallic powder having a small specific surface area by reducing spindle-shaped goethite having a specified major axis size, a specified minor axis size and a specified axial ratio with a reducing gas. CONSTITUTION: Spindle-shaped goethite having 0.05W0.3μm major axis size, 0.015W0.04μm minor axis size and 3W15 axial ratio is optionally dehydrated by heat treatment to prepare iron oxide, and the goethite or the iron oxide is reduced with a reducing gas at about 300W500°C. The starting material is coated with a sintering inhibitor such as potassium silicate before the reduction. The amount of the inhibitor is about 5W10wt% of the amount of the goethite. Magnetic metallic powder having 0.05W0.2μm major axis size, 4W10 axial ratio and 30W55m 2 /g specific surface area is obtd. The specific surface area is measured by adsorbing gaseous N 2 by the BET method. COPYRIGHT: (C)1985,JPO&Japio

Intemperização de rochas ultrabásicas no rio grande do sul, brasil

Abstract: Results of a study on ultrabasic rock weathering under subtropical climate are presented. The mineralogical evolution leads to the formation of nontronite and amorphous materials from the wrathering of mafic-silicates, while the plagioclase, in the same rock, yields kaolinite and montmorilonite. The transformation of amorphous materials into goethite occurs in the soil and the clay minerals are preserved as aluminous nontronite. The weathering action leads to strong loss of Mg and Ca, with partial retention of Si. Mg loss is more intense than that of Ca when both are components of silicates. If Ca is a carbonate component, as occurs in the serpentinites, its mobilization is quicker than that of Mg. Fe can be partially mobilized when it is contained in mafic silicates, but when it is a component of magnetite, as in serpentinites, Fe becomes absolutely fixed. Al and Ti are flxed. Mn, Cr, Ni, Co, V and Cu have the same behavior as Fe. Na behaves as Ca. During the first stages of weathering, K is lost, but it is fixed again in the soil by organic compounds and clay minerals. The groundwater and supergenic mineral compositions are in equilibrium, and both indicate a sialferrtzation weathering type. The relative mobilities, based on the groundwater composition, show some differences as compared to the mobilities based on the use of the solid phase composition. Such differences are caused by some imprecisions in the methods themselves.

Chemical and charge characteristics of kaolinitic soils of south-east Queensland

Abstract: Cation exchange capacity at field pH and net negative charge at pH 8.5 of 39 kaolinitic soils were studied in relation to surface area and other soil characteristics. All soils exhibited an anion exchange capacity at field pH, but this was very low compared with cation exchange capacity. Little evidence could be found for the presence of amorphous aluminium or silica, or short-range order alumino-silicates on the basis of acid oxalate-extraction, in contrast to Tiron extraction. All samples had significant permanent negative charge as deduced using the method of Gillman and Uehara, in addition to pHdependent charge. The former was strongly related to the exchangeable divalent cations, and this may explain the great variation in base saturation observed. Most of the charge in these soils is derived from the small poorly crystalline kaolins, although at high pH oxalate-extractable iron contributes significantly to the negative charge. Based on the results for those soils containing less than 5% iron oxide, surface area determined by ethylene glycol is linearly related to the net negative charge at pH 8.5. The average surface charge density on the soils containing <5% hematite and goethite measured at this pH value is 0.9 nm2/charge. Hematite and goethite show much lower negative charge densities and effectively dilute the active surface.