Showing papers on "Goethite published in 1980"

The adsorption of lead and other heavy metals on oxides of manganese and iron

Abstract: Measurements were made of the adsorption of cobalt, copper, manganese, nickel, lead, and zinc on nine synthetic manganese oxides and three synthetic iron oxides, to determine the mechanism by which lead accumulates in the manganese oxides in soils. Adsorption of lead by the manganese oxides was up to 40 times greater than that by the iron oxides, and lead was adsorbed more strongly than any of the other ions studied by all of the oxides except goethite. This is considered to be the reason for the accumulation of lead in the manganese oxides in soils. No evidence was found for the oxidation of lead, nor for the formation of specific lead-manganese minerals.

A textural and mineralogical study of the relationship of iron ore to banded iron-formation in the Hamersley iron province of Western Australia

Abstract: Microscope studies of a wide range of ores and fresh, oxidized, or partly iron-enriched, banded iron-formation (BIF) have shown a consistent sequence of alteration of the primary constituents, chert, magnetite with or without hematite, carbonates, and silicates, leading to the formation of martite-(hematite)-goethite ores which form the bulk of the reserves of the Hamersley Iron Province. Primary hematite survives with little change; magnetite oxidizes to hematite (martite) or in part to lacunar phases between magnetite and maghemite (kenomagnetite), which in turn commonly is altered by hydration to goethite. Subsequent leaching of this goethite in preference to martite leads to a variety of skeletal textures which may help identify the original magnetite, despite destruction of martite lamellae by recrystallization. Chert, carbonates, and silicates are either replaced by goethite or leached from the system, resulting in thinning of the orebodies with respect to their parent banded iron-formations. Preservation of macroscopic features, such as mesobanding, and microscopic features, such as pseudomorphs, is compelling evidence of supergene enrichment which, together with residual upgrading by leaching of these iron-formations, produces ores which typically assay 62 percent Fe, ignition loss of 4 to 6 percent, and >0.07 percent P. With increasing maturity, part of the goethite has converted to fine-grained hematite in some of these martite-(hematite)-goethite ores. Though overall the secondary hematite is quantitatively unimportant, some deposits may be significantly upgraded by this process, and it is this variability that is implied by the use of brackets in the classification.A second ore type, characteristic of the Tom Price and Whaleback mines, consists essentially of residual primary components, martite and hematite, with abundant secondary hematite, most of it platy but some anhedral. These martite-hematite ores appear to have formed by a low-temperature process in which some of the goethite or its precursor, in ores of the martite-(hematite)-goethite type, has converted to platy hematite in contrast to the fine-grained and often cryptocrystalline material of the normal ores. This partial transformation has resulted in increased permeability of the deposits which in turn has allowed leaching of the remnant goethite. The Paraburdoo 4E mine represents an arrested stage of development in which a large proportion of this unconverted goethite is still present, whereas the Tom Price and Whaleback deposits represent the most mature ores in the province. In these, leaching has removed the bulk of the goethite, leading to typical assay values of >64 percent Fe, 1 percent loss on ignition, and <0.05 percent P.The supergene ores of the province can be classified in terms of a maturity scale based on the type and amount of secondary hematite replacing goethite. Thus martite-goethite ores without significant secondary hematite are considered to be the least mature. Examples of these have been found in a limited survey of the Marra Mamba Iron Formation ores. The Brockman Iron Formation deposits at Koodaideri, the Brockman syncline, and Metawandy provide examples of more mature ores with increased secondary hematite and are classified as martite-(hematite)-goethite ores. Ancient deposits (early to middle Proterozoic) with abundant secondary platy hematite but with significant residual goethite are classified as the Paraburdoo type. Substantial leaching of this goethite leads to the most mature ores of the province, the martite-hematite deposits of the Tom Price-Whaleback type.

Formation and properties of Fe(II)Fe(III) hydroxy-carbonate and its possible significance in soil formation

Abstract: Small amounts of Fe(IlI) induce precipitation of Fe(II) from carbonate solutions around neutral pH values. The reaction involves the formation of Fe(II)Fe(IlI) hydroxy- carbonate, a green, layer-structured compound of the pyroaurite group of minerals. Variations in the concentration of Fe(II) in the solution phase, and in the form and amounts of the total Fe(III) in the system, may cause other phases such as magnetite and siderite to form also. Freeze-dried Fe(II)Fe(III) hydroxy-carbonate topotactic alteration to a magnetic phase, !~resum - ably maghemite, when stored under vacuum. The compound is readily oxidized in air in either the moist or dry state, rapidly becoming yellow or yeUow-brown in colour. Oxidation leads to the formation of either goethite, lepidocrocite, ferrihydrite or mixtures of these phases, depending on the mode of oxidation and the impurities present. The similarity between the rapid colour changes and the oxidation products of the blue-green precipitates in gleyed soil horizons and this Fe(II)Fe(III) hydroxy-carbonate leads to the speculation that this and related compounds may be the meta-stable precipitates in such soils, rather than a previously postulated hydro-magnetite phase. Eh and pH conditions for the formation of Fe(II)Fe(III) hydroxy-carbonate are given, and are in the range encountered in the soil environment. It is necessary to utilize systems that approximate to those found in pedogenic environ- ments if an understanding of the formation and mutual association of soil iron oxides is to be gained from synthesis experiments. Additionally, it is important to be aware of possible intermediate, meta-stable phases that may form in soils, since the transformation pro- ducts of these phases may also depend on environmental conditions. These intermediate phases would not be observed during the normally more direct syntheses involving high or low pH values and elevated temperatures. Taylor & Schwertmann (1974) showed that the common soil iron oxides could all form from an Fe(II) chloride solution at ambient temperatures and near neutral pH values, the products depending on the rate of oxidation and the Fe(II) concentration in solution. In a further simulation of soil conditions these two authors (Taylor & Schwertmann, 1978) used Fe(II) carbonate dissolved in CO2-charged water. They were able to ~ynthesize lepidocrocite, goethite or ferrihydrite (a precursor of hematite and goethite) depending on concentration and rate of oxidation of the Fe(II) in solution, and demonstrated the effects of soluble AI hydroxy species on the formation of these phases. However, maghemite, a further common pedogenic iron oxide, was not formed from the carbonate system. As an extension to this work, Taylor & McKenzie (1980) produced an Fe(II)AI(III) hydroxy-carbonat e under conditions that could be encountered in certain soils. This compound was iso-structural with hydrotalcite, a mineral of the pyroaurite group, but was very unstable and transformed, under aqueous oxidation, to Al-substituted goethite.

Natural Occurrence of Feroxyhite (δ'-FeOOH)

Abstract: Feroxyhite (δ′-FeOOH) in association with goethite and lepidocrocite was found as a dominant mineral in some rusty precipitates from Finland. These precipitates formed in the interstices of sand grains from rapidly flowing, Fe(II)-containing water which was very quickly oxidized as it flowed through the sediment. The mineral is distinguished from other FeOOH forms and from ferrihydrite mainly by its X-ray powder diffractogram. Further characteristics are an acicular morphology (possibly thin, rolled plates), an internal magnetic field at 4°K of ∼510 kOe, Fe-OH stretching bands at ∼2900 cm−1 and Fe-OH bending bands at 1110, 920, 790, and 670 cm−1, and an oxalate solubility between ferrihydrite and goethite or lepidocrocite. Feroxyhites with very similar properties were synthesized by oxidation of an Fe(II) solution with H2O2 at a pH between 5 and 8.

The influence of aluminum on iron oxides. VI. The formation of Fe(II)-Al(III) hydroxy-chlorides, -sulfates, and -carbonates as new members of the pyroaurite group and their significance in soils.

Abstract: In the absence of oxygen, Fe(II) chloride, sulfate, and carbonate solutions react at pH 6.5 to 7 with aluminum hydroxide suspensions to form new Fe(II)-Al(III) hydroxy anion compounds of the pyroaurite group. The Fe(II)-Al(III) hydroxy-chloride and -sulfate compounds are isostructural with Fe(II)- Fe(III) “green rust” compounds with A1 essentially substituting for Fe(III). Where CO,2 is the only anion in the system, an Fe(II)-Al(III) compound isostructural with hydrotalcite is formed. Either in the dried or wet state, these compounds are unstable in air due to oxidation of Fe(II). Oxidation of the dried sample in air yields akaganeite or aluminous ferrihydrite, whereas, if the sample is maintained in a moist condition and oxidized by air under water, lepidocrocite or aluminous goethite is produced along with small amounts of ferrihydrite. On X-ray powder diffraction, the lepidocrocite so formed commonly shows no diagnostic (020) basal reflection, or one with a markedly reduced intensity. The products of oxidation, and the rapidity of their formation, appear to be dependent on the composition of the initial double hydroxy compound and the conditions under which the oxidation is carried out.

The effect of [OH] on the goethite produced from ferrihydrite under alkaline conditions

Abstract: In alkaline solution ferrihydrite adsorbs OH, the amount initially adsorbed being dependent on [OH]. At high pH values ferrihydrite transforms rapidly to goethite with the rate of transformation also depending on [OH]. With time, goethite crystals grow, the total surface area of the solid decreases and OH previously adsorbed is progressively desorbed and reappears in the supernatant liquid. At any stage during the transformation the amount of OH adsorbed onto the solid is linearly related to both the amount of residual ferrihydrite and to the specific surface area of the solid. Regression equations indicate that the OH-adsorption capacity per unit surface area is similar for the initial ferrihydrite and the goethite produced (6 to 7 μmole OH m −2 ). X-Ray diffraction suggests that the goethite crystallites formed at high [OH] are smaller in both the crystallographic a and b dimensions. At 25°C the goethite crystals develop their final small thickness along the crystallographic a axis after a very short time. Subsequently they grow almost exclusively in width (along b axis) and length ( c axis) until the ferrihydrite is completely transformed.

Association of trace elements with iron oxides during rock weathering

Abstract: The association of trace elements with Fe oxides during the early stages of rock weathering was determined by analysis of fresh diabase and granite rocks, their associated whole and size-separated saprolites, and goethite by neutron activation and X-ray fluorescence The same elements are found to be associated with Fe oxides when the results are interpreted by analysis of correlation, by the distribution of elements in the various size fractions by the effects of removing free Fe oxides, and by direct analysis of geothite from the saprolite The elements Co, Cr, Mn, Sc, Th, U, Zn, and the heavy rare-earth elements during the weathering of diabase, and As, Co, Cr, Sc, Th, U, Zn, and the heavy rare-earth elements during the weathering of granite are associated with Fe oxides The concentrations of Mn are too low in this system to separate the effects of Mn oxides from those of Fe oxides

Infrared study of the adsorption of carboxylic acids on haematite and goethite immersed in carbon tetrachloride

Abstract: A novel infrared cell is described for the study of adsorption behaviour in situ at the solid/liquid interface. Spectra are reported of goethite immersed in solutions of succinic acid in carbon tetrachloride and of goethite and haematite in solutions of acetic, dodecanoic, dodecyl succinic and dodecenyl succinic acids. Chemisorptive interactions predominated and led to adsorbed carboxylate species primarily in the chelating bidentate configuration. The products of adsorption of substituted succinic acids also gave infrared bands characteristic of undissociated carboxylic acid groups. The ratio of COOH groups to carboxylate anions was greater for haematite than for goethite and greater for dodecenyl succinic acid than for dodecyl succinic acid. Alkyl chains close to the goethite or haematite surfaces hindered a mode of adsorption in which both carboxylic acid groups in an adsorbate molecule simultaneously interacted with a pair of adjacent chemisorption sites. The hindering effect was promoted when the hydrocarbon chain contained an alkenyl segment.

Manufacture of acicular, ferrimagnetic iron oxide

Abstract: A process for the manufacture of acicular ferrimagnetic iron oxide by dehydrating acicular iron(III) oxide hydroxides to give acicular iron(III) oxides, then reducing these iron(III) oxides at from 300° to 650° C. by means of an organic compound which decomposes in this temperature range, and oxidizing the reduced product with an oxygen-containing gas at from 200° to 500° C., wherein the acicular iron(III) oxide hydroxides employed consist of a mixture of goethite and lepidocrocite, containing at least 60% of the latter, and the dehydration is carried out at from 250° to 700° C.

Influence of adsorbed anions on the dehydroxylation of synthetic goethite

Abstract: The influence of surface structure on the dehydroxylation of synthetic goethite has been studied using heat-flux differential scanning calorimetry. Adsorption of various anions by goethite causes a progressive change in both the amount and environment of surface hydroxyls and this is reflected by changes in the DSC curves. These alterations indicate the importance of surface features in determining the course of dehydroxylation and further suggest that, in studies of this type of reaction, the use of synthetic products known to be free of surface contaminants could prove to be of great value in understanding dehydroxylation mechanisms.

The influence of aluminum on iron oxides; VII, Substitution of Al for Fe in synthetic lepidocrocite

Abstract: The presence of Al hydroxy species in solution during the synthesis of lepidocrocite had been previously found to influence the reaction towards goethite formation. However, under certain conditions, which are not unrealistic in terms of the natural soil environment, this influence does not occur, and Al appears to substitute for Fe(III) in the lepidocrocite structure. This substitution causes the unit-cell dimensions to decrease along the “a” direction and to increase along the “b.” From the differential line broadening of X-ray powder diffraction peaks, the incorporation of Al was found to inhibit crystal growth preferentially in the b-axis direction, the hkl peaks being more broadened the higher the value of k relative to h and l. Al-substituted lepidocrocites have been suggested to occur in soils, and although they can be synthesized under conditions approaching those expected in soils, it is considered that their formation in nature is unlikely or restricted to unusual environments.

Effect of adsorption of phenoxyacetic acid herbicides on the surface charge of goethite

Abstract: Summary Surface charge titration measurements, performed on goethite in the presence of absorbed herbicide ions, indicate that the result of adsorption is to cause an increase in the positive charge of the mineral surface. The titration results, used in conjunction with adsorption measurements to calculate the exchange coefficients for the adsorption reactions, show that there is a significant selectivity in adsorption of the herbicides over the indifferent counterion nitrate. This is believed to be due to the existence of favourable van der Waals interactions between the adsorbed herbicide ions.

Mossbauer study of the attenuation of iron in an irrigated greensand lysimeter

Abstract: Fe57 Mossbauer spectroscopy has been used to determine the nature of iron-containing minerals in Lower Greensand samples from an experimental lysimeter at Uffington, Oxfordshire, both before and after a three-year irrigation with a synthetic heavy metal leachate. Analysis of the spectra measured at 300°, 77°, and 4.2°K and at 4.2°K in an applied field of 45 kOe shows that iron is present in the uncontaminated sandstone in fine-grained goethite (α-FeOOH) and glauconite. In the irrigated samples iron is precipitated as a fine-grained ferric hydroxide gel having values for the hyperfine field at 4.2°K of 435 and 470 kOe. The stability of the gel over the three-year period of irrigation may be explained by surface energy considerations.

Thermal transformation of goethite into haematite in alkali halide discs

Abstract: Parallel thermal treatments have been investigated with powder mixtures containing 33 wt % goethite in alkali halides (KCl, KBr, KI and CsI) and with pressed discs having the same compositions. Infrared and X-ray studies have shown that the reaction scheme occurring in the discs includes: (1) dehydroxylation of goethite leading to the formation of protohaematite (at 250°C) and (2) recrystallization of protohaematite into haematite (at 430°C). On the other hand, only the dehydroxylation stage occurs in the powder mixtures and protohaematite persists even after prolonged heating at 430°C. The recrystallization stage, which is accompanied by crystal growth, is very slow in the CsI discs, whereas crystal growth by aggregation (sintering) is essential in the CsI disc but not in the KCl, KBr and KI discs. The results of weight loss during the thermal treatment indicate that in addition to dehydroxylation other reactions are taking place, mainly in the discs. These reactions may include ion exchange and reduction of ferric iron. Water adsorption of the various salt-free products was studied in three different environments, namely from liquid water and from 100 and 40 % relative humidities. These three experimental series show that the protohaematites obtained in potassium halide powder mixtures are hydrophilic, whereas those obtained in discs are hydrophobic. These differences in the surface properties may indicate that crystal perfection during the recrystallization stage begins in the Fe2O3/K-salt interface.