Showing papers on "Goethite published in 1982"

The 5-M-NaOH concentration treatment for iron oxides in soils

Abstract: The boiling 5-M-NaOH treatment was found to aid in the identification and characterization of goethite and hematite by effectively concentrating the two Fe oxides in kaolinitic-gibbsitic soil clays. No transformations of goethite to hematite or hematite to goethite were detected, but poorly crystalline, highly Al-substituted goethite was found to dissolve and recrystallize into a more well-crystalline, less Al-substituted goethite in samples low in Si. The Si released from kaolinite was sufficient to block goethite dissolution and recrystallization in kaolinitic samples, but noncrystalline silica had to be added to samples rich in gibbsite to minimize this effect.

The Point of Zero Charge of Natural and Synthetic Ferrihydrites and Its Relation to Adsorbed Silicate

Abstract: The point of zero charge (pzc) of synthetic Fe-oxides is well documented and usually ranges between pH 7 and 9 (Parks, 1965; Schwertmann & Taylor, 1977). In contrast, the pzc of natural Fe-oxides has only rarely been determined. Using electrophoretic mobility, Van Schuylenborgh & Arens (1950) found that a natural goethite had a much lower pzc (∼3) than synthetic goethites. They attributed this to better crystallinity of the natural goethite caused by slower crystallization. Soils dominated by Fe- (or Al-) oxides rarely have pzc values as high as those of pure oxides. This is usually attributed to the presence of negatively charged impurities such as clay silicates and organic matter (Parfitt, 1981). Ferrihydrite, a natural, poorly-crystalline Fe-oxide mineral of bulk composition 5Fe2O3.9H2O, occurs in hydromorphic soils (Schwertmann et al., 1982) and is the main component in ochrous precipitates formed when Fe-bearing fresh waters come in contact with air (Schwertmann & Fischer, 1973; Carlson & Schwertmann, 1981). Under these conditions the ferrihydrite is reasonably free of other charge-active minerals. The aim of this study was to find out if the pzc of these natural ferrihydrites differed from those of synthetic samples.

Aluminous goethite: A mössbauer study

Abstract: Mossbauer measurements at 300 K, 77 K and 4.2 K and X-ray data are presented for synthetic aluminous goethites (α Fe1−x Al x OOH) in two series containing up to 15 mole percent aluminium (hydrothermal preparation) and 19 mole percent aluminium (low-temperature preparation). The Mossbauer spectra for specimens at 300 K and 77 K display broadened and relaxed line-shapes with the relaxation rate increasing with aluminium substitution, whereas all the 4.2 K spectra can be described by a single magnetically split spectrum. At 4.2 K the magnitude of this splitting is 505 kOe for pure goethite and it decreases by 0.52 kOe per mole percent aluminium substitution. The absolute value of the recoil-free fraction f at 4.2 K has been measured for pure goethite and for aluminous goethites containing 7, 15 and 19 mole percent aluminium; it increases from f=0.69±0.02 to f=0.89±0.02 in this range. The increase is attributed to a stiffening of the goethite lattice as it contracts to accommodate the smaller aluminium ion. At 300 K f is found to decrease from f=0.65±0.05 for pure goethite to f=0.50±0.03 for goethite with 19 mole percent aluminium.

The formation of goethite, jarosite, and alunite during the weathering of sulfide-bearing felsic rocks

Abstract: Quantities of goethite and jarosite produced by weathering correlate with abundance and composition of sulfide minerals originally in rocks. To characterize processes forming these minerals, chemical weathering of sulfide-bearing rocks was simulated using differential equations which describe mass transfer between aqueous solutions and minerals (Helgeson, 1968).Goethite begins precipitating during reaction between meteoric water (f (sub O 2 ) = 10 (super -06) atm) and sulfides after dissolution of 6.7 X 10 (super -9) g pyrite or 6.0 X 10 (super -9) g chalcopyrite per 1,000 g H 2 O. Reaction of the oxygen dissolved in 1,000 g water that is initially saturated with the atmospheric abundance of oxygen consumes 0.0085 g pyrite or 0.013 g chalcopyrite. Goethite is the only reaction product. The calculations predict that weathering produces jarosite or alunite after goethite when >0.04 moles of oxygen have been consumed per 1,000 g H 2 O and where rates of oxygen replenishment approximately equal or exceed consumption. Simultaneous reactions between K-feldspar, an aqueous solution, and pyrite or chalcopyrite produce alunite and goethite if the irreversible molar flux of Fe/Al is less than 0.5. Reactions with fluxes of Fe/Al between 0.5 and 1.0 produce alunite, goethite, and jarosite; those with Fe/Al fluxes greater than 1.0 generate only jarosite after goethite.Following saturation of the solution with jarosite, the mass ratio, goethite/(goethite + jarosite) decreases smoothly from 1.0 to 0.0 accompanying continuous dissolution of pyrite and chalcopyrite. The interval of reaction progress over which goethite and jarosite coexist increases, relative to pyrite and K-feldspar reactions, when weathering involves muscovite or chalcopyrite. In simulations whose sulfides have been totally oxidized, this ratio varies antithetically with the volume percent sulfide and/or ratio of pyrite/(pyrite + chalcopyrite) initially present, a prediction consistent with geologic observations.

Influence of relative humidity on the crystallization of Fe(III) oxides from ferrihydrite

Abstract: Ferrihydrite prepared in different manners was kept under relative humidities ranging from 75 to 100% and at temperatures of 45° and 55°C for 180 days. Ferrihydrite transformed to hematite and goethite at relative humidities close to 100%, but at lower relative humidities the transformation was less pronounced and hematite was highly favored over goethite. Increasing temperature also favored hematite over goethite, and Al substitution completely prevented goethite formation. These results suggest that hematite can form in relatively dry, warm soils or sediments, although more slowly than in moister environments.

Quantitative determination of goethite and hematite in kaolinitic soils by X-ray diffraction

Abstract: In the past, two factors have impeded the quantitative estimate of Fe-oxides in soils by X-ray diffraction. First, Fe-oxides are still quite often considered X-ray amorphous, although numerous results, e.g. a low ratio of oxalate- to dithionite-soluble Fe, have indicated the opposite. Second, even if crystalline, the cocentration of Fe-oxides in many soils is low, thereby complicating their identification by XRD. Recently, however, more sensitive methods such as Mossbauer spectroscopy and Differential-XRD (Schulze, 1981) have been introduced, which substantially reduce the lower limit of detection. Because these two methods are not generally available and, especially in the case of Mossbauer spectroscopy, are rather time consuming, ordinary XRD should be adapted for quantitative estimation of Fe-oxides. Determination can be facilitated by using samples in which the Fe-oxides are concentrated by particle-size separation and a 5 M NaOH boiling treatment (Norrish & Taylor, 1961). The latter treatment is particularly suitable for kaolinitic soils as the Fe-oxides are unaffected―provided certain precautions are taken (Kaimpf & Schwertmann, 1982a). This paper gives details of a procedure for the quantitative estimation of goethite (Gt) and hematite (Hm) by XRD.

Selective extraction of amorphous iron oxides by EDTA from selected silicates and mixtures of amorphous and crystallline iron oxides

Abstract: Amorphous iron oxides in soil are often extracted by an ammonium oxalate solution (Schwertmann, 1964). This treatment may, however, also dissolve crystalline iron oxides and iron silicates (McKeague & Day, 1966; Baril & Bitton, 1969; McKeague et al., 1971; Arshad et al., 1972; Pawluk, 1972; Schwertmann, 1973; Taylor & Schwertmann, 1974; Borggaard, 1976). It has been shown that EDTA can selectively extract amorphous iron oxides from soils (Borggaard, 1979, 1981) and a synthetic mixture of amorphous iron oxide, goethite, and hematite (Borggaard, 1976). As pointed out previously (Borggaard, 1979), the EDTA method should also be tested on selected minerals to decide if it can serve as a reference method against which other less time-consuming methods may be tested.

Crystallization of Fe(III)-oxides from ferrihydrite in salt solutions; osmotic and specific ion effects

Abstract: Ferrihydrite transformed to crystalline Fe(III)-oxides in salt solutions but the degree of transformation generally decreased with increasing concentration (decreasing water activity) and haematite was favoured over goethite. More transformation occurred for chloride than for nitrate or sulphate and more for calcium than for magnesium or sodium. Calcium and magnesium favoured haematite over goethite. The results support the hypothesis that haematite not only can be formed but will be favoured over goethite in natural environments with low water activity, for instance dry or saline soils or sediments. The ionic environment modifies the general water activity effect.

Diffuse reflectance infra red spectra and ion-adsorption properties of the phosphate surface complex on goethite

Abstract: The structure of the phosphate surface compIex on goethite was investigated by means of diffuse reflectance infrared spectroscopy and Na+ and Cl- adsorption associated with phosphate adsorption was measured. The differential spectra of the phosphate surface compIex were obtained by subtracting the spectra of goethite from those of phosphated goethite. The spectrum of phosphate adsorbed on the goethite surface changed with increasing pH and this change occurred in one step over the pH range from 3.3 to 11.9. The positions of absorption bands did not change with surface coverage under similar pH conditions. Change of Na+~P/Pads. [(Na+ adsorption of phosphated goethite- Na+ adsorption of goethite)/P adsorption] with pH was closely related to the spectral change with pH. It was revealed that the PO-H bond of phosphate surface complex on goethite dissociates with increasing pH and that the dissociated phosphate adsorbs Na+. The pH of half dissociation of the PO-H bond was about 6.7 under the condition...

Technetium Behavior in Sulfide and Ferrous Iron Solutions

Abstract: Pertechnetate oxyanion (/sup 99/TcO/sub 4//sup -/), a potentially mobile species in leachate from a breached radioactive waste repository, was removed from a brine solution by precipitation with sulfide, iron, and ferrous sulfide at environmental pH's. Maghemite (..gamma..-Fe/sub 2/O/sub 3/) and goethite (..cap alpha..-FeOOH) were the dominant minerals in the precipitate obtained from the TcO/sub 4//sup -/-ferrous iron reaction. The observation of small particle size and poor crystallinity of the minerals formed in the presence of Tc suggested that the Tc was incorporated into the mineral structure after reduction to a lower valence state. Amorphous ferrous sulfide, an initial phase precipitating in the TcO/sub 4//sup -/-ferrous iron-sulfide reaction, was transformed to goethite and hematite (..cap alpha..-Fe/sub 2/O/sub 3/) on aging. The black precipitate obtained from the TcO/sub 4//sup -/-sulfide reaction was poorly crystallized technetium sulfide (Tc/sub 2/S/sub 7/) which was insoluble in both acid and alkaline solution in the absence of strong oxidants. The results suggested that ferrous- and/or sulfide-bearing groundwaters and minerals in host rocks or backfill barriers could reduce the mobility of Tc through the formation of less-soluble Tc-bearing iron and/or sulfide minerals. 12 references, 2 figures, 2 tables.

Catalytic Action of Copper on the Oxidation of Structural Iron in Vermiculitized Biotite

Abstract: The ferrous iron content of two vermiculitized biotites decreased by treatment with 0.1 N salts of copper at 70°C from 9.1–14% to 1.8–2.6%. Presumably, interlayer copper ions acted as a catalyst (here, an electron carrier) for the oxidation of iron by dissolved oxygen. The oxidized iron was ejected from the structure and formed crystalline iron minerals, such as hematite and goethite. Weight loss determinations, chemical, and X-ray powder diffraction data suggest that Cu(II) ions were polymerized to hydroxy-hydrous compounds in the interlayer space. Poor exchangeability of the resultant complex is attributed to the formation of strong electrostatic attractions between OH groups of the interlayer complexes and silicate oxygens.

Transformation of Iron-Bearing Kaolinite to Iron-Free Kaolinite, Goethite, and Hematite

Abstract: Ferruginous clay partings in limestones of the marine, largely evaporitic, Upper Triassic Mohila Formation (Makhtesh Ramon, Israel) contain hexagonal plates and cube-like bodies up to one millimeter across. Analyses by electron microscopy, infrared and Mossbauer spectroscopy, and X-ray powder diffraction indicate that the matrix contains Fe-rich anhedral kaolinite, up to 100 µm in size; the hexagonal plates are composed of euhedral, Fe-free kaolinite covered with well-developed acicular goethite and platy hematite (0.5 to 2 µm in size), and the cubes consist of fine-grained goethite with minor amounts of kaolinite. The anhedral kaolinite appears to be detrital, the hexagonal plates to be authigenic, and the cubes to be pseudomorphs after pyrite. Oxidation appears to have altered Fe-rich kaolinite and pyrite to Fe-free kaolinite, goethite, and hematite and was accompanied by recrystallization and pseudomorphic replacement. The alteration process was slow and was probably induced by a small increase in pH and in the Al/Fe ratio, resulting from oxidation of reduced components (pyrite, ferrous carbonate, organic matter) in a semiclosed, sediment-mud system. Overlying kaolinitic flint clay deposits may be the final product of a similar process.

Iron-Bearing Kaolinite in Venezuelan Laterites. II. DTA and Thermal Weight Losses of KCl and CsCl Mixtures of Laterites

Abstract: KCl and CsCl mixtures of Venezuelan laterite samples were examined by DTA. These laterites contain iron-bearing kaolinite. The first endothermic peak at ∼300°C is characteristic of goethite and gibbsite. A second endothermic peak at 470–512°C characterizes kaolinite. In KCl mixtures, the maximum of this peak decreases with increasing iron content of the kaolinite crystal. In CsCl mixtures, such a relationship is obtained only after the removal of the gibbsite from the lateritic sample. A third endothermic peak at 650–760°C is characteristic of the melting of the salt. The intensity of this peak may be used as a reference. KCl may thus serve as an internal standard for the determination of kaolinite in a series of laterite samples. CsCl, which forms a complex with kaolinite, cannot be used as an internal standard. The fourth endothermic peak results largely from the evaporation of the salt. The location of this peak in the CsCl mixtures depends on the iron content of the kaolinite. The laterite—alkali halide mixtures were subjected to weight losses at temperatures between 105 and 1000°C. In addition to the dehydroxylation processes, hydrolysis of the salts on the surfaces of kaolinite, and the evaporation of HCl take place in the CsCl mixtures and to a lesser extent in the KCl mixtures. In the CsCl mixtures, when the dehydroxylation stage of the kaolinite was studied in stages, it was found that kaolinites with a high iron content tend to lose weight mainly at a high temperature (550°C) whereas those with a low iron content tend to lose weight even at 450°C.

Transport of contaminants from energy-process-waste leachates through subsurface soils and soil components: laboratory experiments

Abstract: The subsurface transport and attenuation of inorganic contaminants common to a variety of energy process waste leachates are being studied using laboratory column methods. Anionic species currently being emphasized are As, B, Mo, and Se. Transport of the cations Cd and Ni is also being studied. The solid adsorbents consist of three soil mineral components (silica sand, kaolinite, and goethite), and four subsurface soils (a dunal sand, an oxidic sandy clay loam, an acidic clay loam, and an alkaline clay loam). Breakthrough patterns of these species from packed soil columns are followed by monitoring eluent concentrations vs time under carefully controlled laboratory conditions. This report describes the experimental methods being used, the results of preliminary batch adsorption studies, and the results of column experiments completed through calendar year 1981. Using column influent concentrations of about 10 mg/l, adsorption (mmoles/100 g) has been determined from the eluent volume corresponding to 50% breakthrough. On silica sand, kaolinite, dunal sand, and goethite, respectively, these are 2.0 x 10/sup -4/, 0.020, 0.013, and 0.31 for cadmium, 4.4 x 10/sup -4/, 0.039, 0.020, and 0.98 for nickel. On kaolinite, dunal sand, and goethite, respectively, adsorption values (mmoles/100 g) are As (0.24, 0.019, and 20.5), Bmore » (0.041, 0.0019, and 1.77), Mo (0.048, 0.0010, and 5.93), and Se (0.029, 0.00048, and 1.30). Arsenic is the most highly adsorbed contaminant species and goethite has the largest adsorption capacity of the adsorbents.« less

Aluminium substitution in goethites in soils from alluvium, Gippsland, Victoria

Abstract: The nature of the iron oxides associated with a chronosequence of soils on silty sediments in Gippsland was investigated. The soils range from 5 000 to approximately 763 000 years in age. Iron is present in the unaltered sediments, as represented by the younger soils, mainly as hematite. As the soils develop, this is replaced by goethite, which becomes more aluminous with increasing age. Thus there is continuing pedogenic development throughout the time scale investigated. In the A and B horizons of the older soils, small, coarse-sand sized hematite or maghemite concretions develop in the clay B horizons, and remain as a constituent of the light-textured A horizons as these develop through loss of the clay component of the soil by eluviation and lateral transport.

The non-existence of iron-rich magnetites

Abstract: While magnetite is known to be iron deficient at high temperature, five publications have independently claimed that iron-rich magnetites Fe3+XO4 have been observed in the range 250 to 620‡ C. The related experiments are based upon reduction of magnetite, goethite, maghemite, hematite or iron ore, and for the one of them, upon ferrous hydroxide decomposition. Another article reports an unsuccessful attempt to produce the iron-rich magnetites through hematite reduction at 535‡ C, but this temperature is considerably higher than almost all of the reduction temperatures used where iron-rich magnetite has been detected. We have therefore carried out an extensive series of experiments in order to prepare iron-rich magnetite through reductions as near as possible to the published experimental conditions. Through thermogravimetric analysis, chemical analysis, Mossbauer spectrometry and magnetic measurements, we have shown that no excess iron magnetite has been obtained. A possible explanation could be, in some cases at least, the fact that OH groups remain in the material due to preparation from solutions and annealing at moderate temperatures.

Of fe(iii) oxides from ferrihydrite in salt solutions: osmotic and specific ion effects

Abstract: A B S T R A C T : Ferrihydrite transformed to crystalline Fe(III)-oxides in salt solutions but the degree of transformation generally decreased with increasing concentration (decreasing water activity) and haematite was favoured over goethite. More transformation occurred for chloride than for nitrate or sulphate and more for calcium than for magnesium or sodium. Calcium and magnesium favoured haematite over goethite. The results support the hypothesis that haematite not only can be formed but will be favoured over goethite in natural environments with low water activity, for instance dry or saline soils or sediments. The ionic environment modifies the general water activity effect.

Aluminium Substitution in Goethites in Soils from Alluvium, Gippsland, Victoria

Abstract: The nature of the iron oxides associated with a chronosequence of soils on silty sediments in Gippsland was investigated. The soils range from 5 000 to approximately 763 000 years in age. Iron is present in the unaltered sediments, as represented by the younger soils, mainly as hematite. As the soils develop, this is replaced by goethite, which becomes more aluminous with increasing age. Thus there is continuing pedogenic development throughout the time scale investigated. In the A and B horizons of the older soils, small, coarse-sand sized hematite or maghemite concretions develop in the clay B horizons, and remain as a constituent of the light-textured A horizons as these develop through loss of the clay component of the soil by eluviation and lateral transport.

Preparation of goethite

Abstract: PURPOSE:To prepare goethite, in high productivity, at a low cost, by carrying out the usual air oxidation of an aqueous solution of a ferrous salt acidified with hydrochloric acid, in the presence of zinc ions, and heating the product after addition of excess alkali CONSTITUTION:Zimc ion is added to an aqueous solution of a ferrous salt acidified with hydrochloric acid The amount of the zinc ion is preferably 05- 5mol% of the ferrous ion The solution is subjected to the air oxidation using a nitrous acid salt or nitrogen dioxide as the catalyst, and is mixed with an alkali The amount of the alkali is slightly excess to the amount necessary for the neutralization The resultant solution is heated under atmospheric pressure to obtain a suspension, which is cooled, washed with water, filtered and dried to obtain the goethite powder

Method of manufacturing acicular goethite

Abstract: A suspension of a poorly water-soluble iron (II) containing compound in a liquid which consists substantially of water and is preferably alkaline is oxidized, to form goethite crystals and particles. The crystals and particles are filtered off, washed and dried. From a thermodynamic point of view, "more monoenergetic" particles are obtained than particles manufactured according to conventional production processes, when electrolytic oxidation processes are used, in particular, when the oxidation to goethite occurs entirely or partly by a (preferably periodic) electrolysis process. The electrolysis process may be combined with oxidation by an oxidation agent, preferably an oxidizing gas or gas mixture. Furthermore, it is possible to first oxidize the iron (II) containing compound completely to goethite by an oxidation agent, preferably an oxidizing gas or gas mixture, and to then subject the resulting suspension to an electrolytic oxidation after-treatment which preferably occurs periodically.