Showing papers on "Goethite published in 1992"

Properties and distribution of iron oxides and their association with minor elements in the soils of south‐western Australia

Abstract: SUMMARY Iron oxides from 39 soils derived from various parent materials in south-western Australia have been studied using a variety of techniques. Goethite and hematite were the only two Fe oxides present. The goethite/(goethite+hematite) ratio ranged from 0.18 to 1.0, and was highest in soils on acidic igneous rocks, decreasing for soils on alluvial and mafic parent materials. In a few soils derived from acid rocks only goethite was present. The redness rating of soils increased linearly with increasing amount of hematite. Al substitution in goethite ranged from 13 to 35 mol%, with higher values for soils on acid igneous rocks (median value = 26 mol%) than for soils on mafic (19 mol%) and alluvial (17 mol%) parent materials. Substitution of A1 in hematite ranged from 4 to 23 mol%, and was greatest in soils on mafic parent materials (median value = 12 mol% A1). A1 substitution in hematite was about half of that in associated goethite. The dehydroxylation temperature for goethite increased linearly with increasing A1 substitution. Goethite and hematite had similar crystal sizes (c. 20 nm), and both were in the form of irregular plates. Dissolution with 1 M HCl of iron oxides concentrated from the soils by 5 M NaOH digestion could be described both by the Cube Root Law and by Kabai's equation. Only one straight line was obtained for the dissolution data using Kabai's equation for samples containing both goethite and hematite, in contrast to the results of other workers. Major proportions of the Co, Cr, Cu, Mn, Ni and Zn in the soils were concentrated with the iron oxides, and the dissolution kinetics of these elements indicate that some may be present in the structure of the iron oxides.

Fast and slow phosphate sorption by goethite-rich natural materials

Abstract: Although phosphate sorption by goethite and other less-abundant Fe oxides strongly influences the concentration of this anion in the soil solution and aquatic environments, relatively little is known on the P-sorption characteristics of natural goethites. For this reason, we examined the P-sorption capacity and time course of P sorption of 10 goethite-rich soil, ferricrete and lake ore samples, in which the content and nature of mineral impurities were unlikely to affect P sorption significantly. Phosphate sorption could be adequately described by a modified Freundlich equation including a time term. The amount of P sorbed after 1 day of equilibration at a concentration of 1 mg P/liter ranged widely (0.36–2.04 /μmol P/m2). The total P sorbed after 75 days of equilibration varied less, in relative terms (1.62–3.18 μmol P/m2), i.e., a higher slow sorption tended to compensate for a lower initial (fast) sorption. Total sorbed P (X = 2.62, SD = 0.52 μmol P/m2) was similar to the sorption capacity of synthetic goethites, suggesting a common sorption mechanism and the predominance of one type of crystal face, which, according to previous transmission electron microscope observations, might be the (110). The extent of the slow reaction correlated to the ratio between micropore surface area and total surface area, as well as to oxalate-extractable Fe, which is an estimation of the ferrihydrite content. Ferrihydrite impurities might affect the slow reaction by contributing to the microporosity of some samples. Silicate adsorbed on the surface of the goethites was readily desorbed during phosphate sorption and did not significantly affect the extent of the slow sorption process.

EXAFS spectroscopic study of neptunium(V) sorption at the .alpha.-iron hydroxide oxide (.alpha.-FeOOH)/water interface

Abstract: The sorption of aqueous Np(V) on crystalline α-FeOOH (goethite) has been studied at the molecular level by synchrotron-based X-ray absorption spectroscopy. Sodium nitrate solutions (pH 7.2, ionic strength 0.08 M) having a Np(V) concentration of 1.3×10 -5 M were reacted with high surface area goethite (50 m 2 /g), resulting in ∼95% uptake of the Np and a sorption density of 10 -5 mol of Np/g of goethite

Dithionite as a dissolving reagent for goethite in the presence of EDTA and citrate; application to soil analysis

Abstract: A synergistic effect of reductant and complexant is observed in the dissolution of goethite by dithionite and citrate or EDTA. The rate data are interpreted using the surface complexation approach to describe the interface of the reacting oxide. Adsorption of both $202 (D) and complexant (L) generates =-Fe D three surface complexes that define the dissolution behavior: ~Fe-D, -~Fe-L, and dimeric -Fe L surface complexes. The initial rate increases at lower pH values because of increased surface complexation conditional formation constants. At pH values below 4, however, the fast decomposition of $20,~ gives rise to a rapid depletion of reductant, and total dissolution is not observed. It is shown that for best analytical results in soil analysis, EDTA is a better complexant than citrate; the iron extracted in one dithionite-EDTA treatment at pH 5-6, under N2 at 315 K is not increased by increasing the number of extractions, and is equivalent to the total extractable iron found by previous procedures.

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

Abstract: Color 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.

Irreversibility of sulfate sorption on goethite and hematite

Abstract: Sulfate ion adsorption and desorption experiments carried out on synthetic goethite and hematite and natural hematite show adsorption to be a highly irreversible reaction. All oxides showed an increase in sulfate ion adsorption with decrease in pH. Only a small fraction of sorbed sulfate was desorbable after 48 hr, and only at a pH of 3. Extreme irreversibility of sulfate sorption on these common soil minerals suggests that adsorbed sulfate is more immobile in watersheds than previously considered and that recovery models which inherently assume reversibility may need to be modified.

Iron oxide-clay mineral association in Brazilian Oxisols; a magnetic separation study

Abstract: Selected Brazilian Oxisols were sampled and submitted to high-gradient magnetic separation (HGMS) to study the iron oxide-clay mineral associations. The soils, derived from four different parent materials, have mineralogy dominated mostly by hematite, goethite, and kaolinite. Gibbsite appears in most soil samples. The high-gradient magnetic separation showed good separation for some soils, as indicated by color differentiation and iron oxide segregation between magnetic and nonmagnetic fractions. Soils that showed a somewhat low surface area for the iron oxides associated with high phosphate adsorption were poorly separated by HGMS. This suggests a strong interaction between kaolinite and iron oxides, which would indicate a low estimation of their surface areas obtained by the difference method using BET-N2 data. A relative concentration of anatase and rutile in the magnetic portion of some of the samples was attributed to the presence of Fe, either as coatings on the crystals or within the structure of these two minerals.

Magnetic properties of chemical remanent magnetization in synthetic and natural goethite: Prospects for a natural remanent magnetization/thermoremenant magnetization ratio paleomagnetic stability test?

Abstract: Goethite was synthesized under controlled field conditions (horizontally directed field of 0.30 mT) at 30° and 55°C with and without the presence of microfiber glass filters. Upon goethite aging from freshly precipitated ferrihydrite an inverse fabric of the magnetic susceptibility develops, more prominently for the 55°C than for the 30°C synthesis. This is compatible with the fact that for well crystalline goethite the minimum susceptibility axis coincides with the long needle axis. Scanning electron microscope (SEM) observation yielded a grain-size range from ± 0.3 μm to ± 5 μm. For the 55°C synthesis the majority of the grains are at the upper end of this range, whereas for the 30°C synthesis this is less the case. Calculation of the crystallite size from X ray line broadening revealed a range between 20 and 40 nm, indicating that the grains are polycrystalline. The magnetic properties of the resulting grain-growth chemical remanent magnetization (CRM) which parallels the inducing field, appear to be dependent on the synthesis temperature and the presence of a substrate. Specific values for the CRM range from 1 to 2.5 μA m2/kg in the presence of the microfiber glass filters. Without these filters, values are higher, up to 25 μA m2/kg. Specific values for a thermoremanent magnetization (TRM), also acquired in a 0.30 mT inducing field, are of the same order as the CRM and less than one per mil of the saturation TRM (acquired in a 2 T field) for these samples. All remanences, the 0.30 mT CRM and TRM, as well as the 2 T TRM, showed only marginal decay upon alternating field (AF) demagnetization, as expected for goethite. Thermal decay curves, obtained by routine stepwise thermal demagnetization, appeared to be very similar for all remanence types. For the 30°C synthesis series the maximum blocking temperature of the CRM and the 2 T TRM was 65°C whereas that of the 0.30 mT TRM tends to be slightly higher (∼10°C). For the 55°C synthesis series the maximum blocking temperature of all remanence types was 80–85°C. This indicates a small grain size for the polycrystalline (XRD) synthetic goethites, in agreement with SEM observations. For the 55°C synthesis series without microfiber glass filters the maximum blocking temperature was 95°C, indicating larger goethite grains. The CRM/TRM ratio decreases with increasing grain size as inferred from the maximum blocking temperature. For the 30°C series the average ratio is 1.6 (range 0.9–2.3) and for the 55°C series the average ratio is 0.56 (range 0.44–0.78), whereas a ratio of 0.17 was obtained for the sample synthesized at 55°C without substrate. To test the applicability of the CRM/TRM concept to natural rocks, that is to test whether it was possible to assign a goethite NRM as a CRM with this test, some preliminary results of goethite-bearing samples from two sites in SE France are presented. Prior to thermal demagnetization, the samples were AF demagnetized up to 100 mT fields to remove a possible low-coerciyity contribution to the NRM. At one site, BL, in a Jurassic schist, the goethite is formed by recent weathering; the NRM direction corresponds to the present-day geomagnetic field direction. At the other site, RD, in a Jurassic limestone, a recent NRM component as well as a reversed NRM component were determined, both residing in goethite. Unfortunately, the lack of a fold test hinders establishing a pretilting or posttilting age for the reversed component. The first senario would imply an Eocene age for the reversed component, while the latter would point to a Matuyama age. Also in the pretilting senario, the direction of the reversed component does not correspond with the expected Jurassic direction for stable Europe. Foi BL goetliite, NRM/TRM ratios appear to be up to 1.7, compatible with fine-grained goethite. For RD goethite, NRM/TRM ratios for die stable goethite range from 0.14 to 0.51, pointing to larger grains or better linked crystallites. A paleomagnetically unstable sample from this site has a much higher NRM/TRM ratio, in agreement with its much finer grain size. The impact of geomagnetic dipole intensity variation on the derived ratios is discussed. Extremely fine-grained natural goethite shows a remarkable low-field TRM behavior with a threefold remanence increase after AF demagnetization and storage in a field-free space for 6 days. The importance of a relatively large number of thermal demagnetization steps below 100°C to detect NRM goethite components is discussed. The observed agreement between the CRM/TRM ratio of experimental data and the NRM/TRM ratio of natural samples is encouraging. This ratio might be shown to be useful for the discrimination between stable and unstable goethite NRMs. More experimental research is necessary before the potential of the CRM/TRM technique can be fully appreciated, also for possible paleointensiy determinations. For example, the possible influence of Al, which may be incorporated in the goetliite lattice, needs to be investigated before the NRM/TRM ratio technique to assess the paleomagnetic stability of goethite can be applied to lateritic environments.

Adsorption of copper onto goethite in aqueous systems

Abstract: The adsorption of copper(II) onto goethite was studied as a function of pH, total dissolved copper concentration, surface area of goethite, and ionic strength. The adsorption of copper was similar to that of other hydrolyzable metals. A tenfold increase in goethite surface area had a significant effect on the adsorption edge, but a tenfold increase in the ionic strength of the medium did not effect the adsorption edge. The distribution coefficients increase sharply with increase in pH and ranged from 10 to 60,000 ml/g over a range of two and half pH units, depending on the goethite surface area and copper concentration. A tenfold decrease in ionic strength as well as a tenfold increase in surface area of goethite did not have any effect on the magnitude of distribution coefficients. Distribution coefficients were used to calculate the number of protons released per mole of copper adsorbed during the adsorption process. The average number of protons released per mole of copper adsorbed was estimated to be 1.40 ± 0.10.

Formation of goethite (.alpha.-FeOOH) through the oxidation of a ferrous hydroxide slurry

Abstract: The three-phase oxidation of a ferrous hydroxide slurry can produce goethite (α-FeOOH) iron oxide particles suitable for use in magnetic recording media. Experimental studies show that the apparent oxidation rate of the slurry is the rate of mass transfer of oxygen into the slurry. This result is shown to be independent of particle loading, although the slurry properties and thus the mass-transfer rate become a function of conversion as the particle loading are increased. Electron micrographs of the reaction products show that the effects of reaction rate, slurry density, and the interaction of the reaction rate and density are clearly significant in determining the particle length. However, it is also shown that there is a clear relationship between the mean particle size and the variance of the size distribution, which is insensitive to the conditions under which the particles were produced

Magnesium and ph Effect on Zinc Sorption by Goethite

Abstract: Zinc sorption by synthetic goethite (surface area 95.2 m2 g−1, pH(PZC) 7.9) was studied in equilibrium conditions as a function of Mg concentration and pH at 25°C and 1 × 10−3 M NaNO3 indifferent electrolyte. Two sets of isotherms of Zn sorption by goethite were conducted, in the absence of Mg and in the presence of 25 mg Mg L−1, each at pH 5.4, 6.2, 7.0, 7.8, and 8.5. At each pH level, the initial Zn concentration ranged from 0.025 to 7.0 mg Zn L−1 (i.e., from 3.82 × 10−7 to 1.07 × 10−4 mol Zn L−1). Magnesium effect on Zn sorption was influenced by pH and Zn levels. Magnesium reduced Zn sorption at high Zn loadings, but not at low Zn coverages, at pH 5.4, 6.2, and 7.0, while it had no effect on Zn sorption at pH 7.8 and 8.5 at any Zn coverage. Zinc sorption by goethite increased with an increase in pH; for example, Zn sorption achieved at the initial solution Zn concentration of 3.06 × 10−5 mol Zn L−1 at pH 5.4, 5.2, 7.0, 7.8, and 8.5 in the absence of Mg was, respectively, 16, 56, 107, 117, and 121 μmol Zn g−1; in the presence of 25 mg Mg L−1 it was, respectively, 11, 40, 98, 117, and 121 μmol Zn g−1. The highest Zn sorption attained in this study, 390 μmol Zn g−1 at pH 8.5, represented 16.6% coverage of the goethite surface. Zinc sorption was specific; at and below pH 7.0 it was suggested as due mainly to a mechanism of Zn diffusion into goethite lattice with subsequent fixation through possibly isomorphous substitution of lattice Fe3+ by Zn2+. Zinc sorption at pH 7.8 and 8.5 was postulated to have occurred mainly through the processes of hydrolysis and sorption of hydrolyzed Zn species plus nucleation mediated by the goethite surface.

Formation of swelling clay minerals by sulfide oxidation in some metamorphic rocks and related soils of Ontario, Canada.

Abstract: Sulfide minerals are commonly present in the metamorphic and igneous rocks of southeastern Ontario. They are also dispersed in the till that is the parent material for many soils in the area. When sulfides from these rocks are exposed to a humid atmosphere, bacteria (Thiobacillus ferrooxidans) proliferate and acid sulfate weathering proceeds rapidly with the formation of jarosite, for which K+ ions are provided by the alteration of micas and feldspar. Interstratified minerals occur as an intermediate stage during the transformation of micas towards swelling clay minerals, which are major constituents of the clay-size fraction. A similar transformation likely takes place in the soils of the area, in which swelling clay minerals are dominant. This hypothesis may be further supported by the presence of large amounts of goethite, a weathering (hydrolysis) product of jarosite. Key words: Jarosite, goethite, smectite, vermiculite, acid sulfate weathering

Crystallization of hematite and goethite in the presence of soil minerals

Abstract: 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

A silver-palladium alloy from the Bahia lateritic gold deposit, Carajas, Brazil

Abstract: A silver-palladium alloy with structural formula close to AgPd has been found in laterite from the Bahia lateritic gold deposit. The alloy occurs in a void of an iron oxide nodule, associated with goethite and hematite. The angular shape and protuberances of the alloy grains suggest crystal growth in a lateritic environment, indicating that the alloy is a secondary mineral precipitated during lateritisation. The oxidation of sulphides of the parent rocks probably favoured the migration of palladium and silver as transient thiosulphate and sulphite complexes. Destruction of the thiosulphate and sulphite ligands could result in precipitation of both palladium and silver as an alloy. Eh-pH phase diagrams for PdHzO-C1 and Ag-H20-C1 systems show that both palladium and silver are stable in lateritic environments under lower redox potentials. Such an environment may exist at the top of the ferruginous zone due to the abundant organic matter near the surface.

Magnetic properties of goethite in radulae of limpets

Abstract: Radular formation in the limpet, Acmae striata, was explored by magnetic measurements, Mossbauer spectroscopy, X-ray diffraction, and electron microscopy. It was found that, in premature radula, acicular goethite alone precipitated in the matrix-mediated manner. It grows extensively to be interlocking masses in a cusp region of detected in the porous region. A new mineral phase, hisingerite, was identified to coexist with goethite and an amorphous silicate. The goethite has a relative susceptibility of 2.5*10/sup -5/. An oxidation-reduction turned the goethite to gamma-Fe/sub 2/O/sub 3/ with a coercivity of 250 Oe and a saturation magnetization of only 6.65 emu/g due to the dilution effect of coexisting silicates. >

The availability of iron from various solid‐phase iron sources to a siderophore producing Pseudomonas strain

Abstract: Non‐crystalline or short‐range order Fe oxides (sometimes called amorphous Fe oxides) are of interest because of their surface area and high reactivity, and their influence on Fe availability in the soil Eight non‐crystalline Fe(III) oxides were precipitated from solutions with Si/Fe(III) molar ratios ranging from 000 to 100 These eight Fe oxides, along with goethite and hematite, were evaluated for their ability to supply Fe to an isolate of Pseudomonas obtained from grass roots Levels of siderophore in solution were significantly higher in controls (with no Fe added) and in the presence of hematite or the more‐crystalline goethite sample, than with the non‐crystalline oxide treatments The non‐crystalline oxides were indistinguishable in their ability to suppress siderophore production Greater numbers of Pseudomonas were observed in cultures amended with the non‐crystalline oxides than in the cultures amended with crystalline oxides or in the Fe‐deficient controls

A Mössbauer study of an impactite from the Monturaqui crater

Abstract: The iron mineralogy of samples of the Monturaqui impactite has been studied by Mossbauer spectroscopy Magnetite, maghemite, goethite and a ferrous glass phase were identified In a magnetic separate a bcc-structured iron-nickel alloy was identified in addition to the oxide phases The oxides have formed by weathering of iron-nickel alloys

Wpływ przeobrażeń mineralnych na składchemiczny wód w strefie wietrzenia łupków pirytonośnych w Wieściszowicach, Rudawy Janowickie, Sudety Zachodnie, Polska

Abstract: The effects of mineral alterations on the chemical composition of waters in the weathered zone of pyrite-bearing schists in Wieściszowice, Rudawy Janowickie Mts., W Sudetes, Poland Chemical composition of waters, mineralogical studies and calculations using WATEQF program were the basis of determining the origin of water components as, well as the course of geochemical alterations in oxidation zone of pyrite-bearing schist deposit in Wieściszowice (Rudawy Janowickie Mts., SW Poland). Chlorite, sericite, quartz of detrital origin, illite, kaolinite, goethite, as well as supergene sulfate minerals (gypsum, copiapite, pickeringite, fibroferrite, slavikite, alunogene and epsomite) were identified in the abandoned pyrite open-pit mine. Waters of SO(4)-Ca-Mg type, showing pH range 5,3-2,8 and total dissolved solids content from 124 mg/1 to 3366 mg/1 were found in the area studied. Distinct enrichment in Fe, Al, Mn, Cu, Zn, Ni, as well as low K and Na concentrations arc characteristic of waters contacting for longer time with the material of oxidation zone. Clay minerals (illite, kaolinite, montmorillonite) control the solubility of Si, Al, Na, and K in waters showing pH=4,0 - 5,3. In strongly acid environment (pH below 3), the solubility of silica is controlled by amorphous silica whilst that of aluminium - by sulfate minerals. Gypsum determines calcium concentracions in waters, whereas goethite and iron sulfates - those of iron.