Showing papers on "Goethite published in 2012"
TL;DR: Measurements of specific rates of iron oxidation and reduction by acidophilic microorganisms show that different species vary in their capacities for iron oxido-reduction, and that this is influenced by the electron donor provided and growth conditions used.
Abstract: Many different species of acidophilic prokaryotes, widely distributed within the domains Bacteria and Archaea, can catalyze the dissimilatory oxidation of ferrous iron or reduction of ferric iron, or can do both. Microbially-mediated cycling of iron in extremely acidic environments (pH <3) is strongly influenced by the enhanced chemical stability of ferrous iron and far greater solubility of ferric iron under such conditions. Cycling of iron has been demonstrated in vitro using both pure and mixed cultures of acidophiles, and there is considerable evidence that active cycling of iron occurs in acid mine drainage streams, pit lakes and iron-rich acidic rivers, such as the Rio Tinto. Measurements of specific rates of iron oxidation and reduction by acidophilic microorganisms show that different species vary in their capacities for iron oxido-reduction, and that this is influenced by the electron donor provided and growth conditions used. These measurements, and comparison with corresponding data for oxidation of reduced sulfur compounds, also help explain why ferrous iron is usually used preferentially as an electron donor by acidophiles that can oxidize both iron and sulfur, even though the energy yield from oxidizing iron is much smaller than that available from sulfur oxidation. Iron-oxidizing acidophiles have been used in biomining (a technology that harness their abilities to accelerate the oxidative dissolution of sulfidic minerals and thereby facilitate the extraction of precious and base metals) for several decades. More recently they have also been used to simultaneously remediate iron-contaminated surface and ground-waters and produce a useful mineral by-product (schwertmannite). Bioprocessing of oxidized mineral ores using acidophiles that bring about the reductive dissolution of ferric iron minerals such as goethite has also recently been demonstrated, and new biomining technologies based on this approach are being developed.
328 citations
TL;DR: In this paper, the authors report on the use of synthetic and natural Fe (hydr)oxides as catalysts in environmental remediation procedures using an advanced oxidation process, more specifically the Fentonlike system, which is highly efficient in generating reactive species such as hydroxyl radicals, even at room temperature and under atmospheric pressure.
Abstract: Iron is the fourth most common element by mass in the Earth’s crust and forms compounds in several oxidation states. Iron (hydr)oxides, some of which form inherently and exclusively in the nanometre-size range, are ubiquitous in nature and readily synthesized. These facts add up to render many Fe (hydr)oxides suitable as catalysts, and it is hardly surprising that numerous studies on the applications of Fe (hydr)oxides in catalysis have been published. Moreover, the abundant availability of a natural Fe source from rocks and soils at minimal cost makes the potential use of these as heterogeneous catalyst attractive.
Besides those Fe (hydr)oxides that are inherently nanocrystalline (ferrihydrite, Fe5HO8·4H2O, and feroxyhyte, δ′-FeOOH), magnetite (Fe3O4) is often used as a catalyst because it has a permanent magnetization and contains Fe in both the divalent and trivalent states. Hematite, goethite and lepidocrocite have also been used as catalysts in their pure forms, doped with other cations, and as composites with carbon, alumina and zeolites among others.
In this review we report on the use of synthetic and natural Fe (hydr)oxides as catalysts in environmental remediation procedures using an advanced oxidation process, more specifically the Fenton-like system, which is highly efficient in generating reactive species such as hydroxyl radicals, even at room temperature and under atmospheric pressure. The catalytic efficiency of Fe (hydr)oxides is strongly affected by factors such as the Fe oxidation state, surface area, isomorphic substitution of Fe by other cations, pH and temperature.
311 citations
TL;DR: In this paper, a study was conducted to evaluate hematite, magnetite, goethite, and iron rich laterite soil as arsenic adsorbents, and the results showed that arsenic adsorption occurred over the entire pH range tested (pH 4 − 11).
226 citations
TL;DR: The findings emphasize the importance of solution speciation in metal isotope sorption studies and suggest that the dissolved Hg(II) pool in soils and sediments, which is the most mobile and bioavailable, should be isotopically heavy, as light Hg isotopes are preferentially sequestered during binding to both mineral phases and natural organic matter.
Abstract: The application of Hg isotope signatures as tracers for environmental Hg cycling requires the determination of isotope fractionation factors and mechanisms for individual processes. Here, we investigated Hg isotope fractionation of Hg(II) sorption to goethite in batch systems under different experimental conditions. We observed a mass-dependent enrichment of light Hg isotopes on the goethite surface relative to dissolved Hg (e(202)Hg of -0.30‰ to -0.44‰) which was independent of the pH, chloride and sulfate concentration, type of surface complex, and equilibration time. Based on previous theoretical equilibrium fractionation factors, we propose that Hg isotope fractionation of Hg(II) sorption to goethite is controlled by an equilibrium isotope effect between Hg(II) solution species, expressed on the mineral surface by the adsorption of the cationic solution species. In contrast, the formation of outer-sphere complexes and subsequent conformation changes to different inner-sphere complexes appeared to have insignificant effects on the observed isotope fractionation. Our findings emphasize the importance of solution speciation in metal isotope sorption studies and suggest that the dissolved Hg(II) pool in soils and sediments, which is the most mobile and bioavailable, should be isotopically heavy, as light Hg isotopes are preferentially sequestered during binding to both mineral phases and natural organic matter.
137 citations
125 citations
TL;DR: In this paper, a one-step synthesis of a nanocomposite of goethite (α-FeOOH) nanorods and reduced graphene oxide (RGO) using a solution method was reported.
118 citations
TL;DR: In this paper, the authors examined the competitive retention of As on goethite and birnessite using a Donnan reactor, where each oxide is isolated by a semi-permeable membrane through which arsenic can migrate.
117 citations
TL;DR: The results demonstrate that structurally incorporated trace elements are mobilized from iron oxides into fluids without abiotic or microbial net iron reduction.
Abstract: Electron transfer and atom exchange (ETAE) between aqueous Fe(II) and Fe(III) oxides induces surface growth and dissolution that affects trace element fate and transport. We have recently demonstrated Ni(II) cycling through goethite and hematite (adsorbed Ni incorporates into the mineral structure and preincorporated Ni releases to solution) during Fe(II)-Fe(III) ETAE. However, the chemical parameters affecting net trace element release remain unknown. Here, we examine the chemical controls on Ni(II) and Zn(II) release from Ni- and Zn-substituted goethite and hematite during reaction with Fe(II). Release follows a rate law consistent with surface reaction limited mineral dissolution and suggests that release occurs near sites of Fe(III) reductive dissolution during Fe(II)-Fe(III) ETAE. Metal substituent type affects reactivity; Zn release is more pronounced from hematite than goethite, whereas the opposite trend occurs for Ni. Buildup of Ni or Zn in solution inhibits further release but this resumes upon fluid exchange, suggesting that sustained release is possible under flow conditions. Mineral and aqueous Fe(II) concentrations as well as pH strongly affect sorbed Fe(II) concentrations, which directly control the reaction rates and final metal concentrations. Our results demonstrate that structurally incorporated trace elements are mobilized from iron oxides into fluids without abiotic or microbial net iron reduction. Such release may affect micronutrient availability, contaminant transport, and the distribution of redox-inactive trace elements in natural and engineered systems.
113 citations
TL;DR: Inherently formed iron-based water treatment residuals (WTRs) were tested as alternative sorbents for multi-heavy metal removal from synthetic solutions, contaminated sediments, and surface waters.
107 citations
TL;DR: In this paper, changes in Ni speciation in a 64m vertical profile of a New Caledonian saprolitic-lateritic regolith developed over ultramafic rocks under tropical weathering conditions were investigated by EXAFS spectroscopy.
105 citations
TL;DR: In this article, three coal mine drainage (CMD) sites in central Pennsylvania were studied to determine similarities in sediment composition, mineralogy, and morphology, and the mineralogy of the three iron mounds was very similar.
TL;DR: The results show that electron transfer between aqueous Fe(II) and solid Fe(III) in goethite can occur under wide range of geochemical conditions, but that the extent of redox-driven Fe atom exchange may be dependent on the presence of substituting cations such as Al.
Abstract: The reaction of Fe(II) with Fe(III) oxides and hydroxides is complex and includes sorption of Fe(II) to the oxide, electron transfer between sorbed Fe(II) and structural Fe(III), reductive dissolution coupled to Fe atom exchange, and, in some cases mineral phase transformation. Much of the work investigating electron transfer and atom exchange between aqueous Fe(II) and Fe(III) oxides has been done under relatively simple aqueous conditions in organic buffers to control pH and background electrolytes to control ionic strength. Here, we investigate whether electron transfer is influenced by cation substitution of Al(III) in goethite and the presence of anions such as phosphate, carbonate, silicate, and natural organic matter. Results from 57Fe Mossbauer spectroscopy indicate that both Al-substitution (up to 9%) and the presence of common anions (PO43-, CO32-, SiO44-, and humic acid) does not inhibit electron transfer between aqueous Fe(II) and Fe(III) in goethite under the conditions we studied. In contras...
TL;DR: The molecular-scale immobilization mechanisms of uranium uptake in the presence of phosphate and goethite were examined by extended X-ray absorption fine structure (EXAFS) spectroscopy and revealed that the precipitated U(VI) had a structure consistent with the meta-autunite group of solids.
Abstract: The molecular-scale immobilization mechanisms of uranium uptake in the presence of phosphate and goethite were examined by extended X-ray absorption fine structure (EXAFS) spectroscopy. Wet chemistry data from U(VI)-equilibrated goethite suspensions at pH 4–7 in the presence of ∼100 μM total phosphate indicated changes in U(VI) uptake mechanisms from adsorption to precipitation with increasing total uranium concentrations and with increasing pH. EXAFS analysis revealed that the precipitated U(VI) had a structure consistent with the meta-autunite group of solids. The adsorbed U(VI), in the absence of phosphate at pH 4–7, formed bidentate edge-sharing, ≡Fe(OH)2UO2, and bidentate corner-sharing, (≡FeOH)2UO2, surface complexes with respective U–Fe coordination distances of ∼3.45 and ∼4.3 A. In the presence of phosphate and goethite, the relative amounts of precipitated and adsorbed U(VI) were quantified using linear combinations of the EXAFS spectra of precipitated U(VI) and phosphate-free adsorbed U(VI). A U...
TL;DR: The green rusts are found to be much more abundant in corrosion scales than it has been assumed so far and the most abundant was carbonate green rust GR(CO(3)(2-))(I).
TL;DR: The adsorption to goethite of extracellular polymeric substances (EPS) isolated from Pseudomonas putida was investigated and it was demonstrated phosphate groups of EPS can form monodentate inner-sphere complexes at lower pH 3.0, while form bidentateinner-spheres complexes at higher pH 9.0.
TL;DR: In this article, the authors used a CSIRO Hy-Logging™ system from 180 reverse circulation and 14 diamond drill cores spanning a depth from surface to 55 m below surface, intersecting the Rocklea deposit.
Abstract: Visible-near to shortwave infrared reflectance spectra (VNIR-SWIR—400–2,500 nm wavelength region) provide quantitative measurements of mineral abundances and mineral physicochemistries from drill core samples of channel iron ore. The infrared spectral reflectance measurements of drill core samples from the Rocklea channel iron deposit, located in the Hamersley Basin of Western Australia, were validated against X-ray flouresence (XRF) and X-ray diffraction (XRD). The reflectance data were collected using a CSIRO Hy-Logging™ system from 180 reverse circulation and 14 diamond drill cores spanning a depth from surface to 55 m below surface, intersecting the Rocklea deposit. The mineralogy of this channel iron deposit comprises chiefly goethite (both vitreous and ochreous forms) with lesser amounts of hematite and variable amounts of quartz, kaolinite, smectite (both dioctahedral and trioctahedral varieties), and carbonate (both dolomite and calcite). Iron ore and waste rock mineralogy were extracted from the infrared spectroscopic reflectance data using the geometry (depth/wavelength) of continuum-removed reflectance spectra, with depths of absorption features proportional to mineral abundance and wavelength positions proportional to chemical composition. For any one mineral, a number of its diagnostic spectral features are used to determine its mineral abundance and composition, in order to avoid complications with minerals that spectrally overlap with part of the diagnostic spectral features of the mineral of interest. This method that combines multiple spectral features to identify and quantify minerals is transferable to all types of infrared reflectance spectroscopic data collected from drill core to satellites. Final products include: iron (oxyhydr-)oxide content (root mean square error (RMSE) 9.1 wt % Fe); Al clay content (RMSE 3.9 wt % Al 2 O 3 ); hematite/goethite ratio (RMSE 9.0 wt % goethite); vitreous versus ochreous goethite (not easily measured using other analytical techniques); clay mineral type (kaolinite, montmorillonite and nontronite); and carbonate composition (dolomite vs. calcite). The Rocklea infrared reflectance spectroscopy-based mineral abundance and composition results have been used in an associated study to characterize the architecture of the Rocklea channel iron deposit, with implications for exploration, mining, and ore genesis.
TL;DR: The modeling approach successfully predicts U(VI) adsorption behavior by the background F-Area sediments, and the experimental results indicate that the fine fractions in sediments control U( VI) Adsorption due to their large surface area, although the quartz sands show a stronger adsorptive ability per unit surface area than thefine fractions at pH < 5.0.
Abstract: The mobility of an acidic uranium waste plume in the F-Area of Savannah River Site is of great concern. In order to understand and predict uranium mobility, U(VI) adsorption experiments were performed as a function of pH using background F-Area aquifer sediments and reference goethite and kaolinite (major reactive phases of F-Area sediments), and a component-additivity (CA) based surface complexation model (SCM) was developed. Our experimental results indicate that the fine fractions (≤45 μm) in sediments control U(VI) adsorption due to their large surface area, although the quartz sands show a stronger adsorption ability per unit surface area than the fine fractions at pH 4.0. Our CA model combines an existing U(VI) SCM for goethite and a modified U(VI) SCM for kaolinite along with estimated relative surface area abundances of these component minerals. The modeling approach successfully predicts ...
TL;DR: Results suggested that in the oxic environment ferrous iron, which formed via the photoinduced oxidation of As(III) in the presence of goethite, was heterogeneously oxidized to ferric iron by dissolved oxygen.
Abstract: The photochemistry of an aqueous suspension of goethite in the presence of arsenite (As(III)) was investigated with X-ray absorption near edge structure (XANES) spectroscopy and solution-phase analysis. Irradiation of the arsenite/goethite under conditions where dissolved oxygen was present in solution led to the presence of arsenate (As(V)) product adsorbed on goethite and in solution. Under anoxic conditions (absence of dissolved oxygen), As(III) oxidation occurred, but the As(V) product was largely restricted to the goethite surface. In this circumstance, however, there was a significant amount of ferrous iron release, in stark contrast to the As(III) oxidation reaction in the presence of dissolved oxygen. Results suggested that in the oxic environment ferrous iron, which formed via the photoinduced oxidation of As(III) in the presence of goethite, was heterogeneously oxidized to ferric iron by dissolved oxygen. It is likely that aqueous reactive oxygen species formed during this process led to the fur...
TL;DR: The presence of dissolved silica at concentrations comparable to those encountered in natural waters decreases the reactivity of iron minerals toward H(2)O(2), because silica adsorbs onto the surface of Iron minerals and alters catalytic sites, and should be considered in the design of H( 2)O (2)-based treatment systems.
Abstract: The decomposition of H2O2 on iron minerals can generate •OH, a strong oxidant that can transform a wide range of contaminants. This reaction is critical to In Situ Chemical Oxidation (ISCO) processes used for soil and groundwater remediation, as well as advanced oxidation processes employed in waste treatment systems. The presence of dissolved silica at concentrations comparable to those encountered in natural waters decreases the reactivity of iron minerals toward H2O2, because silica adsorbs onto the surface of iron minerals and alters catalytic sites. At circumneutral pH values, goethite, amorphous iron oxide, hematite, iron-coated sand, and montmorillonite that were pre-equilibrated with 0.05–1.5 mM SiO2 were significantly less reactive toward H2O2 decomposition than their original counterparts, with the H2O2 loss rates inversely proportional to SiO2 concentrations. In the goethite/H2O2 system, the overall •OH yield, defined as the percentage of decomposed H2O2 producing •OH, was almost halved in the ...
TL;DR: In this article, the effect of pH on the sorption of various soil minerals was investigated through batch experiments, and it was shown that the effect was predominant compared to that of ionic strength in removing high concentrations of ibuprofen from aqueous solution.
Abstract: Pharmaceuticals have gained significant attention in recent years due to the environmental risks posed by their versatile application and occurrence in the natural aquatic environment. The transportation and distribution of pharmaceuticals in the environmental media mainly depends on their sorption behavior in soils, sediment–water systems and waste water treatment plants, which varies widely across pharmaceuticals. Sorption of ibuprofen, a non-steroidal anti-inflammatory drug, onto various soil minerals, viz., kaolinite, montmorillonite, goethite, and activated carbon, as a function of pH (3–11), ionic strength (NaCl concentration: 0.001–0.5 M), and the humic acid concentration (0–1,000 mg/L) was investigated through batch experiments. Experimental results showed that the sorption of ibuprofen onto all sorbents was highest at pH 3, with highest sorption capacity for activated carbon (28.5 mg/g). Among the minerals, montmorillonite sorbed more ibuprofen than kaolinite and goethite, with sorption capacity increasing in the order goethite (2.2 mg/g) < kaolinite (3.1 mg/g) < montmorillonite (6.1 mg/g). The sorption capacity of the selected minerals increased with increase in ionic strength of the solution in acidic pH condition indicating that the effect of pH was predominant compared to that of ionic strength. An increase in humic acid concentration from low to high values made the sorption phenomena very complex in the soil minerals. Based on the experimental observations, montmorillonite, among the selected soil minerals, could serve as a good candidate to remove high concentrations of ibuprofen from aqueous solution.
Book•
07 Nov 2012
TL;DR: In this paper, the authors investigated the effect of organic matter, iron, and aluminium on soil structural stability and found that organic matter was more likely to react positively to iron and aluminium at the solid-water interface.
Abstract: Part I: Reactivity and Transformations of Mineral Constituents and Metals at the soil-solution interfaces. 1. Sorption mechanisms at the solid-water interface Ph. Behra, et al. 2. Comparison between bacterial and chemical dissolution of Al-substituted goethite. Incidence on mobilization of iron N. Bousserrhine, et al. 3. Preparation and thermodynamic equilibria of green rusts in aqueous solutions and their identification as mineral in hydromorphic soils J.-M.R. Genin, et al. 4. An XPS and AFM coupled study of air and bio-oxydized pyrite surfaces V. Toniazzo, et al. 5. Transformation of iron-containing minerals in kaolin during growth of a mixed bacterial culture derived from kaolin E.S. Shelobolina, et al. 6. Effect of succinic acid produced by microorganisms and plant roots on copper sorption by soil T. Pampura, M. Ustinin. 7. Interaction of iron and organic matter in relation to its uptake by plants A.M. Elgala. 8. Effects of organic matter, iron and aluminium on soil structural stability M. Arias, et al. 9. Interactions of mugineic acid with allophane, imogolite, montmorillonite and gibbsite S. Iridate, K. Inoue. 10. Aluminium speciation, toxicity and transfer from soils to surface waters in two contrasting watersheds exposed to acid deposition in the Vosges Mountains (North-Eastern France) O. Maitat, et al. 11. Ultrafiltration as a means to investigate copper resistance mechanisms in soil bacteria I. Lamy, et al. Part II: Nature, Dynamics and Transformations of Organic Compounds and Enzymes in Soils. 12. Application of organicgeochemistry techniques to environmental problems P. Faure, et al. 13. In situ ATR-FTIR characterization of organic macromolecules aggregated with metallic cations F. Quile, et al. 14. The structure of organic nitrogen in particle size fractions determined by 15N CPMAS NMR H. Knicker, et al. 15. Polymerization: a possible consequence of copper-phenolic interactions A. Oess, et al. 16. Effect of pH, Exchange Cations and Hydrolitic Species of Al and Fe on Formation and Properties of Montmorillonite-Protein Complexes A. De Cristofaro, et al. 17. Adsorption and properties of urease immobilized on several iron, and aluminium oxides (hydroxides) and kaolinite Q. Huang, et al. 18. The fate of acid phosphatase in the presence of phenolic substances, biotic and abiotic catalysts M.A. Rao, et al. 19. Kinetics of catechol oxidation catalyzed by tyrosinase or d-MnO2 A. Naidja, et al. 20. Plant residue decomposition: effect of soil porosity and particle size L. Fruit, et al. 21. The effect of humic substances from oxyhumolite on plant development S.S. Gonet, et al. 22. Changes in some properties of humic substances from Melanudands induced by vegetational succession from grass to deciduous trees T. Higashi, et al. 23. Characterization of the organic substances in reclaimed soils L. Petrova, et al. Part III: Microorganism-Colloid Interactions and their Effect on Bioavailability of Pollutants and Nutrients in Terrestrial and Freshwater Environments. 24. Interactions between polychlorinated bip
TL;DR: In this paper, the effects of reaction time, nitrate concentration, iron-to-nitrate ratio on nitrate removal rate over nanoscale zero-valent iron (NZVI)-H and NZVI-N were investigated.
Dissertation•
11 Apr 2012
TL;DR: In this paper, the grain-size dependent behavior of natural goethite, pyrrhotite, and hematite was investigated and the results showed that the grain size-dependent behavior of such parameters is poorly known.
Abstract: The increasing importance of sediments for paleomagnetic research
prompted a study of rockmagnetic parameters of natural goethite, pyrrhotite
and hematite. Grain-size dependent behaviour of such parameters is
poorly known for goethite and pyrrhotite as well as for fine-grained
hematite. Data of hematite indicate a complex rockmagnetic behaviour.
Existing data seem to be contradictory in many aspects. The rockmagnetic
parameters reported in the present thesis for the natural goethite and
pyrrhotite samples comprise twelve grain-size fractions from 250 micrometer
down to <5 micrometer. For the natural hematite sample, which has
a low-temperature origin, the <5 micrometer fraction was divided into
six grain-size fractions down to <0.25 micrometer.
TL;DR: In this paper, the authors describe the abiotic mineralogical transformation of ferrihydrite (F), goethite (G), and hematite (H) into mixed Fe II -Fe III green rust (GR).
TL;DR: Results indicated a good reproducibility of quantitative total iron determinations by the ferrozine and phenanthroline assays for easily soluble iron forms such as Fe(II)((aq)), Fe(III)( (aq)), mixed valence solutions, and ferrihydrite.
TL;DR: Goethite nanoparticles synthesized using hydrazine sulfate as a modifying agent were evaluated for As(V) adsorption capacity in this article, where the nanoparticles were characterized for their morphological and structural features.
Abstract: Goethite nanoparticles synthesized using hydrazine sulfate as a modifying agent were evaluated for As(V) adsorption capacity. The nanoparticles were characterized for their morphological and structural features. The precipitated goethite particles were spherical with particle size of less than 10 nm. Batch adsorption study was carried out systematically varying parameters such as pH, contact time, initial As(V) concentration and adsorbent doses. The Langmuir isotherm represented the equilibrium data well and the estimated monolayer adsorption capacity at ambient temperature was 76 mg/g, which is significantly higher than most of the adsorbents reported in the literature. Adsorption kinetic data were better represented by the pseudo-second order kinetic model. Intra-particle diffusion played a significant role in the rate controlling process in the initial hour. Desorption study showed that the loaded adsorbent could be regenerated when treated with dilute sodium hydroxide solution of pH 13.
TL;DR: The fast Fe(III) reduction made the peat soils particularly vulnerable to changes in redox conditions, however, the precipitation of vivianite/metavivianites minerals may control soluble P(i) concentrations to between 2 and 3 μM in the long term if the soil is not disturbed.
Abstract: Phosphorus retention in lowland soils depends on redox conditions. The aim of this study was to evaluate how the Fe(III) reduction degree affects phosphate adsorption and precipitation. Two similarly P-saturated, ferric Fe-rich lowland soils, a sandy and a peat soil, were incubated under anaerobic conditions. Mossbauer spectroscopy demonstrated that Fe(III) in the sandy soil was present as goethite and phyllosilicates, whereas Fe(III) in the peat soil was mainly present as polynuclear, Fe-humic complexes. Following anoxic incubation, extensive formation of Fe(II) in the solids occurred. After 100 d, the Fe(II) production reached its maximum and 34% of the citrate-bicarbonate-dithionite extractable Fe (Fe(CBD)) was reduced to Fe(II) in the sandy soil. The peat soil showed a much faster reduction of Fe(III) and the maximum reduction of 89% of Fe(CBD) was reached after 200 d. Neoformation of a metavivianite/vivianite phase under anoxic conditions was identified by X-ray diffraction in the peat. The sandy soil exhibited small changes in the point of zero net sorption (EPC₀) and P(i) desorption with increasing Fe(III) reduction, whereas in the peat soil P desorption increased from 80 to 3100 μmol kg⁻¹ and EPC₀ increased from 1.7 to 83 μM, after 322 d of anoxic incubation. The fast Fe(III) reduction made the peat soils particularly vulnerable to changes in redox conditions. However, the precipitation of vivianite/metavivianite minerals may control soluble P(i) concentrations to between 2 and 3 μM in the long term if the soil is not disturbed.
TL;DR: This work shows that redox-sensitive elements structurally incorporated within iron oxides are reduced and repartitioned into fluids during Fe(II)-mediated recrystallization of Cu-, Co-, and Mn-substituted goethite and hematite.
Abstract: The reduction of trace elements and contaminants by Fe(II) at Fe(III) oxide surfaces is well documented. However, the effect of aqueous Fe(II) on the fate of redox-active trace elements structurally incorporated into iron oxides is unknown. Here, we investigate the fate of redox-active elements during Fe(II)-activated recrystallization of Cu-, Co-, and Mn-substituted goethite and hematite. Enhanced release of Cu, Co, and Mn to solution occurs upon exposure of all materials to aqueous Fe(II) relative to reactions in Fe(II)-free fluids. The quantity of trace element release increases with pH when Fe(II) is present but decreases with increasing pH in the absence of Fe(II). Co and Mn release from goethite is predicted well using a second-order kinetic model, consistent with the release of redox-inactive elements such as Ni and Zn. However, Cu release and Co and Mn release from hematite require the sum of two rates to adequately model the kinetic data. Greater uptake of Fe(II) by Cu-, Co-, and Mn-substituted iron oxides relative to analogues containing only redox-inactive elements suggests that net Fe(II) oxidation occurs. Reduction of Cu, Co, and Mn in all materials following reaction with Fe(II) at pHs 7.0-7.5 is confirmed by X-ray absorption near-edge structure spectroscopy. This work shows that redox-sensitive elements structurally incorporated within iron oxides are reduced and repartitioned into fluids during Fe(II)-mediated recrystallization. Such abiotic reactions likely operate in tandem with partial microbial and abiotic iron reduction or during the migration of Fe(II)-containing fluids, mobilizing structurally bound contaminants and micronutrients in aquatic systems.
TL;DR: In this article, the authors examined both spectroscopic and traditional mining data from 180 drill holes through the Rocklea channel iron deposit in the Hamersley region of Western Australia.
Abstract: This study demonstrates how mineralogy generated from spectroscopic visible, near, and shortwave infrared reflectance data, collected using rapid drill core logging systems, can be used to build one-, two- and three-dimensional models of the architecture of ore systems, with applications toward exploration and mining. In particular, this study examines both spectroscopic and traditional mining data (laboratory geochemistry and field geologist logging) from 180 drill holes through the Rocklea channel iron deposit in the Hamersley region of Western Australia. Valuable infrared reflectance spectroscopy-based mineralogy includes: the types and abundances of iron (oxyhydr-)oxides (hematite, vitreous goethite, and ochreous goethite); clays (well- and poorly ordered kaolin, Al and Fe smectite); and carbonates (calcite and dolomite). Algorithms to determine the abundance and composition of these minerals from infrared reflectance spectra were validated in an associated study by Haest et al. (2012) and were found to be accurate (e.g., root mean square error (RMSE) for Fe (oxyhydr-)oxide abundance prediction of 9.1 wt % Fe). Petrographic analysis and validated infrared reflectance spectroscopy-based mineralogy constrained the stratigraphy in the paleochannel and the paragenetic history of each horizon. The Rocklea channel iron deposit developed over weathered basalt and metasedimentary rocks, with an internal channel stratigraphy dominated from bottom to top by the following: (1) well-ordered (in situ) kaolinite and a partially denaturated channel iron deposit, (2) poorly ordered (transported) kaolinite, (3) ochreous goethite with scarce ooidal textures, no clays, and late-stage vitreous goethite/silica replacement, (4) mostly poorly ordered kaolinite, and (5) calcrete with associated Fe smectite.
The mineral paragenesis of the Rocklea deposit was compared against current models for channel iron deposit formation. A key finding is the relationship between parent rock composition, superimposed regolith cover, and channel iron deposit ore quality, which are linked through ground-water interactions and the physicochemistries of both the parent rock and the deposit. This has implications for both exploration and ore deposit characterization: (1) ore-grade channel iron deposits can develop several kilometers downstream (50 km, in this case) from the proposed source rock areas above mafic volcanics and metasediments, (2) vitreous goethite, calcrete, Al and Fe smectite cover the Rocklea deposit and are proposed as potential vectors to channel iron deposit mineralization at depth, (3) improved mineralogy from hyperspectral data in terms of iron (oxyhydr-) oxide and clay content/composition can improve iron ore resource delineation, iron ore processing (separation of vitreous and ochreous goethite), and pit design (differentiating “swelling” smectite (requiring pit walls with lower slopes) from kaolin or white mica).
01 Feb 2012
TL;DR: At all pH values studied the band associated with hydrogen bonding was more intense for the adsorbed species than in solution at the corresponding pH indicating that hydrogen bonding plays an important role in binding IP(6) to goethite.
Abstract: Adsorption of inositol hexaphosphate (IP 6 ) on goethite has been studied as a function of pH and concentration, and by use of Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR). While adsorption was highest at low pH, a significant amount remained adsorbed above pH 10 where, in the absence of IP 6 , the surface is expected to have a net negative charge. The adsorption isotherm at pH 5.5 indicated strong binding to the surface with each adsorbed species occupying about 2.5 nm 2 . ATR-FTIR spectra of IP 6 solutions in the pH range from 2 to 12 were fitted with a single set of IR bands which were assigned primarily by analogy with phosphate spectra. From its variation in intensity with pH the band at 1040 cm −1 was assigned to the effect of hydrogen bonding on the P O vibration. No additional bands were required to fit the spectra of IP 6 adsorbed to goethite, indicating that adsorption occurs by outer-sphere complexation in this system. At all pH values studied the band associated with hydrogen bonding was more intense for the adsorbed species than in solution at the corresponding pH indicating that hydrogen bonding plays an important role in binding IP 6 to goethite.