Goethite Particles Research Articles

Infrared and Mössbauer studies of iron in aluminosilicate glasses

Samples of 10Fe 2O 3·10Al 2O 3·80SiO 2 composition were prepared by the sol–gel method and heat-treated between 120 and 1300 °C under oxidising (air) conditions. These samples were studied by Fourier transformer infrared (FTIR) and Mössbauer spectroscopy. The results indicate that Fe 3+ is in octahedral sites at 250 °C and in tetrahedral sites between 500 and 1300 °C. Goethite and hematite particles are present in the 250 and 500 °C samples and hematite particles in the samples heat-treated between 1000 and 1300 °C. The hematite particles, present in the samples, show a lower hyperfine field (47.91±0.08 T) than that usually seen for hematite (51.5 T). This is due to the fact of Al 3+ ions take the place of Fe 3+ ions in hematite particles.

The Interaction of Prussian Blue and Dissolved Hexacyanoferrate Ions with Goethite (α-FeOOH) Studied to Assess the Chemical Stability and Physical Mobility of Prussian Blue in Soils

Colloidal Prussian blue and dissolved hexacyanoferrate ions strongly interact with the surface of goethite (α-FeOOH) particles. Whereas Prussian blue is deposited on the surface of goethite as a solid phase with all the properties typical of solid Prussian blue, the hexacyanoferrate ions form initially a layer of surface bound hexacyanoferrate ions, which exhibit properties intermediate between those of free hexacyanoferrate ions and hexacyanoferrate ions bound in Prussian blue. The products of interaction of goethite with Prussian blue and hexacyanoferrate ions were studied by voltammetry of immobilized microcrystals, infrared spectrometry, Vis diffuse reflection spectrometry, transmission electron microscopy, and ESR spectroscopy. The kinetics of Prussian blue destruction was measured by solution Vis spectrometry and also by voltammetry of solid microcrystals. The remarkable stability of Prussian blue in soils can be explained by its strong adherence as a solid phase to iron oxides and oxide hydroxides in soils. This prevents the formation of soluble colloids of Prussian blue. It does not prevent the hydrolysis of Prussian blue to iron oxide hydroxides and hexacyanoferrate(II) ions at elevated pH which proceeds at almost the same rate as that of pure Prussian blue colloid. Even when this hydrolysis of Prussian blue occurs, it is the hexacyanoferrate(II) that is effectively adsorbed on the surface of iron oxide hydroxides, again decreasing the physical mobility of hexacyanoferrate.

The use of secondary ion mass spectrometry coupled with image analysis to identify and locate chemical elements in soil minerals: The example of phosphorus

AbstractThe mobility andbioavailability of elements in soils and sediments largely depends on their distribution on the diverse inorganic and organic constituents. This work addresses the example of phosphorus (P) associated to goethite and calcite, that is, to the major minerals involved in the retention of P in soils and sediments in calcareous environments. Synthetic goethite (FeOOH) and calcite (CaCO3) were reacted with P prior to being analysed by dynamic secondary ion mass spectrometry (SIMS). Powdery samples were embedded in resin, cut in thin sections, and imaged with a Cameca IMS 4F ion microscope used in scanning mode with a primary ion beam of caesium that produced negatively charged secondary ions (−) (Cameca, Cedex, France). Carbon, O, P, and calcium (Ca) were directly imaged at m/z 12, 16, 31, and 40, respectively, while Fe was imaged via the polyatomic ion FeO− ion at m/z 72. The SIMS data were treated by image analysis procedures. The visual comparison of images and the scatterplot method showed that P strongly interacted with goethite, probably following an adsorption process, and was thus evenly distributed at its surface. Conversely, P was not evenly distributed at the surface of calcite which rather suggests a precipitation process, and the scatterplot method confirmed a poor relationship between P and Ca. For the goethite‐calcite mixture, visual examination suggested that P occurred as clusters which were largely associated with calcite, whereas a statistical analysis of the various images showed that the distribution of P was largely related to that of goethite particles. This work confirms the potential contribution of iron oxides in the retention of P in calcareous environments and shows that coupling image analysis to sensitive analytical techniques such as SIMS is a powerful approach for providing quantitative information on the location of elements at low bulk concentrations.

High-Resolution Transmission Electron Microscopy Study of Newly Formed Sediments in the Atlantis II Deep, Red Sea

AbstractIron and silicon in various proportions are the major components of the newly formed hydrothermal sediments in the Atlantis II Deep, Red Sea. Iron-rich 2:1 phyllosilicates with morphologies varying from ribbons to plates represent clays in initial formation stage. Well-crystallized goethite particles contain domains of hundreds of nanometers in length with the rare presence of dislocations. Molar compositions show ratios of Si/Fe = 0.12 and Al/Fe = 0.05. Euhedral feroxyhyte with curled edges forms clusters with the goethite. The feroxyhyte has ratios of Si/Fe = 0.3 and are the major Si-associated iron oxides. Two nanometer-size phases showing short range periodity are common in the newly formed Atlantis II sediments: (1) hematite with traces of Si and (2) ferrihydrite with Si/Fe molar ratios varying between 0.17–0.89. The ferrihydrite forms large clusters. Hematite appears also as well-crystallized large crystals. Feroxyhyte probably forms at the transition zone between Red Sea Deep Water and the upper convective layer in the brine, whereas goethite and ferrihydrite form in the upper convective layer. The two forms of hematite represent two stages of recrystallization, which occur within the brine.

Modeling proton binding at the goethite (α-FeOOH)–water interface

The basic charging behaviours of goethite particles with different surfaces area (23, 37 and 85 m 2 g −1) in 0.003–2.0 M NaNO 3 were interpreted using surface complexation theory with the basic Stern model (BSM). The affinity of the goethite surface functional groups for protons was evaluated using the multisite complexation model (MUSIC) framework considering singly, doubly, and triply-coordinated surface oxygens with respect to underlying Fe(III) atoms. The affinity of these functional groups for protons was investigated first by using a calibration curve devised in Hiemstra et al. [J. Colloid Interface Science, 184 (1996) 680]. The calibration curve correlates the proton affinity constants of aqueous metal monomers to the undersaturation of the coordination environment of oxygens by considering the actual bond valences of FeO bonds in goethite, short hydroxyl bonds and hydrogen bonds. The results show that the predictions are sensitive to the range of short hydroxyl bonds/hydrogen bonds found in the literature. The singly- and one type of the triply coordinated sites are, however, most likely responsible for the basic charging behavior of goethite in the pH 2–11. The proton affinity constants of the singly- and triply coordinated sites were also optimized using titration data at different ionic strengths by co-optimizing values for electrolyte ion pairs and the capacitance of the Stern Layer. The optimal proton binding constants were in the range of the predicted values using the aforementioned calibration curve, although the modeling parameters are interdependent. A narrow range of C Stern and electrolyte ion pairs was chosen to model the charging behavior of goethite by considering, (i), the range of proton binding constants from the aforementioned calibration curve; and (ii), the success of the models to predict zeta potential measurements assuming that the shear plane coincides with the head of the diffuse layer. Modeling parameters were also produced with the ‘1p K approximation’ whereby the proton affinity constant of the singly- and of the triply-coordinated sites were set to the pH of zero charge and C Stern and the electrolyte ion binding constants were co-optimized. In both cases, the values of C Stern and of the electrolyte ion binding constants are slightly larger for the 23 and 37 m 2 g −1 goethites than for the 85 m 2 g −1. This indicates a larger proton uptake capacity of the 23 and 37 m 2 g −1 goethites, putatively resulting from the larger surface roughness at the termination of the particles.

エーテル変成ポリシロキサンコーティングによる水系塗料用酸化鉄粒子の分散性改善

Iron oxide pigments, such as hematite, goethite and magnetite particles are used as coloring material because of their suitable natural colors and chemical stability. Water-based paints with better dispersibility are strongly required in terms of environmental influence and for harmless handling recently.In this paper, we have investigated the coating by ether-modified poly siloxane onto iron oxide particles in order to improve the dispersibility in water-based paint. The coated iron oxide particles not only have better dispersibility but also good storage stability because of the larger negative charge on the modified siloxane coated particle surface in water-based paint.

Study of the mechano-chemical transformation of goethite to hematite by TEM and XRD

A study of the mechano-chemical transformation of goethite to hematite was carried out using transmission electron microscopy (TEM) and X-ray diffraction (XRD). Synthetic goethite was dry-ground in air for different times up to 104 h and characterized with the aim of understanding the mechanisms taking part in the transformation, the phases formed, and particle distribution, morphology and size. It was found that the transformation is topotactic, without the formation of intermediate phases, and takes place by fragmentation of crystals, creation of twins, dehydration of goethite particles, and formation of voids. The voids are arranged in almost parallel striations, and are associated with the loss of hydroxyl groups and formation of hematite in small domains of equiaxial crystallites. The hematite crystal size is about 10 nm at the initial stages and after prolonged periods of grinding remains constant at about 19 nm.

Benzenecarboxylate surface complexation at the goethite (α-FeOOH)/water interface: II. Linking IR spectroscopic observations to mechanistic surface complexation models for phthalate, trimellitate, and pyromellitate

A study combining information from infrared spectroscopy and adsorption experiments was carried out to investigate phthalate, trimellitate, and pyromellitate complexes at the goethite (α-FeOOH)/water interface. Infrared spectra showed evidence for inner-sphere complexes below pH 6 and outer-sphere complexes in the pH range 3 to 9. Normalized infrared peak areas were used as a semi-quantitative tool to devise diagrams showing the molecular level surface speciation as a function of pH. Surface complexation models that simultaneously predict these diagrams, the proton balance data and the ligand adsorption data were developed with surface complexation theory. Surface complexation modeling was carried out with a Charge Distribution Multisite Complexation Model (CD-MUSIC), assuming goethite particles with surfaces represented by the {110} plane (90% of total particle surface area) and by the {001} plane (10% of total particle surface area). Inner-sphere complexes were described as mononuclear chelates at the {001} plane, whereas outer-sphere complexes were described as binuclear complexes with singly coordinated sites on the {110} plane. The Three-Plane Model (TPM) was used to described surface electrostatics and to distribute the charges of the inner- and the outer-sphere complexes on different planes of adsorption.

Benzenecarboxylate Surface Complexation at the Goethite (α-FeOOH)/Water Interface: III. The Influence of Particle Surface Area and the Significance of Modeling Parameters

A surface complexation model describing the adsorption of three benzenecarboxylates (phthalate, trimellitate, and pyromellitate) on goethite (α-FeOOH) was calibrated on data using goethite particles of 37 and 43 m2/g surface area. The models predict potentiometric titration and batch adsorption data with the multisite complexation model coupled with the three-plane model to account for surface electrostatics. The modeling parameters were found to be similar to those calibrated on benzenecarboxylate adsorption data on goethite particles of 90 m2/g (Boily et al. Geochim. Cosmochim. Acta, in press). The significance of the benzenecarboxylate-dependent values of the modeling parameters is also discussed. The values of the capacitances of the inner- and outer-Helmholtz planes were shown to be important modeling parameters to model the benzenecarboxylate-dependent slopes of the adsorption edges. It was shown that the larger the charge of the ligand, the larger the capacitance of the outer-Helmholtz plane.

EFFECT OF AGING ON PARTICLE SIZE AND OXIDATION RATE IN THE FORMATION OF NEEDLE-LIKE GOETHITE PARTICLES BY AIR OXIDATION OF AQUEOUS FERROUS HYDROXIDE SUSPENSION

Needle-like goethite particles were synthesized by air oxidation of an alkaline suspension of ferrous hydroxide using a standard-type bubble column of 10cm in internal diameter and 64 cm in height at a constant temperature of 40°C. Specifically, the effect of aging step by N2 stream prior to the oxidation step was investigated on both the oxidation rate and the final particle size based on the major axis of needle-like goethite particle. The time dependence of the fractional oxidation of total ferrous species with incorporated aging step exceeded that in the absence of aging step. The velocity of N2 in the aging step had negligible influence on the time dependence of the fractional oxidation. For the aging period exceeding 30min, the mean particle size was almost independent of the aging period. The mean size could be correlated considerably well with the oxidation rate, that is, decreased with increasing oxidation rate with and without incorporated aging step.

Dissolution of Al-substituted goethites by an aerobic Pseudomonas mendocina var. bacteria

Goethite particles in soil environments often contain Al 3+ substituted for Fe 3+ in octahedrally coordinated sites. Al substitution has been shown to alter mineral stability and abiotic dissolution rates. This study focused on the effects of Al substitution (to 8.8 mol%) on synthetic goethite dissolution by an aerobic Pseudomonas mendocina var. bacteria. In contrast to dissimilatory iron reducing bacteria (DIRB), this bacteria is not capable of using Fe as a terminal electron acceptor for oxidative phosphorylation, and hence only requires μM concentrations of Fe for metabolism. Pure and substituted goethites were reacted with microorganisms in Fe-limited growth media wherein the only source of Fe was the solid phase, so that microbial populations could only grow by obtaining Fe through mineral dissolution. Because at least some Fe was taken up by the bacteria, we could not measure Fe release rates directly from dissolved Fe concentrations. Rather, we relied upon microbial growth measurements as indirect indicators of mineral dissolution. Increasing Al substitution resulted in particles with progressively decreasing mean particle length and aspect ratios, as well as fewer domains, as measured by atomic-force microscopy (AFM); but with increasing structural order as determined by XRD line widths. Experiments conducted in the dark at 22°C, exposed to the atmosphere, showed that maximum microbial population did not correlate with particle specific surface area, which is in contrast with previous studies using DIRB. Maximum microbial population increased a small amount with increasing Al content of the goethites, in contrast with several previous investigations of abiotic dissolution. Because dense biofilms formed, we were unable to use AFM to observe mineral dissolution features. AFM imaging suggested that more highly substituted goethites formed denser aggregates, and previous investigations have shown that aggregate structure is important for microbial attachment, which is prerequisite for dissolution. Hence, effects of Al substitution on aggregate structure is a focus of ongoing research.

Preparation of high acicular and uniform goethite particles by a modified-carbonate route

A procedure for the synthesis of high acicular and uniform goethite particles based on a modified-carbonate route is reported. It essentially consists of the oxidation–precipitation of iron sulfate solutions through a two-oxidation process, which involves the formation of primary particles and their subsequent growth. XRD, TEM, colour evolution and pH monitoring have been used to determine the mechanism responsible for the formation of goethite particles with well-controlled morphology. Single-phase goethite particles are formed from initial suspensions with OH/Fe equivalent ratios from 0.05 to 0.35, which determine the supersaturation level of the solution and consequently, the length of the particles. The best conditions to prepare uniform goethite particles of 250 nm in length and high axial ratio (8), adequate as high-density audio/video media precursors, have been established.

原料ゲータイト合成条件による針状γ‐Ｆｅ２Ｏ３粒子の形状・磁気特性の制御

Magnetic properties of acicular γ-Fe2O3 particles for magnetic recording media derived from goethite particles are regulated directly by controlling the morphology of goethite particles. The shape and magnetic properties of acicular γ-Fe2O3 by oxidizing weakly alkaline solution are examined by varying conditions: the initial Fe2+ concentration, the neutralization molar ratio in the seed reaction, and the partition of the rate of Fe2+ consumption either by the seed reaction or by the growth. Possible ranges of control are 200-300nm for the particle sizes, and 8 to 14 for the aspect ratio, while the S. D. of the aspect ratio between 2.5 to 5. Consequently, desirable acicular γ-Fe2O3 with a higher SQ and a lower SFD in the hysteresis curve can be synthesized.

Oxidation of chlorophenols with hydrogen peroxide in the presence of goethite

The use of goethite (α-FeOOH) and hydrogen peroxide was recently found that they could effectively oxidize organic compounds. The study was to investigate the effect of goethite particle size, goethite concentration, Fe 2+ and Fe 3+ on the 2-chlorophenol oxidation. Results indicated that 2-chlorophenol can be decomposed with hydrogen peroxide catalyzed by goethite and the oxidation rate increased with decreasing goethite particle size. 2-Chlorophenol degradation was almost retarded with 0.8 g/l of goethite because ferrous ions could not be produced at this condition. Addition of Fe 2+ and Fe 3+ can enhance the catalytic oxidation rate of 2-chlorophenol very efficiently. In conclusion, the main mechanism of goethite catalyzing hydrogen peroxide to oxidize 2-chlorophenol may be due to the catalysis of ferrous ions and goethite surface.

Self-stabilization of green rust (II) as a precursor of acicular goethite particles with highest possible aspect ratio

Acicular goethite particles were obtained by oxidation of weakly alkaline solutions containing varying amount of ferrous hydroxide. The change in pH during oxidation was analyzed in detail with special emphasis on the behavior of green rust (II), the metastable intermediate. Green rust (II) was stabilized by the buffering function of Fe 2+ in the solution. Coexistence of green rust (II) with goethite enables steady growth of goethite preferentially in the axial direction, resulting in an increase in the aspect ratio.

Mössbauer characterisation of the products resulting from hydrothermal treatments of nanosized goethite

Batches of poorly crystalline (GPC) and relatively well crystalline (GNL) goethite, α-FeOOH, powders have been suspended in a neutral aqueous medium and heated for three days in a pressure bomb at various temperatures between 100 and 300 °C. The parent and resulting products have been characterised by thermogravimetric analyses, X-ray diffraction, BET surface-area measurements, transmission electron microscopy and 57Fe Mössbauer spectroscopy. While the goethite particles of GNL are not affected by the treatments at up to 275 °C, those of GPC initially grow with increasing heating temperature up to ∼200 °C and subsequently become smaller with further increase of the temperature. Above 250 °C, GPC produces a mixture of hematite, α-Fe 2O 3, and maghemite, γ- Fe 2O 3. The presence of the latter phase is particularly obvious from the external-field Mössbauer spectrum. After being treated at 300 °C, both goethites have completely converted to hematite. The morphology of the parent goethite has no marked effect on the final hematite phase.

Effect of Phosphate on the Crystallization of Hematite, Goethite, and Lepidocrocite from Ferrihydrite

AbstractWe investigated the crystallization of ferrihydrite prepared by hydrolysis of Fe(NO3)3 solutions containing phosphate. Crystallization was studied at different pH (3–9), temperatures (298, 323, and 373 K), and initial P/Fe atomic ratios for periods to 730 d. Generally, crystallization was inhibited or only poorly crystallized lepidocrocite was formed at P/Fe > 2.5%. Phosphate favored the formation of hematite over goethite at all temperatures for most of the pH and P/Fe ranges investigated. This result is consistent with a model in which phosphate acts as a template for hematite formation, in analogy with other anions, such as oxalate. However, goethite was preferentially formed at alkaline pH and P/Fe > 1%, probably because high phosphate concentration resulted in a large increase in the negative charge of the ferrihydrite particles. This resulted in turn in less aggregation, a process that is known to precede dehydration to hematite. Phosphate greatly influenced the morphology of hematite and goethite. Hematite was often ellipsoidal or spindle-shaped. Twinned goethite crystals with a hematite core were formed at alkaline pH at P/Fe > 1%. Both hematite and goethite particles incorporated phosphate in an occluded form not desorbable by repeated alkali treatments.

Particle concentration effect and adsorption reversibility

The adsorption of zinc, copper and cadmium ions onto pure goethite particles in buffered aquatic systems was studied as a function of particle concentration ( C p). The dependence of the adsorption isotherms on the particle concentration is most obvious in the Zn–goethite system, less obvious in the Cu–goethite system, and undetectable in the Cd–goethite system. This result is in agreement with the observation that an increase in C p causes the biggest decrease in adsorption reversibility in the Zn–goethite system, a smaller decrease in reversibility in the Cu–goethite system and almost no changes in adsorption hysteresis in the Cd–goethite system. The results of experiments, designed to eliminate several typical sources of experimental artefact, agree with the prediction of the metastable-equilibrium adsorption theory (G. Pan, P.S. Liss, J. Colloid Interface Sci. 201 (1998) 71).

Reactions of copper and cadmium ions in aqueous solution with goethite, lepidocrocite, mackinawite, and pyrite

The uptake of Cu and Cd in aqueous solution by interaction with the surfaces of carefully synthesized finely sized particles of goethite, lepidocrocite, mackinawite, and pyrite was measured as a function of initial metal concentration in solution. The results show how reactions between metal ions in solution and mineral surfaces depend in a subtle way on the nature of the surfaces and, in certain cases, on the initial concentration of metal in solution. The uptake curves fall into two groups; type I in which the efficiency of uptake decreases with increasing concentration (Cu and Cd on goethite and lepidocrocite, Cd on pyrite), and type II in which it remains constant (Cu on mackinawite and pyrite, Cd on mackinawite). The total uptake is an order of magnitude greater for the latter group. X-ray absorption spectroscopies (XANES and EXAFS) were used to define the local environments of the metals taken up at the mineral surfaces. All examples showing the type I behavior yield information on local environments consistent with their being bound to the surfaces by an inner sphere complex formation mechanism. Thus, Cu on goethite appeared to form a Jahn-Teller distorted octahedral complex (four O atoms at 1.94 Aa; two O atoms at 2.41 Aa) but with evidence for interaction with two further Fe (or Cu) at 2.92 Aa. On lepidocrocite, the first coordination sphere was essentially identical to that on goethite but with a second Cu or Fe shell at 3.04 Aa and, for the highest Cu loadings, a third shell (2 Cu or Fe) at 3.67 Aa. The Cd on goethite showed best fits for sixfold coordination to O (at 2.26 Aa) but with evidence for a second shell of Fe atoms at 3.75 Aa. On lepidocrocite, the first shell was essentially the same as for goethite, but a second shell of Fe atoms appeared to occur at the shorter distance of 3.31 Aa. For Cd-loaded pyrite, best fits were given by a single shell of six O atoms at 2.27 to 2.28 Aa and with no evidence for a second shell of metal atoms. The systems exhibiting the type II behavior yielded spectra consistent with the formation of new phases on the surfaces, either by precipitation or replacement reactions. In the case of Cu interaction with mackinawite, a chalcopyrite phase appeared to form, whereas interaction with pyrite seemed to produce binary Cu sulfides--covellite at lower loadings and chalcocite at higher loadings. Cd interaction with mackinawite seemed to produce a CdS phase.

Complexation of Methylphosphonic Acid with the Surface of Goethite Particles in Aqueous Solution

Adsorption of methylphosphonic acid (MPA) onto goethite (α- FeOOH) was studied as a function of pH and the concentration of MPA in solution. In situ attenuated total reflectance-FTIR (ATR-FTIR) techniques were used to identify the type of surface complexes formed under each of the solution conditions used in the adsorption studies. Additionally, electrophoretic mobility measurements were performed in each of these systems. At low pH and high Γ, MPA was bound to the surface of goethite predominantly as a monodentate protonated species, while at high pH and low Γ the prevailing structure was that of a bridging bidentate complex. The change in denticity of the surface MPA under different solution conditions may explain the charge reversals shown in the electrophoretic mobility curves.