Goethite Particles Research Articles

An investigation of the mechanisms of goethite, hematite and magnetite-seeded Al(OH) 3 precipitation from synthetic Bayer liquor

The precipitation of Al(OH) 3 from synthetic Bayer liquor at 70 °C seeded with goethite, hematite and magnetite particles was investigated in order to gain insight into the nucleation and growth mechanisms in the presence of these materials. A combination of characterisation techniques was employed including conductivity analysis, particle size analysis, electron microscopy and in situ synchrotron X-ray diffraction. The magnetite seed was less active for promoting Al(OH) 3 precipitation than the goethite and hematite, based on a comparison of the induction time before the onset of measurable precipitation. For each seed material, the early stages of precipitation were characterised by relatively slow deposition of gibbsite on the seed particles. Precipitation then proceeded via a two-stage mechanism, where gibbsite and small amounts of bayerite and nordstrandite precipitated concurrently. The outcomes of this investigation have implications for the nucleation and growth of scale on mild steel process equipment, and are also relevant for alumina reversion which causes significant process losses through uncontrolled precipitation.

Fast Precipitation of Acicular Goethite from Ferric Hydroxide Gel under Moderate Temperature (30 and 70 °C)

The present study describes a simple and novel synthesis route for submicrometric acicular goethite (α-FeOOH) using high OH/Fe molar ratio (=5) and moderate temperature (30 and 70 °C). Two different alkaline sources (NaOH and Ca(OH)2) and two iron(III) sources (FeCl3·6H2O and Fe(NO3)3.9H2O) were investigated. FESEM, XRD, FTIR, N2 sorption isotherms, color evolution, and pH monitoring have been used to determine the formation mechanism, the particle size, specific surface area, and morphology of goethite particles. Three pH regions were determined during goethite formation, and each of them was qualitatively associated to (I) the formation of a ferric hydroxide gel, leading to acid conditions (pH 11) and fine sedimentable particles; and (III) the growth of goethite in alkaline conditions (11 < pH < 13.5). Both the temperature and the Fe(III) source have a significant effect on the particle size, specific surface area,...

Morphological Controls of Goethite Particle via Wet Synthesis from Ferrous Solution Applied for High-density Magnetic Recording Media

Morphological control of goethite particles by various operation conditions in a bench scale was devised in an attempt to improve magnetic properties of the end products. Reaction parameters were systematically varied and the detailed crystallographical analyses based on X-ray diffractometry and electron micrographs were employed as principal analytical tools.When ferrous sulfate and sodium hydroxide were used, precursors immediately before goethite were Fe(OH)2 or Green rust (II), at excess or deficiency of alkali, respectively. The superiority of goethite particles is mainly attributed to adequate lateral growth along (110) as compared to the growth rate in (010). Preferential lateral growth, in turn, was predominated by the concentration of FeOH+ complex ions. Green rust (II) was stabilized by the buffering function of Fe2+ 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.Since morphology of those magnetic materials is sustained from those of goethite, it is safe to conclude that proper choice of the starting ferrous source, extent of alkali excess and concentration of dissolved oxygen are the key factors for better goethite particles and, hence, better materials for magnetic recording.

Visible light scattering study at 470, 550, and 660 nm of components of mineral dust aerosol: Hematite and goethite

Iron oxides, usually in the form of hematite or goethite, comprise an important component of atmospheric mineral dust aerosol. Because these minerals are strong visible absorbers they play a critical role in determining the overall impact of dust aerosol on climate forcing. In this work, results from light scattering measurements from hematite and goethite dust aerosol are presented for three visible wavelengths, λ=470, 550, and 660 nm. We observe important systematic differences in the scattering between these different iron oxide samples, as well as significant wavelength dependence across the visible region of the spectrum. Aerosol size distributions are measured simultaneously with the light scattering, enabling a rigorous comparison between theoretical light scattering models and experimental data. Theoretical simulations of the scattering are carried out using both Mie and T-Matrix theories. Simulations are in reasonably good agreement with experimental data for hematite; thus, our data offer a useful check on tabulated optical constants for hematite. However, simulations show very poor agreement for goethite. The poor agreement in the goethite case is likely the result of particle shape effects related to the rod-like morphology of the goethite particles. This study demonstrates how particle mineralogy and morphology play an important role in dictating the optical properties of mineral dust aerosol, a major component of tropospheric dust.

Adsorption, Desorption, and Surface-Promoted Hydrolysis of Glucose-1-Phosphate in Aqueous Goethite (α-FeOOH) Suspensions

Adsorption, desorption, and precipitation reactions at environmental interfaces govern the fate of phosphorus in terrestrial and aquatic environments. Typically, a substantial part of the total pool of phosphorus consists of organophosphate, and in this study we have focused on the interactions between glucose-1-phosphate (G1P) and goethite (α-FeOOH) particles. The adsorption and surface-promoted hydrolysis reactions have been studied at room temperature as a function of pH, time, and total concentration of G1P by means of quantitative batch experiments in combination with infrared spectroscopy. A novel simultaneous infrared and potentiometric titration (SIPT) technique has also been used to study the rates and mechanisms of desorption of the surface complexes. The results have shown that G1P adsorption occurs over a wide pH interval and at pH values above the isoelectric point of goethite (IEP(goethite) = 9.4), indicating a comparatively strong interaction with the particle surfaces. As evidenced by IR spectroscopy, G1P formed pH-dependent surface complexes on goethite, and investigations of both adsorption and desorption processes were consistent with a model including three types of surface complexes. These complexes interact monodentately with surface Fe but differ in hydrogen bonding interactions via the auxiliary oxygens of the phosphate group. The apparent desorption rates were shown to be influenced by reaction pathways that include interconversion of surface species, which highlights the difficulty in determining the intrinsic desorption rates of individual surface complexes. Desorption results have also indicated that the molecular structures of surface complexes and the surface charge are two important determinants of G1P desorption rates. Finally, this study has shown that surface-promoted hydrolysis of G1P by goethite is base-catalyzed but that the extent of hydrolysis was small.

Negative Electrorheological Behavior in Suspensions of Inorganic Particles

An investigation is described on the electric-field-induced structures in colloidal dispersions. Both rheological determinations and direct microscopic observations are used with that aim. The starting point of this study is the so-called electrorheological (ER) effect, consisting of the mechanical reinforcing of a fluid or suspension due to formation of chains of molecules or particles after being polarized by the action of the field. One macroscopic manifestation of this phenomenon is the transformation of the fluid from a typically Newtonian behavior to a viscoelastic material, with finite yield stress and high elastic modulus. The systems investigated were suspensions of elongated goethite (β-FeOOH) particles in silicone oils with varying amounts of silica nanoparticles. The results showed the rather unusual behavior known as "negative ER effect", which can be best described by saying that the application of an electric field reduces the yield stress and the elastic modulus, that is, produces destruction of structures rather than their build up. The negative behavior is also found for suspensions of other inorganic powders, including hematite and quartz. On the contrary, the usual positive ER response is found for suspensions of cellulose and montmorillonite clay. The same happens if goethite suspensions are prepared in high volume fractions, high-viscosity fluids, or both. All of the results found are compatible with the so-called interfacial model of electrorheology: the reduction of the yield stress of goethite suspensions when the applied field is high enough is the consequence of particle migration toward the electrodes because of charge injection and subsequent electrophoresis. The migration leaves the gap between the electrodes devoid of particles and explains the decrease in yield stress. The addition of silica nanoparticles contributes to reduce the strength of this effect by hindering the charging and making it necessary to increase the field strength to observe the negative effect. The model appears to also be applicable to cellulose, although the positive response found for such particles is explained by their large size: larger diameters bring about larger attraction forces between particles, leading to a tendency to produce strong aggregates. This is likely to occur in suspensions of colloids which, because of their relatively high electrical conductivity, tend to acquire charge even in such nonpolar liquids as silicone oils.

The influence of platinum(IV) ions on the formation of iron oxides in a highly alkaline medium

The effect of the presence of platinum(IV) ions, in the form of Pt ( OH ) 6 2 - at a high pH, on the formation of iron oxides in a highly alkaline precipitation system was investigated using X-ray powder diffraction (XRD), 57Fe Mössbauer and FT-IR spectroscopies, field emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray spectroscopy (EDS). Monodispersed lath-like α-FeOOH (goethite) particles precipitated by hydrothermal treatment in a highly alkaline medium with the addition of tetramethylammonium hydroxide (TMAH) were used as reference material. In the presence of 1 or 5 mol% of platinum ions in the precipitation system the lath-like α-FeOOH particles were formed as a single phase after a short hydrothermal treatment (2 h). No significant change in the size and shape of these particles in comparison to the reference sample was observed. After 6 h of autoclaving the formation of platinum nanoparticles at the surface of α-FeOOH particles via reduction by TMAH and/or its decomposition products became visible. These nanoparticles acted as a catalyst for the reduction of Fe(III) ions into Fe(II) and gradual transformation of α-FeOOH into a mixed Fe(II)–Fe(III) oxide (Fe 3O 4, magnetite) by the dissolution–recrystallization mechanism. The presence of a higher concentration of platinum ions accelerates the process of α-FeOOH → Fe 3O 4 transformation with the appearance of α-Fe 2O 3 (hematite) particles as an intermediate product.

Liquid crystal phase behavior of sterically-stabilized goethite

The liquid crystalline phase behavior of sterically-stabilized goethite particles in toluene was studied using small-angle X-ray scattering. The results were compared with those from charged particles in water, with and without magnetic field: similarly rich phase behavior was found. Furthermore, the special magnetic properties were retained after coating the particles with amino-functionalized polyisobutylene chains. A remarkable difference between the aqueous and toluene samples is the latter's tendency to form gels. Smaller domains of the different liquid crystalline phases were observed and the columnar phase does not fully develop, furthermore a higher field is needed to align the full sample.

Interactions of chelating agents with Pb-goethite at the solid–liquid interface: Pb extraction and re-adsorption

The use of ethylenediaminetetraacetic acid (EDTA) for soil remediation is under concern due to its non-biodegradability and toxicity; thus, its biodegradable structural isomer, [S,S]-ethylenediamine disuccinate ([S,S]-EDDS), has been proposed as an emerging substitute. In this study, batch experiments were performed to quantify the Pb extraction from goethite by EDTA and EDDS, respectively, and attenuated total reflectance-Fourier transform infrared (ATR/FT-IR) spectroscopy was used to investigate the corresponding mechanisms at the solid–liquid interface at different pH and reaction times. The Pb extraction was pH-dependent for both chelating agents; mildly alkaline condition was favorable for EDDS, while mildly acidic condition for EDTA. The discrepancy between two structural isomers might be caused by their pH-dependent zwitterionic structures. The ATR/FT-IR results revealed that under acidic conditions, hydrogen-bonded carboxyl groups were present in both zwitterionic EDDS and EDTA. However, ring structure of zwitterionic EDDS formed with stable intramolecular hydrogen bond might limit the availability for EDDS to extract Pb from goethite. On the other hand, each protonated amine of zwitterionic EDTA could form hydrogen bonds with two neighbouring carboxyl groups, intensifying the negative charge of carboxyl groups and enhancing the Pb extraction efficiency. However, there was a higher amount of re-adsorption of PbEDTA than PbEDDS, because zwitterionic EDTA resulted in a greater Pb extraction and facilitated iron dissolution which significantly altered the goethite morphology, particle size, and surface area. These results suggested that, despite being structural isomers, EDDS and EDTA resulted in varying extents of Pb extraction and re-adsorption due to their different zwitterionic properties.

Uniaxial and biaxial liquid crystal phases in colloidal dispersions of board-like particles

Dispersions of board-like goethite (α-FeOOH) particles with short-range repulsive interaction form a versatile colloidal model system, showing a nematic, smectic A and columnar phase. In high magnetic fields a biaxial nematic phase is induced with the shortest dimension of the particles aligned along the field. Moreover, if particles have a shape almost exactly in between rod-like and plate-like they can spontaneously, without external magnetic field, form biaxial nematic and biaxial smectic A phases, which is in accordance with theoretical predictions. The macroscopic domains were oriented by a magnetic field and their structure was revealed by small-angle X-ray scattering. Our results suggest that biaxial phases can be readily obtained by a proper choice of the particle shape.

The heterogeneous photo-Fenton reaction using goethite as catalyst

In the present work the degradation of 2-chlorophenol (2-CP) used as model compound, applying the Heterogeneous photo-Fenton reaction, was studied. Small particles of goethite or iron oxyhydroxide were used as a source of iron. The influence of catalyst loading, radiation intensity and the molar ratio between hydrogen peroxide and contaminant were examined. Improvement by illumination is highly significant. During the progress of 2-CP degradation, the reaction shows an unusual acceleration. This autocatalytic comportment, with stronger tendencies at higher temperatures, implies a completely different behaviour from the one typically expected. The autocatalytic performance is successfully explained by the joint action of two factors: (i) the evolution of the available iron in the homogeneous phase during the course of the reaction and (ii) the autocatalytic contribution of some of the reaction intermediates in the iron cycle. The small iron concentration leaching into the solution is produced by two typical liquid medium - solid goethite surface dissolution processes. A reaction mechanism has been proposed and, in a first stage, parameters have been obtained for the dark reaction. In a second step, the complete data for the irradiated operation were obtained.

Analysis of phosphate adsorption onto ferrihydrite using the CD-MUSIC model

Ferrihydrite nanoparticles may dominate the ion binding properties of the natural oxide fraction present in soil and aquatic systems. A correct description of the adsorption properties of ferrihydrite nanoparticles may be useful for gaining a better insight into the adsorption processes in natural systems and at the same time will be essential for developing surface complexation models able to describe these processes. In the present study, phosphate speciation in ferrihydrite has been analyzed combining the available spectroscopic data and molecular information with modeling calculations. For this purpose, a new data set that analyzes the effect of pH and ionic strength on the phosphate adsorption onto ferrihydrite has been used. Description of the phosphate adsorption process onto ferrihydrite nanoparticles, for the entire pH and ionic strength range, has been made taking into account the presence of protonated and nonprotonated bidentate surface complexes. The presence of monodentate complexes, protonated and nonprotonated, was also analyzed, but no significant improvement in the description of the results was observed. The surface complexation constants obtained with the CD-MUSIC modeling calculations are comparable to the values found in the literature for phosphate surface complexes in goethite particles.

Anisotropic growth of multi-twinned goethite particles by oriented aggregation

Goethite (α-FeOOH) nanostructures with tunable sizes and shapes were prepared by aging ferrihydrite nanoparticles in aqueous media without the assistance of organic additives. Novel anisotropic assemblies of α-FeOOH nanocrystallites were characterized by high-resolution TEM. In particular, various stages of twinning mediated by oriented aggregation were identified on α-FeOOH particles for the first time. Oriented aggregation not only leads to one-dimensional (1D) assembly of nanoparticles, but results in two-dimensional (2D) side-by-side organization of twinned nanorods. The rod-like 1D and 2D particles show pseudoperiodical multi-twinning nanostructures along the <112> direction. The results from the current study shed new light on oriented aggregation, which directs extended defect structures as building blocks for self-assembling unique and useful nanocrystals.

Experimental Realization of Biaxial Liquid Crystal Phases in Colloidal Dispersions of Boardlike Particles

Biaxial nematic and biaxial smectic phases were found in a colloidal model system of goethite (alpha-FeOOH) particles with a simple boardlike shape and short-range repulsive interaction. The macroscopic domains were oriented by a magnetic field and their structure was revealed by small angle x-ray scattering. In accordance with theoretical predictions, biaxiality appears in a system with particles that have a shape almost exactly in between rodlike and platelike. Our results suggest that biaxial phases can be readily obtained by a proper choice of the particle shape.

Electric permittivity of concentrated suspensions of elongated goethite particles

This paper describes an investigation on the electric permittivity of concentrated suspensions of non-spherical particles, specifically prolate spheroids. It is first discussed how the determination of the frequency ( ω) dependence of the electric permittivity (a phenomenon traditionally known as LFDD or low-frequency dielectric dispersion) can provide ample information on the properties of the dispersed material (shape, size, state of aggregation, conductivity) and of its interface with the (typically aqueous) medium. The basic quantities are the strength and frequency dependence of the dipole moment induced by the applied field, and its dimensionless counterpart, the dipole coefficient, C ∗( ω). It is explicitly shown how the (complex) relative permittivity of the suspension, ε r ∗ ( ω ) , can be calculated from it. Two theoretical models on the polarizability of spheroidal colloidal particles will be used as theoretical starting point; one of them (Model I) explicitly considers two relaxations of the permittivity, each associated to one of the particle axes. The other (Model II) is a semi-analytical theory that yields an LFDD practically independent of the axial ratio of the particles. Both models are aimed to be used if the suspensions are dilute (low volume fraction of solids, ϕ ), and here they are generalized to concentrated systems by means of a previously published approximate evaluation of the permittivity of concentrated suspensions. Experiments are performed in the 1 kHz–1 MHz frequency range on suspensions of elongated goethite particles; the effects of ionic strength, pH, and volume fraction are investigated, and the two models are fitted to the data. In reality, taking into account that the particles are non-uniformly charged (a fact that contributes to their instability), two zeta potentials (roughly representing the lateral surface and the tip of the spheroid) are used as parameters. The results indicate that, when experimental conditions are optimal (high ionic strength and low zeta potential), the suspensions do indeed display two relaxations, that we ascribe to the long axis (and to flocs likely present in suspension) and to the short one. The permittivity increases with ionic strength, a result found with other systems, and compatible with a zeta potential that, on the average, decreases with ionic strength, an equally well known result, consequence of electric double layer compression. Another reasonable finding is the increase of estimated average dimensions and the decrease of electrokinetic potentials when the pH is close to the isoelectric point of goethite (around pH 9). The increase in volume fraction, finally, produces an overall increase in the permittivity, and the approximate model used for the evaluation of volume fraction variations can describe properly these effects, with basically constant zeta potentials and dimensions.

PH and temperature dependent facile precipitation of nano-goethite particles in Fe(NO 3) 3–NaOH–NH 3NH 2HSO 4–H 2O medium

A new synthesis route for producing nanosized crystallites of acicular goethite particles using ferric nitrate, hydrazine sulphate and sodium hydroxide is reported. The process steps essentially consist of a four-step procedure: (i) partial reduction of Fe(III) to Fe(II) due to the addition of hydrazine sulphate to ferric nitrate solution, (ii) formation of ferrihydrite primary particles, (iii) their transformation to goethite, and (iv) the growth of the goethite nuclei. X-ray diffraction, transmission electron microscopy and infrared spectroscopy data have been used to determine the phase formation under different pH and temperature conditions. Depending on the pH of precipitation ferrihydrite (pH 2–5), goethite (pH 7) or a mixture of goethite and magnetite (pH 9–12) was obtained when precipitation was carried out in the presence of hydrazine sulphate whereas in its absence under similar conditions only ferrihydrite was formed up to a pH of 9 and at pH 12 a mixture of ferrihydrite and goethite was observed. Addition of hydrazine sulphate reduced the pH formation of goethite. Precipitation was also carried out by maintaining temperature in the range of 300–353 K at a pH of 3. The results show that uniform goethite particles of 200–400 nm length with a high axial ratio of 10, can be obtained at a pH of 7 at room temperature and pure goethite can also be obtained at 353 K at a pH of 3.

Topochemical growth of textured polycrystalline barium hexaferrite from oriented antiferromagneticα-FeOOH nanorods

Nanorods of goethite, i.e. α-FeOOH, were mixed with BaCO3, dispersed in a polymer solution, and oriented under a 90 kOe magnetic fieldduring polymerization. The orientation arose principally from the interaction of themagnetic field with the anisotropic antiferromagnetism of the goethite particles. Theoriented antiferromagnetic particles act as seeds for the topochemical growth ofBaFe12O19 ferrite grains along the [0001] direction. The degree of grain orientation was determinedusing magnetic measurements and orientation distribution functions and pole figuresdetermined by electron backscatter diffraction analysis.

Nickel laterite Part 1 – microstructure and phase characterisations during reduction roasting and leaching

Detailed microstructure and phase characterisations of processed nickel laterite ore feed, reduced ore and leached ore have been carried out using scanning electron microscope, synchrotron X-ray powder diffraction and electron probe X-ray microanalysis as a part of study aimed to increase Ni recovery from the laterite ores. The majority of the nickel in the ore feed were found to be associated with fine grained goethite (Fe rich matrix of limonite composite) and serpentine particles. These phases were transformed to magnetite and olivine respectively upon reduction roasting. Nanosize metallic particles were also observed on the free surface of limonite composite particles following reduction roasting. Upon leaching, >90% of the nickel in the Fe rich matrix was leached out, while <50% was removed from the olivine and its composites. The characterisation results from this study were used to assist the analysis of thermodynamic and phase changes during reduction roasting and leaching described in Part 2 of the paper.

Nickel laterite Part 2 – thermodynamic analysis of phase transformations occurring during reduction roasting

Thermodynamic and phase transformation analyses of nickel laterite ores processed in industry have been carried out. The nickel in the laterite ores is principally associated with Fe rich goethite and serpentine particles. The thermodynamic analysis suggests that the nickel recovery from the Fe rich matrix is limited by equilibrium. The nickel recovery from the single phase serpentine/olivine appears to be higher for particles with Mg/Fe molar ratio <8. The nickel partitioning to the alloy phase is sensitive to the change of temperature and oxygen partial pressure both in the case of reduction roasting of Fe rich goethite and serpentine. It has also been shown in the current study that the optimum conditions for high nickel recovery from the Fe rich goethite and serpentine are different.

Solid-phase photocatalytic degradation of polyethylene–goethite composite film under UV-light irradiation

A novel photodegradable polyethylene–goethite (PE–goethite) composite film was prepared by embedding the goethite into the commercial polyethylene. The degradation of PE–goethite composite films was investigated under ultraviolet light irradiation. The photodegradation activity of the PE plastic was determined by monitoring its weight loss, scanning electron microscopic (SEM) analysis and FT-IR spectroscopy. The weight of PE–goethite (1 wt%) sample steadily decreased and led to the total 16% reduction in 300 h under UV-light intensity for 1 mW/cm 2. Through SEM observation there were some cavities around the goethite powder in the composite films, but there were few changes except some surface chalking phenomenon in pure PE film. The degradation rate could be controlled by changing the concentration of goethite particles in PE plastic. The degradation of composite plastic initiated on PE–goethite interface and then extended into polymer matrix induced by the diffusion of the reactive oxygen species generated on goethite particle surface. The photocatalytic degradation mechanism of the composite films was briefly discussed.