Showing papers on "Goethite published in 2014"
TL;DR: The first detailed study of the kinetics of the Fe(II)-accelerated transformation of ferrihydrite to goethite, via lepidocrocite, for a range of pH and Fe( II) concentrations is presented and insight is provided into the factors controlling the transformation rate and the processes responsible for transformation.
Abstract: Aqueous ferrous iron (Fe(II)) accelerates the transformation of ferrihydrite into secondary, more crystalline minerals however the factors controlling the rate and, indeed, the underlying mechanism of this transformation process remain unclear. Here, we present the first detailed study of the kinetics of the Fe(II)-accelerated transformation of ferrihydrite to goethite, via lepidocrocite, for a range of pH and Fe(II) concentrations and, from the results obtained, provide insight into the factors controlling the transformation rate and the processes responsible for transformation. A reaction scheme for the Fe(II)-accelerated secondary mineralization of ferrihydrite is developed in which an Fe(II) atom attaches to the ferrihydrite surface where it is immediately oxidized to Fe(III) with the resultant electron transferred, sequentially, to other iron oxyhydroxide Fe(III) atoms before release to solution as Fe(II). This freshly precipitated Fe(III) forms the nuclei for the formation of secondary minerals and also facilitates the ongoing uptake of Fe(II) from solution by creation of fresh surface sites. The concentration of solid-associated Fe(II) and the rate of transport of Fe(II) to the oxyhydroxide surface appear to determine which particular secondary minerals form and their rates of formation. Lepidocrocite growth is enhanced at lower solid-associated Fe(II) concentrations while conditions leading to more rapid uptake of Fe(II) from solution lead to higher goethite growth rates.
255 citations
TL;DR: The possible physicochemical properties of theGoethite surface contributing to the strong affinity of goethite to nutrients and contaminants in natural environment are reported and the suggested adsorption mechanism for these adsorbates was elucidated, which will help to understand the role ofgoethite in natural environments and provide some information about goethites as an absorbent.
161 citations
TL;DR: To understand the interplay of Fe/S cycling under alkaline conditions, thermodynamic geochemical modeling with bioreactor experiments using Shewanella oneidensis MR-1 were combined, finding that S.oneidensis can enzymatically reduce S0 but not goethite (α-FeOOH), and Fe(III) reduction may proceed via S0-mediated electron-shuttling pathways.
Abstract: Microbial reduction of ferric iron [Fe(III)] is an important biogeochemical process in anoxic aquifers. Depending on groundwater pH, dissimilatory metal-reducing bacteria can also respire alternative electron acceptors to survive, including elemental sulfur (S0). To understand the interplay of Fe/S cycling under alkaline conditions, we combined thermodynamic geochemical modeling with bioreactor experiments using Shewanella oneidensis MR-1. Under these conditions, S. oneidensis can enzymatically reduce S0 but not goethite (α-FeOOH). The HS– produced subsequently reduces goethite abiotically. Because of the prevalence of alkaline conditions in many aquifers, Fe(III) reduction may thus proceed via S0-mediated electron-shuttling pathways.
157 citations
TL;DR: A mass balance model is derived to quantify the extent of Fe atom exchange between goethite and aqueous Fe(II) that accounts for different Fe pool sizes and results from sequential chemical extractions indicate that (57)Fe accumulates in extracted Fe(III)Goethite components.
Abstract: Results from enriched 57Fe isotope tracer experiments have shown that atom exchange can occur between structural Fe in Fe(III) oxides and aqueous Fe(II) with no formation of secondary minerals or change in particle size or shape. Here we derive a mass balance model to quantify the extent of Fe atom exchange between goethite and aqueous Fe(II) that accounts for different Fe pool sizes. We use this model to reinterpret our previous work and to quantify the influence of particle size and pH on extent of goethite exchange with aqueous Fe(II). Consistent with our previous interpretation, substantial exchange of goethite occurred at pH 7.5 (≈ 90%) and we observed little effect of particle size between nanogoethite (average size of 81 × 11 nm; ≈ 110 m2/g) and microgoethite (average size of 590 × 42 nm; ≈ 40 m2/g). Despite ≈90% of the bulk goethite exchanging at pH 7.5, we found no change in mineral phase, average particle size, crystallinity, or reactivity after reaction with aqueous Fe(II). At a lower pH of 5.0...
151 citations
TL;DR: In this article, the authors investigated the effect of initial pH on the degradation of dibutyl phthalate (DBP), the formation and evolution of iron corrosion products, and the role of iron oxides on the further degradation of DBP in zero-valent iron (ZVI)-persulfate system.
128 citations
TL;DR: Weathering steel manufactured with high concentrations of copper (0.5",wt%), chromium ( 0.5,wt%), and nickel (2.4,wt%) was studied with the aim of furthering knowledge on corrosion product characterization and performance in marine environments as discussed by the authors.
109 citations
TL;DR: The role of reactive oxygen species, such as hydrogen peroxide, the hydroxyl radical and superoxide, towards the overall oxidation of Fe(II) was examined but found to have only a minor impact on Fe( II) oxidation when compared to the effect of heterogeneous oxidation.
97 citations
TL;DR: In this article, the desorbing agent is greatly dependent on the adsorbate used, and it is found that the metal ions are desorbed using acids like HCl, HNO 3 and H 2 SO 4 in most cases, except Cr(VI).
Abstract: Adsorption and desorption studies on different types of adsorbents, including natural materials such as teak tree bark powder, rice husk, natural bentonite, different algae like Ecklonia maxima, Escherichia coli, Ascophyllum nodasum, Rhizopus nigricans, Cladophora fascicularis, goethite and soils of three nuclear power plant and artificial materials such as Fe oxide-coated sand, goethite pretreated with phosphate, dithizonemodified sodium trititanate whisker, modified nanometre sized TiO 2 , Chromosorb 102 resins and poly(m-phenylenediamine) are summarized. The kinetics, thermodynamics, sorption/desorption mechanism of different metal ions on different adsorbents under different experimental conditions are discussed. It is found that desorbing agent is greatly dependent on the adsorbate used. All the metal ions are desorbed using acids like HCl, HNO 3 and H 2 SO 4 in most of the cases, except Cr(VI). EDTA can be used to remove Pb 2+ and Zn 2+ in addition to acids. Since Cr(VI) is present in anionic form; it can be eliminated from the loaded adsorbents using bases like NaOH, Na 2 CO 3 or NaHCO 3 .
95 citations
TL;DR: A geochronology of 147 grains of goethite cements extracted from ferruginous duricrusts (cangas) developed on banded iron-formations from the Quadrilatero Ferrifero region, Minas Gerais, Brazil, records a history of protracted mineral dissolution as discussed by the authors.
95 citations
TL;DR: Varying the Fe/S ratio revealed that surface polysulfide formation only becomes dominant when the remaining aqueous sulfide concentration is low, and it is proposed that these species play an overlooked role in the sulfur cycle.
Abstract: Polysulfides are often referred to as key reactants in the sulfur cycle, especially during the interaction of ferric (hydr)oxides and sulfide, forming ferrous-sulphide minerals. Despite their potential relevance, the extent of polysulfide formation and its relevance for product formation pathways remains enigmatic. We applied cryogenic X-ray Photoelectron Spectroscopy and wet chemical analysis to study sulfur oxidation products during the reaction of goethite and lepidocrocite with aqueous sulfide at different initial Fe/S molar ratios under anoxic conditions at neutral pH. The higher reactivity of lepidocrocite leads to faster and higher electron turnover compared to goethite. We were able to demonstrate for the first time the occurrence of surface-associated polysulfides being the main oxidation products in the presence of both minerals, with a predominance of disulfide (S2(2-)(surf)), and elemental sulfur. Concentrations of aqueous polysulfide species were negligible (<1%). With prior sulfide fixation by zinc acetate, the surface-associated polysulfides could be precipitated as zerovalent sulfur (S°), which was extracted by methanol thereafter. Of the generated S°, 20-34% were associated with S2(2-)(surf). Varying the Fe/S ratio revealed that surface polysulfide formation only becomes dominant when the remaining aqueous sulfide concentration is low (<0.03 mmol L(-1)). We hypothesize these novel surface sulfur species, particularly surface disulfide, to act as pyrite precursors. We further propose that these species play an overlooked role in the sulfur cycle.
89 citations
TL;DR: In this article, the authors used the three-isotope method to evaluate Fe isotope fractionation and the attainment of equilibrium by employing a multi-direction approach to equilibrium at 22 C via reaction of three Fe(II)aq solutions that had different initial 56 Fe/54 Fe ratios.
TL;DR: Radium and barium uptake onto ferrihydrite and goethite have been studied in the concentration range 1nM to 5mM and from pH 4 to 10, to develop a model to predict radium behavior in legacy uranium mining wastes as discussed by the authors.
TL;DR: A multi-method data set combining wet chemical and synchrotron-based X-ray diffraction (XRD) andX-ray absorption near-edge spectroscopy (XANES) methods to resolve the tight coupling of iron (Fe) and sulfur (S) geochemical changes in the top 2 m of tailings is reported.
TL;DR: Results indicated that Ca(2+) and phosphate have a great influence on the distribution of LEV in soils and waters, which will eventually affect its antibacterial activity in the environment.
TL;DR: A charge distribution surface complexation model was developed and could well predict the adsorption behavior of TC under a relatively wide range of pH, ionic strength and surface coverage, however, the model might overestimate the advertisersorption when TC surface coverage is higher than 1.42 μmol m(-2).
TL;DR: In this paper, an efficient adsorbents for arsenate removal was developed by modification of calcined eggshell with goethite, and the results of Visual MINTEQ equilibrium speciation modeling program was used for studying pH, ionic strength and interfering ions influences on arsenate adsorption.
TL;DR: In this paper, chemical and mineral transformations of a goethite ore were studied by dehydroxylation, reduction roasting in CO and CO2 gas mixtures, and magnetic separation.
TL;DR: In this article, the surface properties and phosphate adsorption of goethite, kaolinite, GKM and GKA were investigated, and the results indicated that GKA was a highly effective adsorbent for phosphate.
TL;DR: In this article, a geometric optimization of oleate on the stable and most exposed planes of hematite, magnetite, and goethite was carried out to determine the interaction energies for oleates-mineral surface.
TL;DR: In this article, the reductive capacity of the ZVIs was assessed by removal of Cr(VI) at ambient temperature in comparison with that of commercial iron powder (CIP).
TL;DR: X-ray absorption spectroscopy results suggested that U(VI) reduction was driven by the production of goethite under the conditions used in these studies, and this interpretation was supported by additional experimental evidence that demonstrated the (fast) reduction of U( VI) to U(V) by Fe(II) in the presence ofGoethite only.
Abstract: X-ray absorption spectroscopy has been used to study the reduction of adsorbed U(VI) during the Fe(II)-accelerated transformation of ferrihydrite to goethite. The fate of U(VI) was examined across a variety of pH values and Fe(II) concentrations, with results suggesting that, in all cases, it was reduced over the course of the Fe(III) phase transformation to a U(V) species incorporated in goethite. A positive correlation between U(VI) reduction and ferrihydrite transformation rate constants implies that U(VI) reduction was driven by the production of goethite under the conditions used in these studies. This interpretation was supported by additional experimental evidence that demonstrated the (fast) reduction of U(VI) to U(V) by Fe(II) in the presence of goethite only. Theoretical redox potential calculations clearly indicate that the reduction of U(VI) by Fe(II) in the presence of goethite is thermodynamically favorable. In contrast, reduction of U(VI) by Fe(II) in the presence of ferrihydrite is largely...
TL;DR: In this paper, a hexagonal bipyramid shape of octadecahedral α-Fe2O3 nanostructures was synthesized by adding F-anions in the solution.
Abstract: Driven by the demand for shape-controlled synthesis of α-Fe2O3 nanostructures and the understanding of their growth mechanism and shape-dependent properties, we report the synthesis of octadecahedral α-Fe2O3 nanocrystals with a hexagonal bipyramid shape by introducing F– anions in the solution. The hydrothermal growth process from hydrolysis of Fe3+ precursors involves three steps: the nucleation of akaganeite (β-FeOOH) nanorods, followed by the formation of goethite (α-FeOOH) crystals with acicular and twinned shapes, and a subsequent transformation into hematite (α-Fe2O3) nanoparticles. The phase transformation and growth of α-Fe2O3 particles from α-FeOOH follows dissolution of goethite and reprecipitation as hematite process. The initial nucleation of α-Fe2O3 particles was found to form epitaxially on goethite {001} surfaces due to a perfect lattice match between goethite {001} surface and hematite {001} planes. The structural relationship between goethite and hematite is G(020)//H(030) with G[100]//H[...
TL;DR: It was demonstrated that colloidal iron oxyhydroxide instead of soluble ferric iron played an important role in voltage production through maintaining high-concentration ferrous iron in pore water of sediments as electron shuttle and for chemical oxidation on the anode.
TL;DR: The decrease in pH of the reaction mixture after 48h reaction revealed that acidic products might be formed during degradation of PCB28, and the rate of H2O2 decomposition increased at higher pH and goethite concentration, and decreased at lower H2 O2 concentration.
TL;DR: The antimonite can be adsorbed and oxidized on goethite irradiated with light, which will greatly reduce its environmental risk.
TL;DR: In this article, the authors reported on the X-ray absorption analysis of samples of mineral dust emitted from or transported to Western Africa and found that iron oxides account, by mass, for 38% to 72% of the total elemental iron.
Abstract: This paper reports on the X-ray absorption analysis of samples of mineral dust emitted from or transported to Western Africa. We found that iron oxides account, by mass, for 38% to 72% of the total elemental iron. They are composed of minerals in the Fe(III) oxidation state: goethite (FeO·OH) and hematite (Fe2O3). The apparent fraction of iron oxide attributed to goethite is higher than hematite regardless of the source region from which the dust originated. The goethite percent content of iron oxides is in the range 52–78% (by mass), the highest values being measured for dust originating in the Sahel. The limited number of samples analyzed and the sample-to-sample variability prevent us from concluding firmly on the regional variability of the goethite-to-hematite ratio. Based on the experimental data on mineralogical composition and on concurrent measurements of the number size distribution, the optical properties of mineral dust have been calculated in a Mie approximation for homogeneous spherical particles. At 550 nm, the single-scattering albedo ω0 ranges between 0.89 and 0.93, the asymmetry factor g ranges between 0.76 and 0.8 and the mass extinction efficiency kext varies between 0.5 and 1.1 m2 g−1; these values are all in the range of those from independent direct measurements. Neglecting the partitioning between hematite and goethite and the assimilation of iron oxides by hematite, as it is often done with models, lowers the single-scattering albedo and increases the asymmetry factor in the UV-visible spectral region below 550 nm. The mass extinction efficiency is insensitive to the nature of the iron oxides but rather responds to variations in the number size distribution. The mineralogy of iron oxides should therefore be taken into account when assessing the effect of mineral dust on climate and atmospheric chemistry, in particular via interactions involving photolysis.
TL;DR: In this paper, the authors report the results of long-term experiments aimed at quantifying the maximum phosphorus adsorption capacity (MPAC) and its determinant mineralogical variables in Brazilian soils and at assessing the effect of no-tillage (NT) in mitigating the phosphorus adorption of soils.
Abstract: The low phosphorus availability in tropical and subtropical soils, normally related to adsorption of phosphate to the minerals surfaces, can be attenuated when organic matter (OM) accumulates in the soils. Herein, we report the results of long-term experiments (18-32 years) aimed at quantifying the maximum phosphorus adsorption capacity (MPAC) and its determinant mineralogical variables in Brazilian soils and at assessing the effect of no-tillage (NT) in mitigating the phosphorus adsorption of soils. The MPAC of soils ranged from 297 to 4,561 mg kg -1 in the 0.00-0.10 m layer and from 285 to 4,961 mg kg -1 in the 0.10-0.20 m layer. The MPAC was correlated with the concentrations of iron oxides, goethite and ferrihydrite, gibbsite/(gibbsite+kaolinite) ratio and the specific surface area. The OM increased in the 0.00-0.10 m layer of NT soils, which was not reflected on the decrease of MPAC for the no-tillage soils.
TL;DR: In this paper, the authors investigated the exchange of Hg(II) between dissolved species (inorganically complexed or cysteine-, EDTA-, or NOM-bound) and solid-bound Hg (II) (carboxyl-/thiol-resin or goethite) over 30 days under constant conditions (pH, Hg and ligand concentrations).
Abstract: The mobility and bioavailability of toxic Hg(II) in the environment strongly depends on its interactions with natural organic matter (NOM) and mineral surfaces. Using an enriched stable isotope approach, we investigated the exchange of Hg(II) between dissolved species (inorganically complexed or cysteine-, EDTA-, or NOM-bound) and solid-bound Hg(II) (carboxyl-/thiol-resin or goethite) over 30 days under constant conditions (pH, Hg and ligand concentrations). The Hg(II)-exchange was initially fast, followed by a slower phase, and depended on the properties of the dissolved ligands and sorbents. The results were described by a kinetic model allowing the simultaneous determination of adsorption and desorption rate coefficients. The time scales required to reach equilibrium with the carboxyl-resin varied greatly from 1.2 days for Hg(OH)2 to 16 days for Hg(II)-cysteine complexes and approximately 250 days for EDTA-bound Hg(II). Other experiments could not be described by an equilibrium model, suggesting that a significant fraction of total-bound Hg was present in a non-exchangeable form (thiol-resin and NOM: 53-58%; goethite: 22-29%). Based on the slow and incomplete exchange of Hg(II) described in this study, we suggest that kinetic effects must be considered to a greater extent in the assessment of the fate of Hg in the environment and the design of experimental studies, for example, for stability constant determination or metal isotope fractionation during sorption.
TL;DR: In this paper, the authors examined a former uranium mine where groundwater leaving the site enters a stream with chemically dramatic effects resulting in a fundamental change in the way contaminant metals are transported to the surface environment.
Abstract: Environmental context Legacy contamination from mining operations is a serious and complex environmental problem. We examine a former uranium mine where groundwater leaving the site enters a stream with chemically dramatic effects resulting in a fundamental change in the way contaminant metals are transported to the surface environment. The results are important for our understanding of how these contaminants are dispersed, and how they could interact with the biosphere. Abstract In this study of iron- and silica-bearing nanoparticle and colloid aggregates in slightly acidic mine drainage, we combined bulk scale geochemistry techniques with detailed nanoscale analyses using high-resolution transmission electron microscopy (HR-TEM) to demonstrate the complexity of iron oxide formation and transformation at a steep redox gradient (groundwater outflow into a stream), and the resulting role in metal(loid) uptake. We also identified pseudohexagonal nanosheets of Zn-bearing green rust in outflowing groundwater using HR-TEM. This is only the second study where green rust was identified in groundwater, and the second to examine naturally occurring green rust with analytical TEM. In aerated downstream waters, we found aggregates of poorly crystalline iron oxide particles (20–200nm in diameter). Inductively coupled plasma–mass spectrometry (ICP-MS) analysis of water fractions shows that most elements such as Ni and Zn were found almost exclusively in the dissolved–nanoparticulate (<0.1μm) fraction, whereas Cu and As were primarily associated with suspended particles. In the underlying sediments composed of deposited particles, goethite nanoneedles formed on the ferrihydrite surfaces of larger aggregated particles (100–1000nm), resulting in more reactive surface area for metal(loid) uptake. Sequential extraction of sediments showed that many metal(loid)s, particularly As and Zn, were associated with iron oxides identified as ferrihydrite, goethite and possibly schwertmannite. Amorphous silica co-precipitation with iron oxides was prevalent at all sampling sites, but its effect on metal(loid) sorption is unknown. Fine-grained iron oxide sediments are easily remobilised during turbulent flow events, adding to the mobility of the associated metals.
TL;DR: In this article, the authors examined the anaerobic reduction of synthesized jarosite by Shewanella oneidensis strain MR-1, a typical facultative bacteria, and found that the release of ferrous and ferric ion, as well as sulfate and potassium, in the inoculated experimental group lasting 80 days is much higher than that in abiotic control groups.