Showing papers on "Goethite published in 2000"

Remediation of Cr(VI) and Pb(II) aqueous solutions using supported, nanoscale zero-valent iron

Abstract: Borohydride reduction of an aqueous iron salt in the presence of a support material gives supported zero-valent iron nanoparticles that are 10−30 nm in diameter. The material is stable in air once it has dried and contains 22.6% iron by weight. The supported zero-valent iron nanoparticles (“Ferragels”) rapidly separate and immobilize Cr(VI) and Pb(II) from aqueous solution, reducing the chromium to Cr(III) and the Pb to Pb(0) while oxidizing the Fe to goethite (α-FeOOH). The kinetics of the reduction reactions are complex and include an adsorption phase. About 10% of the iron in the material appears to be located at active surface sites. Once these sites have been saturated, the reduction process continues but at a much lower rate, which is likely limited by mass transfer. Rates of remediation of Cr(VI) and Pb(II) are up to 30 times higher for Ferragels than for iron filings or iron powder on a (Fe) molar basis. Over 2 months, reduction of Cr(VI) was 4.8 times greater for Ferragels than for an equal weigh...

Dechlorination of Carbon Tetrachloride by Fe(II) Associated with Goethite

Abstract: Carbon tetrachloride (CT) was dechlorinated to chloroform (CF) under anoxic conditions by Fe(II) that was sorbed to the surface of goethite (α-FeOOH). No reaction occurred when Fe(II) was present and goethite was absent. Several abiotic experiments were conducted with goethite at 30 °C in which the total amount of Fe(II) in the system, the amount of sorbed Fe(II), the density of sorbed Fe(II), and the pH were varied. Regeneration of sorbed Fe(II) occurred when dissolved Fe2+ was available and maintained pseudo-first-order conditions with respect to CT. Analysis of the rates of CT loss for experiments with sorbed-Fe(II) regeneration showed the rate-determining-step to be first order with respect to CT, second order with respect to the volumetric concentration of sorbed Fe(II) (i.e., mmol sorbed Fe(II) L-1 suspension), and zero order with respect to H+ for pH between 4.2 and 7.3. The absolute rate constant for the reaction was determined to be 42 ± 5 M-2 s-1. Normalization of the observed rate constants to ...

Vibrational Spectroscopy Study of Selenate and Sulfate Adsorption Mechanisms on Fe and Al (Hydr)oxide Surfaces.

Abstract: The coordination and speciation of selenate (SeO(4)) and sulfate (SO(4)) on goethite and Al oxide were studied using Raman and ATR-FTIR spectroscopy. Raman spectra were collected from pastes of suspensions containing 4 mM SeO(4) or SO(4). For SO(4), complementary data were collected by ATR-FTIR spectroscopy in goethite systems with 1 mM SO(4) and in Al oxide systems with 4 mM SO(4). The combined data set of Raman and ATR-FTIR spectra indicate that both inner- and outer-sphere surface complexes of SeO(4) and SO(4) occur on these metal (hydr)oxide surfaces. These spectral data show that SeO(4) and SO(4) have a similar complexation behavior on the same adsorbent. On goethite, these form predominantly monodentate inner-sphere surface complexes at pH 6 these anions exist predominantly as outer-sphere surface complexes. On Al oxide, in contrast, these anions exist predominantly as outer-sphere surface complexes, but a small fraction is also present as an inner-sphere complex at pH <6. A comparison of the spectral intensities of these anions on goethite and Al oxide shows that complexation of these anions with Al oxide is weaker than with Fe oxide. Copyright 2000 Academic Press.

Uranium Uptake from Aqueous Solution by Interaction with Goethite, Lepidocrocite, Muscovite, and Mackinawite: An X-ray Absorption Spectroscopy Study

Abstract: The retention of radionuclides by interaction with mineral phases has significant consequences for the planning of their short- and long-term disposal to geological systems. An understanding of binding mechanisms is important in determining the ultimate fate of radionuclides following release into natural systems and will give increased confidence in predictive models. X-ray absorption spectroscopy (XAS) has been used to study the local environment of uranium taken up from aqueous solution by the surfaces of goethite, lepidocrocite, muscovite, and mackinawite. On both iron hydroxides uranium uptake occurs by surface complexation and ceases when the surface is saturated. The muscovite surface does not become saturated and uptake increases linearly suggesting formation of a uranium phase on the surface. Uranium uptake on mackinawite also suggests a replacement or precipitation process. XAS indicates that bidentate inner-sphere surface complexes are formed on the iron hydroxides by coordination of two surfac...

Effectiveness of phosphate and hydroxide for desorption of arsenic and selenium species from iron oxides.

Abstract: Phosphate and OH- are often used for the extraction of As and Se from soils, either as single extractants or as part of a sequential extraction scheme. However, the recovery of As and Se species and the integrity of the resulting solution speciation merit investigation. In this study the relative effectiveness of PO 4 at 0.1 and 0.5 M and pH values of 3 and 6.7 and 0.1 M OH to extract As(III), As(V), dimethylarsinic acid (DMA), monomethylarsonic acid (MMA), p-arsanilic acid (p-ASA), roxarsone (ROX), Se(IV) and Se(VI) sorbed to goethite and an amorphous Fe oxide were compared, and the speciation in the resulting extract was determined. The extent to which 0.1 M PO 4 added to 0.25 M NH 2 OH.HCl or 0.175 M Na oxalate/ 0.1 M oxalic acid prevents readsorption of As(V) or Se(IV) to goethite during the dissolution of an amorphous Fe oxide was also assessed. Hydroxide was the most effective extractant for desorption of all species except As(III) from both oxide surfaces. Arsenite was extracted most efficiently by 0.5 M PO 4 at low pH; however, amorphous Fe oxide exhibited a strong affinity for As(III) with a maximum of 18% of As(III) extracted by 0.5 M PO 4 at pH 2.8. Partial oxidation of As(III) to As(V) occurred in all extractions where an Fe oxide solid phase was present, but only in the hydroxide extract in the absence of a Fe solid phase. Addition of 0.1 M PO 4 to extractants used for the dissolution of the amorphous Fe oxide prevented the readsorption of As(V) and Se(IV) to goethite.

Changes in Soil Mineralogy and Texture Caused by Slash-and-Burn Fires in Sumatra, Indonesia

Abstract: We investigated the effect of fire intensity from slash-and-burn agriculture on the mineralogy of Oxisols in the Sepunggur area, Jambi Province, Sumatra, Indonesia, in both field and laboratory experiments. Samples were collected from two depths (0-5 and 5-15 cm) at locations exposed to 100,300,600, and >600°C surface temperatures during the burns. Soils under forest and slashed vegetation were collected as controls. The pre-burn soil mineralogy was dominated by kaolinite, gibbsite, anatase, and goethite. Changes in soil properties with burning were most pronounced in the 0- to 5-cm layer. Burning the topsoil led to coarser textures, especially at temperatures exceeding 600°C. Heat reduced the gibbsite and kaolinite concentrations and converted goethite into ultra-fine maghemite, thus increasing the magnetic susceptibility of the samples. The conversion of goethite did not take place until water in the samples had vaporized. Addition of organic matter to soil with a low organic C content before heating increased the magnetic susceptibility, indicating that organic matter was necessary (and limiting) for the complete conversion of goethite. Coarse-grained magnetite particles were present prior to and after the burning and, therefore, were not pyrogenic. Magnetic susceptibility measurements were highly discriminatory among heat treatments, whereas x-ray diffraction (XRD) was much less sensitive to fire-induced changes in mineralogy. Our research showed that severe burning had drastic effects on soil mineralogy, but changes should also be expected at lower fire intensities. Further research is needed to determine how important these changes in soil mineralogy are for nutrient availability in the growing season after the burn.

Electron flow in an iron‐rich acidic sediment—evidence for an acidity‐driven iron cycle

Abstract: The anoxic sediment of an acidic (pH ∼3) iron- and sulfate-rich lake and its pore water was studied with respect to the turnover rates of solid and dissolved iron and sulfur species High sedimentation rates of iron (570 g m−2 a−1) lead to an enrichment of the upper (0–5 cm) acidic sediment zone (pH < 4) with schwertmannite (Fe8O8(OH)x(SO4)y (∼ 350 g kg−1) Microbial iron-reduction rates measured by closed vessel incubation technique were highest close to the sediment-water interface (250 nmol cm−3 d−1), sulfate reduction measured by the 35S-tracer technique was not detectable in this zone The absence of sulfide allowed complete reoxidation of dissolved Fe(II) diffusing into oxic parts of the lake water Thus, an iron cycle is established where acidity generation through this process (10–47 mol m−2 a−1) balanced the alkalinity gain through microbial iron reduction in this zone (065–40 mol m−2 a−1) Predominance of iron over sulfate reduction under acidic conditions is further stabilized by the transformation of schwertmannite to goethite at a depth of 3–5 cm, which releases acidity at a rate of 35 mol m−2 a−1 Below, pore-water pH increased to values between 5 and 6, sulfate reduction occurred with a maximum rate of 14 nmol cm−3 d−1), sulfate reduction measured by the 35S-tracer technique was at 9 cm depth Release of Fe(II) and a short turnover time of reduced sulfur relative to the sediment age implies that most of the sulfide formed seemed to be recycled to sulfate at this depth, presumably coupled to the reduction of iron Consequently, net alkalinity is generated at low rates only (012 mol m−2 a−1)

Competition of Cd, Cu, and Pb Adsorption on Goethite

Abstract: Competition of copper, lead, and cadmium adsorption on goethite was studied and found to be dependent on metal ion and oxide surface characteristics. In adsorption edges, ionic strength effects suggested copper, lead, and cadmium are specifically adsorbed on goethite. Metal capacity on the goethite surface was found to increase with metal electronegativity: Cu > Pb > Cd. On the other hand, the equilibrium constant for lead was greater than that of copper, which is in agreement with their hydrated radii (Pb < Cu < Cd). Modeling revealed that the single-site Langmuir isotherm described the Cu-Cd and Pb-Cd adsorption and competition results within the error of the model. Furthermore, although the model provided a good fit for Pb and Cd data in the Pb-Cu and Pb-Cu-Cd systems, it underpredicted copper adsorption. The difference in site densities between copper and lead revealed a set of sites not available for competition. Using this approach where copper affinity is equivalent for both sites, the model provid...

Rates of Microbially Mediated Arsenate Reduction and Solubilization

Abstract: Reduction of arsenate [As(V)] to arsenite[As(III)] influences the mobility and toxicity of arsenic (As), yet the mechanisms controlling the rate of reduction in soils and natural waters are poorly understood. The goal of this study was to determine processes affecting reduction rates of both aqueous and sorbed phase As(V). Reduction experiments were conducted anaerobically in serum bottles with a range of glucose and As(V) concentrations. Serum bottles were inoculated with microorganisms extracted directly from an agricultural soil having naturally elevated concentrations of As (unenriched population), or with a pure culture isolate obtained from the same soil after enrichment for As(V) reduction. At As(V) concentrations ranging from 6 to 600 μM, the rate of As(V) reduction by the soil isolate was first order with respect to both As(V) concentration and microbial biomass. Reduction rates of As(V) with the soil isolate were 2 toll) fold greater than in the unenriched population, suggesting As(V) reducers represented only a subset of the unenriched population. Compiled data indicated that the pure culture isolate was fermenting glucose, and potentially reducing As(V) as a detoxification mechanism. In a parallel study, reduction rates of As(V) with the unenriched population were evaluated in the presence of goethite or ferrihydrite. When redox potential decreased from 500 to near 0 mV, aqueous As concentrations decreased by approximately 30% in a goethite suspension with a high As surface coverage, yet increased by seven fold in a goethite suspension with a low As surface coverage. In a ferrihydrite suspension, aqueous As concentrations during reduction increased approximately 100 fold faster than in a goethite suspension at similar initial aqueous As(V) concentrations, corresponding to differences in Fe oxide surface areas and reductive dissolution rates. The results indicate that rates of As mobilization during reduction in soils are highly dependent on oxide surface area and As surface coverage.

Zinc Immobilization and Magnetite Formation via Ferric Oxide Reduction by Shewanella putrefaciens 200

Abstract: Long-term batch experiments in an artificial groundwater medium indicated that microbial reduction of synthetic, high-surface-area goethite and lepidocrocite by Shewanella putrefaciens 200 can act to immobilize surface-associated zinc into a new mineral phase that is not soluble in 0.5 M HCl. While Zn was incorporated in siderite grains in experiments with goethite, additional Zn immobilization may result from incorporation into as yet unidentified biogenic minerals or into a more crystalline goethite. Experiments with an oxide mixture primarily composed of lepidocrocite resulted in the production of magnetite, biphasic im mobilization of Zn, and an enhanced overall degree of Zn immobilization. When NO3- was present as an alternate electron acceptor, microbial production of Fe(II) was inhibited, and the degree of Zn immobilization was subsequently reduced. These data indicate that (i) biologically induced mineralization can play a key role in the cycling of trace elements in natural systems, (ii) the natu...

Reductive Dissolution of Ferric Iron Minerals by Acidiphilium SJH

Abstract: The acidophilic heterotrophic eubacterium Acidiphilium SJH was shown to catalyze the reductive dissolution of a wide range of ferric iron?containing minerals (akageneite, goethite, jarosite, natrojarosite, and amorphous ferric hydroxide) and of the mixed ferrous/ferric mineral magnetite The specific rates of dissolution varied with the structural stabilities of the minerals, such that amorphous ferric hydroxide was the most rapid and jarosite and akageneite were the slowest of the minerals tested The reductive dissolution of both amorphous ferric hydroxide and magnetite was faster in pH 20 than in higher pH (28?30) cultures, even though Acidiphilium SJH has a pH optimum close to pH 3 Contact between bacteria and ferric mineral was not necessary for reductive dissolution to occur Adding EDTA or diethylenetriamine pentaacetic acid to bacterial cultures accelerated the solubilization of goethite and amorphous ferric hydroxide Although cell-free spent media and heat-killed Acidiphilium SJH also appear

Electrolyte Anion Affinity and Its Effect on Oxyanion Adsorption on Goethite.

Abstract: The influence of various types of background electrolytes (NaCl, NaNO3, and NaClO4) on the proton adsorption and on the adsorption of sulfate and phosphate on goethite have been studied. Below the PZC the proton adsorption on goethite decreases in the order Cl>NO3>ClO4. The decreasing proton adsorption affects the adsorption of oxyanions on goethite. Anion adsorption of strongly binding polyvalent anions is lower in the studied electrolytes in the order Cl

Effects of copper on the activity and kinetics of free and immobilized acid phosphatase

Abstract: Heavy metal pollution presents a major hazard to the soil environment. Studies have shown that the activities of a variety of soil enzymes are inhibited by heavy metals. However, little information is available concerning the effect of heavy metals on the activity of enzymes immobilized by different soil constituents. The main objective of this work was to investigate the effects of copper on the activity and kinetic properties of acid phosphatase both free and immobilized on two variable-charge soil clays and the minerals kaolin, goethite and manganese oxide. The effect of different forms of copper on enzyme activity was also examined. In the presence of copper chloride, the activity of free and immobilized enzymes was inhibited at copper concentrations of 0.005‐0.8 mM at pH 5.0 and inhibition increased at pH 6.0. The inhibitory effect of copper chloride was greater on the enzymes bound by the two soil clays and kaolin than those by goethite and MnO2. Addition of copper chloride decreased both the Km values and the Vmax/Km ratios of free and all forms of immobilized enzymes, and showed mixed type inhibition kinetics. Comparing the effect of different forms of Cu, the residual activities of free enzyme and soil clay‐enzyme and kaolin‐enzyme complexes were higher when copper citrate was used than with copper chloride. The reverse was true for the enzymes immobilized on goethite and MnO2. These results indicate that the inhibition by Cu of enzymes immobilized on soil components are influenced by the properties of the adsorbent and the form of Cu, as well as pH. q 2000 Elsevier Science Ltd. All rights reserved.

Adsorption and fractionation of a muck fulvic acid on kaolinite and goethite at pH 3.7,6, and 8

Abstract: Molecular weight (MW) of humic materials is a key factor controlling proton and metal binding and organic pollutant partitioning. Several studies have suggested preferential adsorption of higher MW, more aromatic moieties to mineral surfaces; quantification of such processes is fundamental to develo

The Effect of Al on Fe Oxides. XIX. Formation of Al-Substituted Hematite from Ferrihydrite at 25°C and pH 4 to 7

Abstract: Iron oxides in surface environments generally form at temperatures of 25 ± 10°C, but synthesis experiments are usually done at higher temperatures to increase the rate of crystallization. To more closely simulate natural environments, the transformation of 2-line ferrihydrite to hematite and goethite at 25°C in the presence of different Al concentrations and at pH values from 4 to 7 was studied in a long-term (16–20 y) experiment. Aluminum affects the hydrolysis and charging behavior of 2-line ferrihydrite and retards crystallization. Al also promotes the formation of hematite over goethite and leads to multidomainic discoidal and framboidal crystals instead of rhombohedral crystals. The strong hematite-promoting effect of Al appears to be the result of a lower solubility of the Al-containing ferrihydrite precursor relative to pure ferrihydrite. Hematite incorporates Al into its structure, as is shown by a decrease in the a and c-cell lengths and a decrease in magnetic hyperfine fields (Mossbauer spectroscopy). With hematite formed at low-temperature, these decreases were, however, smaller for the cell length and greater for the magnetic field than for hematite produced at higher temperatures. Both phenomena are removed by heating the hematite at 200°C. They are attributed to structural OH and/or structural defects. The relative content of Al in the structure is lower for hematite formed at 25°C than for hematites synthesized at higher temperatures (80 and 500°C). The maximum possible substitution of one sixth of the Fe positions was not achieved, similar to soil hematites. These results show that properties of widely distributed soil Al-containing hematites can reflect formation environment.

Identifying goethite and hematite from rock magnetic measurements of soils and sediments

Abstract: We describe a sequence of experiments involving the acquisition of isothermal remanent magnetization (IRM) in high (>2 T) fields, followed by orthogonal demagnetization and the cooling and heating of remanent magnetization (Mr) over the temperature range −196°C to +680°C. The main aim of these experiments is to improve the basis for identifying the imperfect antiferromagnetic minerals contributing to the magnetic properties of natural soil and sediment samples, which often contain complex mineral mixtures. The procedures developed are first applied to a series of ore and synthetic samples of hematite and goethite, each characterized by X-ray diffraction (XRD) spectra, and second to controlled mixtures of the two minerals. The results confirm the mineral-diagnostic nature of the experiments used. They are subsequently used to identify goethite and hematite contributions to the rock magnetic properties of a variety of soils and recent sediments. Goethite can be unambiguously identified, often accompanied by hematite, in the majority of the samples studied, despite indications from the synthetic mixtures that the ratio of goethite to hematite may have to exceed an order of magnitude before the goethite signatures are readily recognizable. The rock magnetic tests are a much more sensitive basis for recognizing the presence of goethite in natural samples than are XRD analyses. The results suggest that goethite's contribution to the rock magnetic properties of soil and sediment samples may often have been underestimated.

Release of metals from iron oxyhydroxides under reductive conditions: effect of metal/solid interactions.

Abstract: Solubilization of heavy metals from Fe oxyhydroxides in the presence of sodium ascorbate as a reducing agent were investigated as a function of pH. Amorphous iron hydroxide (HFO) and goethite were synthesized in the presence of Pb, Cd, and Zn, using two different processes, i.e., favoring either metal adsorption (ADS) or metal substitution (coprecipitation, COP). Characterization of solids showed that there were no structural differences among the three kinds of HFO. However, in the case of goethite, it seemed that metal cations were located within the structure of COP goethite, but partially adsorbed in ADS goethite. Results evidenced that, under reductive conditions, the solubilization risk is greater for Pb than for Cd (Cd substituted in the structure) from the coprecipitation process. In the adsorption process, Cd was removed more than Pb (greater complexation constant of Pb). Moreover, irrespective of the crystalline state, solids may be partly dissolved, and release of metals could occur.