Amorphous Iron Hydroxide Research Articles

Natural attenuation reactions at a uranium mill tailings site, western U.S.A.

This paper presents a modeling analysis of the geochemical evolution of a contaminated sandy aquifer at a uranium mill tailings site in the western United States. The tailings pond contains fluids having a pH of 1.5 to 3.5 and high levels of As, Be, Cd, Cr, Pb, Mo, Ni, Se, 226Ra, 228Ra, 230Th, 238U, and 234U. Seepage of tailings fluids into the aquifer has formed a low-pH ground water plume. The reclamation plan is to install a low-permeability cover on the tailings pond to stop the seepage and allow the plume to be attenuated by reactions with the aquifer matrix and flushed by uncontaminated upgradient ground water. To evaluate this reclamation scenario, ground water and sediment core samples were analyzed along one flowpath. Speciation-solubility and mass-transfer modeling revealed two sets of chemical reactions for acid seepage and flushing, respectively. The current concentrations and distribution of ground water constituents can be interpreted as being controlled by stepwise pH-buffer reactions with calcite, amorphous aluminum hydroxide, and amorphous iron hydroxides. These buffer reactions divide the aquifer into zones of near-constant pH, separated by interface zones. For the flushing stage, it is predicted that reactions with surface-bound species will dominate the reaction paths, and more pore volumes are required to neutralize the plume than predicted by models that do not consider surface reactions. Direct mineralogical and surface analysis is needed to substantiate this assertion.

大磯丘陵下末吉埋没土層における腐植酸緑色画分Ｐｇの特性と生成環境

The use of humic acid green fraction (Pg) as a paleoenvironmental indicator still requires integrated case studies applied to tephra and loess soil sequences (Watanabe and Kado, 2000; Watanabe et al., 2001a), as well as biochemical studies on humic acid Pg (Watanabe et al., 2001b). The stability and the chemical transformation of humic acid Pg should be elucidated by investigating paleosols and terrestrial deposits.This study aims to clarify the properties of humic acid green fraction Pg in the Shimosueyoshi buried layer (SB layer), the buried humic soil originating from tephra supplies of Hakone Caldera, corresponding to Marine oxygen isotope stage 5e. Pg absorption strength (Pg abs), total carbon content (TC), carbon content of extracted humic acid (CHA), pH (NaF) value, major element compositions, and phytolith analyses, together with selective dissolution of Fe compounds, and color measurement according to CIE color system were conducted. The obtained results were : 1) Clear Pg absorption bands at around 450, 570, and 615 nm were detected from all the humic acid of paleosols, corresponding to > 100 ka, located at Oiso Hill, central Japan. The fluctuation of Pg abs of humic acid in the investigated profile showed a significant increase in the SB layer (ca. 130 ka), equivalent to the early stage of MIOS 5e.2) According to the measurement error of Pg abs determined through the profile, the significant level of Pg abs in this study is confirmed to be much lower than that of Pg abs in previous studies carried on younger tephra soil sequences. It is considered that humic acid Pg is transformed in paleosols over 100 ka.3) Although the relations among amorphous and crystalline iron hydroxides and Pg absorption strength were not clear in this profile, unlike the previous reports (Kawahigashi et al., 1999, Watanabe and Kobayashi, 2001), the SB layer was characterized by the existence of geothite-like iron hydroxides, suggesting a humid environment.

In-vitro analysis of metallic particles, colloidal nanoparticles and ions in wear-corrosion products of SUS317L stainless steel

The present study attempts to clarify the relative cytotoxic levels of ions, colloidal nanoparticles, and metallic particles found in wear-corrosion products of SUS317L stainless steel. The wear-corrosion products were generated in pin-on-plate wear tests in a calcium-magnesium-free phosphate buffered saline solution (PBS(−)). Of all the particles and ions generated by wear-corrosion, colloidal nanoparticles induced maximum cytotoxicity. Metallic particles were much better tolerated than colloidal nanoparticles. Levels of iron and chromium ions released into the PBS(−) solution were too low to induce cytotoxic effects. Cytotoxic effects due to nickel were still smaller than those due to the colloidal nanoparticles. These nanoparticles consisted mainly of phosphate-containing amorphous iron hydroxide formed by precipitation, and possibly mechanochemical reaction during wear-corrosion.

Hydrogeochemistry of seepage water collected within the Youngcheon diversion tunnel, Korea: source and evolution of SO4‐rich groundwater in sedimentary terrain

AbstractIn the Youngcheon Diversion Tunnel area, South Korea, 46 samples of tunnel seepage water (TSW) and borehole groundwater were collected from areas with sedimentary rocks (mainly sandstone and shale) and were examined for hydrogeochemical characteristics. The measured SO4 concentrations range widely from 7·7 to 942·0 mg/l, and exceed the Korean Drinking Water Standard (200 mg/l) in about half the samples. The TDS (total dissolved solid) content generally is high (171–1461 mg/l) from more shale‐rich formations and also reflects varying degrees of water–rock interaction. The water is classified into three groups: Ca SO4 type (61% of the samples collected), Ca SO4 HCO3 type (15%) and Ca HCO3 type (24%). The Ca HCO3 type water (mean concentrations=369 mg/l Ca, 148 mg/l HCO3 and 23 mg/l SO4) reflected the simple reaction between CO2‐recharged water and calcite, whereas the more SO4‐rich nature of Ca SO4 type water (mean concentrations=153 mg/l Ca, 66 mg/l HCO3 and 416 mg/l SO4) reflected the oxidation of pyrite in sedimentary rocks and fracture zones. Pyrite oxidation resulted in precipitation of amorphous iron hydroxide locally within the tunnel as well as in high concentrations of Ca (mean 153 mg/l) and Na (mean 49 mg/l) for TSW, and is associated with calcite dissolution resulting in pH buffering. The pyrite oxidation required for the formation of Ca SO4 type water was enhanced by the diffusion of oxygenated air through the fractures related to the tunnel's construction. The subsequent outgassing of CO2 into the tunnel resulted in precipitation of iron‐bearing carbonate. Copyright © 2001 John Wiley & Sons, Ltd.

The occurrence of phosphate minerals in lacustrine clayey diatomite deposits, Thessaly, Central Greece

Irregular masses, veins and leaf replacements composed of the phosphate minerals vivianite, mitridatite, anapaite and hydroxylapatite occur in the Sarantaporo–Elassona Upper Miocene lacustrine basin, Thessaly, central Greece. They are hosted in clayey diatomite. Grey to dull green irregular veins of anapaite up to 40 cm thick and spherical concretions up to 2 cm in diameter sporadically occurred at shallow depths. Minor hydroxylapatite rims anapaite masses. Mitridatite occurs in the near surface as greenish-brown veins 5 cm thick, cutting the diatomite or oriented sub-parallel to bedding. The mitridatite veins are rimmed by, and grade into, iron oxides–hydroxides at the surface. In borehole samples, at depths greater than 40 m, bluish vivianite frequently replaces leaves and faecal pellets up to 2 cm in diameter. Conditions permitting the precipitation of phosphate minerals in the basin were the deposition of organic matter, a highly reducing environment at depth (possibly in the lake water but certainly in the bottom sediment), and a low availability of calcium during sedimentation, but its subsequent moderate enrichment in groundwater. The kind of phosphate formed depended on the diagenetic microenvironment. The diagenetic environment was slightly alkaline (8>pH>7). The Ca 2+ /Fe 2+ and Ca 2+ phosphates (i.e. anapaite and hydroxylapatite) that occur at shallow burial depths, most likely formed at the expense of the originally formed Fe 2+ -phosphate vivianite. The progressive substitution of Fe by Ca is attributed to the action of Ca-rich groundwater. The alteration of the ferrous phosphate anapaite to the ferric phosphate mitridatite, plus amorphous iron hydroxides and goethite at the surface, is an indicator of strongly oxidising conditions. The Fe 2+ ions of the phosphates were derived from the leaching of the ultrabasic and schist basement rocks. The absence of calcite in the diatomite reflects the low calcium content of the lake water during sedimentation. The presence of smectite and vermiculite promoted the adsorption of phosphate ions in the sediments of the basin. The accumulation of Fe indicates of the presence of a eutrophic lake environment. The phosphate minerals further suggest stagnant bottom waters and high biological productivity that was promoted by warm–humid conditions.

Release of Metals from Iron Oxyhydroxides under Reductive Conditions: Effect of Metal/Solid Interactions

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.

Factors influencing the measurement of equilibrium phosphate concentrations in river sediments

A river sediment was treated to obtain different oxic conditions, and the phosphorus status investigated by experiments in which KH 2PO 4 was added to suspensions in calcium chloride. The pH, redox and solution composition of dissolved Ca, Mg, Fe, Na, K, Mn, Cl and SO 4 and soluble reactive phosphorus were measured at the end of 24 h mixing. The equilibrium phosphate concentration was calculated from these measurements using the linear, Freundlich and dual-site Langmuir isotherm equations. The chemical speciation of the solutions was evaluated using PHREEQC and a model designed specifically for phosphorus speciation. These were used to estimate the solution saturations with respect to various iron and calcium containing minerals. The results show that at least a two-fold increase in the calculated equilibrium phosphate concentration of the sediment occurs with a moderate change in the electron activity from 8 to 4 as the sediments became reducing. Chemical precipitation and dissolution reactions were also found to be important during the experiments, with dissolved iron concentrations in oxic conditions determined by equilibration with amorphous iron hydroxide. Only in the suspensions with the highest soluble reactive phosphorus concentration was the solubility limit of ferric phosphate approached. There was also evidence for the loss of calcium from the solutions and oversaturation with respect to octacalcium phosphate. Vivianite, found in the sediment, was also expected to dissolve in the most oxic conditions. It is proposed that ancillary measurements of pH, redox potential, dissolved Ca, Fe, Mn and alkalinity during equilibrium phosphate concentration determinations will provide a better understanding to the buffering reactions controlling phosphorus in solutions in contact with sediments.

Volume Changes Due to SO2−4, SeO2−4, and H2PO−4Adsorption on Amorphous Iron(III) Hydroxide in an Aqueous Suspension

Volume changes due to SO2−4, SeO2−4, and H2PO−4adsorption on amorphous iron(III) hydroxide were determined by dilatometry in a mixture comprising an aqueous solution of Na2SO4, Na2SeO4, or NaH2PO4and amorphous iron(III) hydroxide suspended in 0.1 mol dm−3NaClO4at an initial pH ranged from 4.50 to 6.50. System volumes increased during SO2−4, SeO2−4, and H2PO−4adsorption on amorphous iron(III) hydroxide, suggesting that some hydrated water around aqueous SO2−4, SeO2−4, or H2PO−4ions and amorphous iron(III) hydroxide were released to the bulk. The volume changes due to SO2−4, SeO2−4, and H2PO−4adsorption at initial pH 4.50 were +18, +18, and +14 cm3mol−1, respectively. Phosphate, which adsorbed as an inner-sphere complex, released most of its hydration water to the bulk. The volume changes due to SO2−4and SeO2−4adsorption indicated that they were dehydrated at the water/amorphous iron(III) hydroxide interface. The smaller changes in volume for H2PO−4compared to SO2−4and SeO2−4may be explained by differences of charges and adsorption mechanisms of these oxoanions.

Hydroxamate siderophores, cell growth and Fe(III) cycling in two anaerobic iron oxide media containing Geobacter metallireducens

We test the hypothesis that a versatile strain of iron bacteria, Geobacter metallireducens, can metabolize Fe(III) when it is complexed to hydroxamate ligands. Pure cultures were grown under anaerobic conditions with, and without, a Fe(III)(tris)acetohydroxamic acid complex as a source of Fe(III). These experiments were conducted with goethite [α-FeOOH] and amorphous iron hydroxide [Fe(OH) 3(s)] to determine whether hydroxamate ligands can stimulate cell growth by dissolving Fe(III) from the mineral surface. We found that solids reduced the bacterial activity by lowering dissolved Fe(III) concentrations relative to solid-free medium. Acetohydroxamate did not significantly enhance cell growth, possibly because the Fe(III) was too difficult to reduce when complexed in a trihydroxamate complex. The hydroxamate ligand also had a dramatic effect on the cell morphology, such cell numbers could be used as a measure of microbial activity in solutions with this ligand, and there is evidence for an abiotic pathway for Fe(II) oxidation in the media containing hydroxamate.

Porewater dynamics and the formation of iron sulfides in a mangrove ecosystem, Sepetiba Bay, Brazil

Porewater dynamics and the formation of iron sulfides were studied in the Brazilian mangrove. Porewater samples were collected during tidal cycles using in situ equipment and physical–chemical and chemical data were obtained. The advective transport of porewater by tidal currents was found to be more effective between 0 and 5 cm depth than below 15 cm. The diffusive input of atmospheric oxygen during low tides resulted in oxidation of porewater dissolved sulfides. Thermodynamic considerations identified pyrite as the main iron sulfide forming at this depth, and the amorphous iron hydroxides are probably the main iron source. Below 15 cm depth, irregular root distribution underground and benthic faunal bioturbation caused considerable spatial variation in a small scale (20 cm). The correlation between alkalinity and total dissolved sulfide suggests that the main pathway for organic matter decomposition is sulfate reduction. Formed in the highly sulfidic diagenetic zone, the dissolved iron went through iron sulfide formation process. Crystalline iron oxides like hematite and magnetite may constitute an important iron source below 15 cm, whereas pyrite is still the most probably occurring iron sulfide, according to thermodynamic considerations.

Fenton-Like Soil Remediation Catalyzed by Naturally Occurring Iron Minerals

The ability of the iron minerals hematite and magnetite to catalyze the decomposition of hydrogen peroxide (H2O2) and initiate the Fenton-like oxidation of pentachlorophenol (PCP) was investigated in batch, bench-scale systems in which PCP was spiked onto silica sand. Pentachlorophenol degradation was documented in silica sand–mineral–H2O2 systems by the release of chloride and the loss of total organic carbon. The most efficient oxidation stoichiometry was the magnetite-catalyzed reaction over the first 8 h with 490 mol H2O2 consumed/mol PCP degraded. After 8 h, the peroxide efficiency decreased significantly; amorphous iron hydroxide formation on the magnetite surface may have catalyzed the decomposition of H2O2 to oxygen species other than hydroxyl radicals. Mineral-catalyzed Fenton-like treatment in two natural soils was demonstrated after spiking the soils with PCP; the contaminant was degraded with no iron addition. The oxidation stoichiometry in the two soils was 1,100 and 2,930 mol H2O2 consumed/mol PCP degraded. Key words: Advanced oxidation processes; Fenton's reagent; hydrogen peroxide; iron oxyhydroxides; pentachlorophenol; soil remediation

Iron-Oxide Supported Gold Catalysts Derived from Gold-Phosphine Complex Au(PPh3)(NO3): State and Structure of the Support

Iron oxide supported gold catalysts were prepared by supporting the Au-phosphine complex Au(PPh3)(NO3) onto various iron oxide supports. Among the prepared catalysts only the use of amorphous as-precipitated iron hydroxide Fe(OH)*3as a support for Au(PPh3)(NO3) allowed us to obtain the tremendously active catalytic material for low-temperature CO oxidation. The supports and the Au catalysts were characterized by BET, SEM, XRD, FT-IR, XPS, and Raman. Initial structures of the employed supports were found to influence dramatically the gold particle size and the catalytic activity. The most active catalyst consisted of small gold particles and poorly crystallized iron oxide support with a mixture of α-Fe2O3and γ-Fe2O3. The γ-Fe2O3formation occurred by the presence of the PPh3as a ligand for gold. The presence of γ-Fe2O3influenced positively the catalytic activity of the Au-containing samples.

Estudio de la reactividad de soluciones sólidas jarosita-beudantita por sulfuración-cianuración

The jarositic materials occurs as ores (such as gossan) or as residues from some hydrometallurgical processes. To recover silver contained in these materials, processes of alkaline decompositioncyanidation at room or high temperatures or under pressure have been proposed. A sulphidizingcyanidation study of jarosite-beudantite solid solutions from gossan ores is presented. The solid transformations have been determined using X-ray diffraction, optical and electron microscopy (SEM-EDS) and electron microprobe. During the first step of the process the jarosite phases are decomposed with the formation of lead and silver sulphides and amorphous iron hydroxide. The decomposition of potassium jarosite-beudantite and beudantite-plumbojarosite are carried out at pH ≥ 12 and pH = 14, respectively. An oxidation, to remove the excess of sulphide, followed by the conventional cyanidation process leads to the recovery of the silver.

Ferric hydroxide and ferric hydroxysulfate precipitation by bacteria in an acid mine drainage lagoon

The spontaneous precipitation of amorphous iron hydroxide and ferric hydroxysulfate has generally been considered to be an inorganic process involving the oxidation of ferrous iron with or without the presence of sulfate. However, our study of bacterial communities growing in an acid mine drainage lagoon sediment has confirmed that microorganisms were also capable of facilitating this mineral precipitation. Transmission electron microscopy revealed that bacteria growing at the surface had iron-rich capsules, along with detectable amounts of Zn, Ti, Mn and K incorporated into the mineralised matrix. In the subsurface, more cells were associated with granular, fine-grained mineral precipitates, composed almost exclusively of iron and sulfur. Pore water profiles indicated that no discernible sulfate reduction had taken place, suggesting that these authigenic minerals were ‘ferric hydroxysulfate’, and not iron sulfide. Energy dispersive X-ray spectroscopy further indicated that the subsurface minerals had variable composition, with the Fe:S ratio decreasing with depth from 3.5:1 at 15 cm to 1.9:1 at 30 cm. This indicates the high reactivity of ferric hydroxide for dissolved sulfate. Because iron reduction was limited to sediment depths between 3–10 cm, it is conceivable that these minerals are not amenable to bacterial reduction, and hence, the ability of bacteria to bind and form such precipitates may provide a natural solution to cleansing acidified waters with a high dissolved metal content.

Geochemical modeling of coal mine drainage, Summit County, Ohio

Geochemical modeling was used to investigate downstream changes in coal mine drainage at Silver Creek Metro-park, Summit County, Ohio. A simple mixing model identified the components that are undergoing conservative transport (Cl–, PO43–, Ca2+, K+, Mg2+ and Na+) and those undergoing reactive transport (DO, HCO3–, SO42–, Fe2+, Mn2+ and Si). Fe2+ is removed by precipitation of amorphous iron-hydroxide. Mn2+ are removed along with Fe2+ by adsorption onto surfaces of iron-hydroxides. DO increases downstream due to absorption from the atmosphere. The HCO3– concentration increases downstream as a result of oxidation of organic material. The rate of Fe2+ removal from the mine drainage was estimated from the linear relationship between Fe+2 concentration and downstream distance to be 0.126 mg/s. Results of this study can be used to improve the design of aerobic wetlands used to treat acid mine drainage.

Desulfospira joergensenii, gen. nov., sp. nov., a new Sulfate-reducing Bacterium Isolated from Marine Surface Sediment

Summary A new Gram-negative sulfur-reducing eubacterium was isolated from iron-rich oxidized marine surface sediment with elemental sulfur and butyrate. Elemental sulfur can be substituted by sulfate. In addition, thiosulfate and sulfite are used as electron acceptors. The strain, named B331, grows well in hydrogen sulfide free medium in the presence of high concentrations of amorphous iron (FeIII) hydroxide. The substrate spectrum is versatile and includes hydrogen, fatty acids, dicarboxylic acids, oxoacids, hydroxyacids, compatible solutes (choline, chloride, betaine, glycerol and proline) and yeast extract. A fermentative type of metabolism was not observed. The cells are vibrio-shaped and not motile. The G+C content of the genomic DNA is 49.3 mol%. Cytochromes are present, desulfoviridin is not. The major lipoquinones present are menaquinones including both MK-7 and MK-7(VII-H2). The fatty acid composition comprises mainly unbranched fatty acids. The major polar lipids are phosphatidyl glycerol and phosphatidyl ethanolamine. Comparative 16S rDNA sequence analysis placed strain B331 into the delta subgroup of proteobacteria originating in a common root with members of the genera Desulfobacter and Desulfobacula. Within this group it forms a distinct line of descent with Desulfobacula toluolica as the most closely related microorganism. Strain B331 is described as the type species and type strain, respectively, of a new taxon, Desulfospira joergensenii gen. nov., sp. nov.

Volume Changes in an Aqueous Suspension of Amorphous Iron(III) Hydroxide Due to the Adsorption of Phosphates (H2PO−4)

Volume changes on H2PO−4adsorption with amorphous iron(III) hydroxide were determined in a mixture of aqueous solutions of phosphates (NaH2PO4) and suspended amorphous iron(III) hydroxide at an initial pH of 5.50 or 4.50, at 298 K. Volume changes were determined by a dilatometer after the mixing of phosphate solutions and suspended amorphous iron(III) hydroxide solutions. The increased volumes of the systems after the mixing of H2PO−4solutions and suspended amorphous iron(III) hydroxide suggested that H2PO−4adsorption was accompanied by dehydration of aqueous H2PO−4ions and suspended amorphous iron(III) hydroxide in water. The estimated volume changes per mole of H2PO−4adsorption were about +15 cm3.

Interaction of sodium dodecylsulfate (SDS) with homoionic montmorillonites: adsorption isotherms and metal-ion release

The interaction of dodecylsulfate anions (DS−) with homoionic Ca-, Mg-, Ni-, Cu-, Cd-, Pb- and Fe-montmorillonites were investigated. Mg- and Cd-montmorillonite do not adsorb DS−, and an anion exchange at the edges of the clay mineral does not take place. Three different adsorption processes are identified on the other montmorillonites: i) Fe-montmorillonite is covered with amorphous iron hydroxide, and DS−-anions are bound at positively charged sites. ii) On Ca- and Pb-montmorillonite DS− is precipitated as Me(DS)2. iii) On Ni- and Cu-montmorillonite DS− forms ion pairs with the cations on the surface. In all cases DS− is not bound above the CMC but the metal ions are mobilized from the surface either by solubilization of the precipitates or by formation of mixed micelles.

Characterization of iron(III) oxide and oxide-hydroxide as Sr-sorbent

Iron(III) hydroxide and oxide-hydroxide samples prepared by precipitation of 0.2M iron(III) nitrate solution by 5M NaOH and subsequently aged at pH 12 for times of up to 50 h have been characterized. The sorption properties towards Sr2+ were characterized by radiotracer method using85Sr, morphology of the samples was characterized by Transmission Electron Microscopy and Emanation Thermal Analysis. X-ray diffraction patterns characterized the crystallinity of the samples aged for various times. The maximum (100%) sorption capacity for85Sr corresponding to amorphous iron(III) hydroxide decreased to 75% with the time of precipitate ageing (up to 40 h). This finding corresponds to the development in crystallinity and morphology of the sorbent.

Study on the Interaction between Iron(III) Hydroxide Oxide and Cation Exchange Resins

Abstract In some nuclear power plants, ion exchange resins for condensate purification systems show increasing rust removal efficiency year by year. In order to clarify this phenomenon, resin properties and rust behavior after adsorption on the resins have been studied. An adsorption test, a dissolution test and an ion exchanging test were performed in this study, using strongly acidic cation exchange resins, amorphous iron(III) hydroxide oxide and 55Fe tracer. It was found that aged cation exchange resins showed obvious property changes due to oxidative swelling, which induced better water mobility in the micropores. According to the property change, amorphous iron(III) hydroxide oxide, one of the iron rust components, is easily dissolved and diffused into resin beads, and consequently adsorption sites on aged resins are recovered rapidly compared with fresh resins. This is the reason for the superiority of the aged cation exchange resins in rust removal.