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1.
Fe(III) solid phases are the products of Fe(II) oxidation by Fe(II)-oxidizing bacteria, but the Fe(III) phases reported to form within growth experiments are, at times, poorly crystalline and therefore difficult to identify, possibly due to the presence of ligands (e.g., phosphate, carbonate) that complex iron and disrupt iron (hydr)oxide precipitation. The scope of this study was to investigate the influences of geochemical solution conditions (pH, carbonate, phosphate, humic acids) on the Fe(II) oxidation rate and Fe(III) mineralogy. Fe(III) mineral characterization was performed using 57Fe-Mössbauer spectroscopy and μ-X-ray diffraction after oxidation of dissolved Fe(II) within Mops-buffered cell suspensions of Acidovorax sp. BoFeN1, a nitrate-reducing, Fe(II)-oxidizing bacterium. Lepidocrocite (γ-FeOOH) (90%), which also forms after chemical oxidation of Fe(II) by dissolved O2, and goethite (α-FeOOH) (10%) were produced at pH 7.0 in the absence of any strongly complexing ligands. Higher solution pH, increasing concentrations of carbonate species, and increasing concentrations of humic acids promoted goethite formation and caused little or no changes in Fe(II) oxidation rates. Phosphate species resulted in Fe(III) solids unidentifiable to our methods and significantly slowed Fe(II) oxidation rates. Our results suggest that Fe(III) mineralogy formed by bacterial Fe(II) oxidation is strongly influenced by solution chemistry, and the geochemical conditions studied here suggest lepidocrocite and goethite may coexist in aquatic environments where nitrate-reducing, Fe(II)-oxidizing bacteria are active.  相似文献   

2.
The behaviour of trace amounts of arsenate coprecipitated with ferrihydrite, lepidocrocite and goethite was studied during reductive dissolution and phase transformation of the iron oxides using [55Fe]- and [73As]-labelled iron oxides. The As/Fe molar ratio ranged from 0 to 0.005 for ferrihydrite and lepidocrocite and from 0 to 0.001 for goethite. For ferrihydrite and lepidocrocite, all the arsenate remained associated with the surface, whereas for goethite only 30% of the arsenate was desorbable. The rate of reductive dissolution in 10 mM ascorbic acid was unaffected by the presence of arsenate for any of the iron oxides and the arsenate was not reduced to arsenite by ascorbic acid. During reductive dissolution of the iron oxides, arsenate was released incongruently with Fe2+ for all the iron oxides. For ferrihydrite and goethite, the arsenate remained adsorbed to the surface and was not released until the surface area became too small to adsorb all the arsenate. In contrast, arsenate preferentially desorbs from the surface of lepidocrocite. During Fe2+ catalysed transformation of ferrihydrite and lepidocrocite, arsenate became bound more strongly to the product phases. X-ray diffractograms showed that ferrihydrite was transformed into lepidocrocite, goethite and magnetite whereas lepidocrocite either remained untransformed or was transformed into magnetite. The rate of recrystallization of ferrihydrite was not affected by the presence of arsenate. The results presented here imply that during reductive dissolution of iron oxides in natural sediments there will be no simple correlation between the release of arsenate and Fe2+. Recrystallization of the more reactive iron oxides into more crystalline phases, induced by the appearance of Fe2+ in anoxic aquifers, may be an important trapping mechanism for arsenic.  相似文献   

3.
Microbial sulfidogenesis plays a potentially important role in Fe and As biogeochemistry within wetland soils, sediments and aquifers. This study investigates the specific effects of microbial sulfidogenesis on Fe mineralogy and associated As mobility in mildly acidic (pH 6) and mildly basic (pH 8) advective-flow environments. A series of experiments were conducted using advective-flow columns, with an initial solid-phase comprising As(III)-bearing ferrihydrite-coated quartz sand. Columns for each pH treatment were inoculated with the sulfate-reducing bacteria Desulfovibrio vulgaris, and were compared to additional abiotic control columns. Over a period of 28 days, microbial sulfidogenesis (as coupled to the incomplete oxidation of lactate) caused major changes in Fe mineralogy, including replacement of ferrihydrite by mackinawite and magnetite at the in-flow end of the inoculated columns. At pH 8, the Fe2+ produced by electron transfer between sulfide and ferrihydrite was mainly retained near its zone of formation. In contrast, at pH 6, much of the produced Fe2+ was transported with advecting groundwater, facilitating the downstream Fe2+-catalyzed transformation of ferrihydrite to goethite. At both pH 6 and pH 8, the sulfide-driven reductive dissolution of ferrihydrite and its replacement by mackinawite at the in-flow end of the inoculated columns resulted in substantial mobilization of As into the pore-water. At pH 8, this caused the downstream As concentrations within the inoculated columns to be greater than the corresponding abiotic column. However, the opposite occurred under pH 6 conditions, with the Fe2+-catalyzed transformation of ferrihydrite to goethite in the inoculated columns causing a decrease in downstream As concentrations compared to the abiotic column. Although thermodynamically favorable at intermediate times and depth intervals within the inoculated columns, solid As sulfide phases were undetectable by As XANES spectroscopy. Our findings show that microbial sulfidogenesis can trigger significant As mobilization in subsurface environments with advective groundwater flow. The results also demonstrate that formation of mackinawite by sulfidization of ferric (hydr)oxides is not effective for the immobilization of As, whereas the Fe2+-catalyzed transformation of ferrihydrite to goethite under mildly acidic conditions may mitigate As mobility.  相似文献   

4.
The mineralogical and chemical evolution of ochreous precipitates forming from acid mine drainage (AMD) from the abandoned Libiola Fe–Cu-sulfide mine (Eastern Liguria, Italy) was followed through a multianalytical approach (XRD, TEM, XRF, ICP) applied to surface precipitates and associated waters collected from several mine adits. The mineralogy of the precipitates changed significantly as a consequence of the variations of the chemical parameters of the circulating solutions (mainly pH, Eh, and sulfate concentrations) which, in turn, were mainly controlled by mixing with unpolluted stream and rill waters of the mining area. A progressive transition from jarosite-, to schwertmannite-, to goethite-, to ferrihydrite-, to amorphous-dominated precipitates was observed, mainly as a consequence of an increase in the pH of the associated solutions. This mineralogical evolution agrees well with the aqueous speciation and Eh–pH stability calculations performed on the waters associated with the different precipitate types. Furthermore, TEM analysis indicated that metastable pristine phases (schwertmannite) tend to transform progressively to well-crystallized more stable species, here represented by goethite. The comparison of the water chemistry and the crystal chemistry of the different precipitates showed a significant decrease in the Zn, Cu, Ni, Co contents in waters where the coexisting precipitates were almost exclusively composed of goethite. The distribution of V, Sr, As concentrations within the different precipitates showed that the most efficient scavenging phase for these elements was jarosite, whereas ferrihydrite efficiently took up Pb ions, and schwermannite acted as a natural sink for Cr.  相似文献   

5.
Aluminum, one of the most abundant elements in soils and sediments, is commonly found co-precipitated with Fe in natural Fe(III) (hydr)oxides; yet, little is known about how Al substitution impacts bacterial Fe(III) reduction. Accordingly, we investigated the reduction of Al substituted (0-13 mol% Al) goethite, lepidocrocite, and ferrihydrite by the model dissimilatory Fe(III)-reducing bacterium (DIRB), Shewanella putrefaciens CN32. Here we reveal that the impact of Al on microbial reduction varies with Fe(III) (hydr)oxide type. No significant difference in Fe(III) reduction was observed for either goethite or lepidocrocite as a function of Al substitution. In contrast, Fe(III) reduction rates significantly decreased with increasing Al substitution of ferrihydrite, with reduction rates of 13% Al-ferrihydrite more than 50% lower than pure ferrihydrite. Although Al substitution changed the minerals’ surface area, particle size, structural disorder, and abiotic dissolution rates, we did not observe a direct correlation between any of these physiochemical properties and the trends in bacterial Fe(III) reduction. Based on projected Al-dependent Fe(III) reduction rates, reduction rates of ferrihydrite fall below those of lepidocrocite and goethite at substitution levels equal to or greater than 18 mol% Al. Given the prevalence of Al substitution in natural Fe(III) (hydr)oxides, our results bring into question the conventional assumptions about Fe (hydr)oxide bioavailability and suggest a more prominent role of natural lepidocrocite and goethite phases in impacting DIRB activity in soils and sediments.  相似文献   

6.
The Me?a River Valley has been a center of mining, ore processing and iron- and steel-based metallurgical industry for more than 300 a. This paper deals with stream sediments draining this area. Loads of potentially toxic metals and metal-bearing phases were investigated 10 a after the cessation of Pb and Zn mining. Sediments in the upper Me?a River Valley show significant pollution with Pb and Zn as a consequence of mining and ore processing. The highest contents of Pb and Zn were found in the Me?a tributaries, which directly drain mine waste deposits (maximum values: 19,300 mg/kg Pb and 37,900 mg/kg Zn). These results reflect transport of contaminated material from mine waste sites and indicate that the inactive mine and its mine wastes are sources of metal contamination in the surrounding environment. Contents of Cr, Ni, Cu and Co are increased in the lower Me?a River Valley, in the area of Ravne, as a result of the iron and steel industry. The contribution of the Me?a River to the metal-load in the Drava River is evident.Metal-bearing phases, identified in stream sediments by SEM/EDS, are assigned to three areas, according to their source and genesis. The Me?ica mining district source area is characterized by ore minerals of geogenic/technogenic origin (cerussite, sphalerite, smithsonite and galena), the Ravne source area is characterized by technogenic trace metal-bearing Fe-alloys, Fe-oxides and spherical trace metal-oxides and the Me?a and Drava River catchment areas are represented by geogenic metal-bearing accessory and common rock-forming minerals, such as zircon, ilmenite, rutile, sphene, barite and monazite. SEM/EDS analyses of stream sediments agree well with the results of chemical analyses and they prove to be a very useful tool for identification of metal-bearing phases and their characterization according to source and genesis.  相似文献   

7.
To remediate Pb contaminated soils it is proposed that phosphorus can be amended to the soils to transform the Pb into poorly soluble Pb-phosphate mineral phases. However, remediation strategies must account for variable Pb speciation and site-specific factors. In this study soil mineralogy and Pb speciation in soils from P-amended field trials at sites within the Coeur d’Alene River Basin in Idaho, USA were investigated. The soils are contaminated from mining activities and are enriched with Fe and Mn. Selective extraction of the soils indicated that the Fe oxides are poorly crystalline. XRD of the soil clay size fractions identified quartz, muscovite, kaolinite, siderite, lepidocrocite, and chlorite minerals. Amendment with P fertilizer dissolved the siderite. No Pb–phosphate minerals were detected by XRD. Electron microprobe analysis showed direct correlations between Pb, Fe, and Mn in the unamended soils, and negative correlations between Pb and Si. Lead and Mn were strongly correlated. In the amended soils Fe and P were strongly correlated. Results indicate that the Pb is associated with poorly crystalline Fe and Mn oxides, and that added P is primarily associated with Fe oxide phases. Comparisons of pore water Pb concentrations with chloropyromorphite and plumbogummite solubility suggest that in the phosphate-amended soils the pore waters are undersaturated in these phases, whereas several of the control soil pore waters were oversaturated, indicating the added phosphate suppressed the Pb solubility. Results from this research provide insight into the geochemistry occurring in the P-remediated soils that will help in making management and remediation decisions.  相似文献   

8.
《Geochimica et cosmochimica acta》1999,63(19-20):2971-2987
Many sediment and soil systems have become significantly contaminated with cadmium, and earth scientists are now required to make increasingly accurate predictions of the risks that this contamination poses. This necessitates an improved understanding of the processes that control the mobility and bioavailability of cadmium in the environment. With this in mind, we have studied the composition and structure of aqueous cadmium sorption complexes on the iron oxyhydroxide minerals goethite (α-FeOOH), lepidocrocite (γ-FeOOH), akaganeite (β-FeOOH), and schwertmannite (Fe8O8(OH)6SO4) using extended X-ray adsorption fine structure spectroscopy. The results show that adsorption to all of the studied minerals occurs via inner sphere adsorption over a wide range of pH and cadmium concentrations. The bonding mechanism varies between minerals and appears to be governed by the availability of different types of adsorption site at the mineral surface. The geometry and relative stability of cadmium adsorption complexes on the goethite surface was predicted with ab initio quantum mechanical modelling. The modelling results, used in combination with the extended X-ray adsorption fine structure data, allow an unambiguous determination of the mechanism by which cadmium bonds to goethite.Cadmium adsorbs to goethite by the formation of bidentate surface complexes at corner sharing sites on the predominant (110) crystallographic surface. There is no evidence for significant cadmium adsorption to goethite at the supposedly more reactive edge sharing sites. This is probably because the edge sharing sites are only available on the (021) crystallographic surface, which comprises just ∼2% of the total mineral surface area. Conversely, cadmium adsorption on lepidocrocite occurs predominately by the formation of surface complexes at bi- and/or tridentate edge sharing sites. We explain the difference in extended X-ray adsorption fine structure results for cadmium adsorption on goethite and lepidocrocite by the greater availability of reactive edge sharing sites on lepidocrocite than on goethite. The structures of cadmium adsorption complexes on goethite and lepidocrocite appear to be unaffected by changes in pH and surface loading. There is no support for cadmium sorption to any of the studied minerals via the formation of an ordered precipitate, even at high pH and high cadmium concentration. Cadmium adsorption on akaganeite and schwertmannite also occurs via inner sphere bonding, but the mechanism(s) by which this occurs remains ambiguous.  相似文献   

9.
《Applied Geochemistry》2006,21(3):437-445
Oxidation of FeS2 in mine waste releases SO42-, Fe(II) and H+, resulting in acid mine drainage (AMD). Subsequent oxidation and precipitation of Fe produces different Fe(III) phases where the mineralogical composition depends on pH and the ambient concentrations of metal ions and complexing ligands. The oxidation and precipitation of Fe in AMD has been studied under various conditions with the intent of understanding the role these processes play in the natural attenuation of metal contaminants in the AMD. The combined process of Fe oxidation and precipitation in AMD from the Kristineberg mine, northern Sweden, has been investigated with pH-stat experiments at pH 5.5 and 7 at 10 and 25 °C. The precipitates formed have been characterised in terms of mineralogy and surface area. Similar phases formed at both temperatures, while the oxidation and precipitation occurred more readily at the higher temperature and higher pH. At pH 7, mainly lepidocrocite (γ-FeOOH) was precipitated while at a lower pH of 5.5, a mixture of schwertmannite, goethite, ferrihydrite and lepidocrocite formed. The ambient Zn(II) concentration was immediately reduced to acceptable levels (according to Swedish EPA) at pH 7 whereas a 2–3 weeks ageing period was necessary to achieve the same effect at pH 5.5. The presence of natural organic matter (NOM) reduced the attenuating effect at pH 5.5 after ageing but increased it slightly at pH 7. Addition of Zn(II) at pH 8 resulted in a mixed Fe(III)–Zn(II) precipitate of unknown composition with some Zn(II) adsorbed at the surface. The Fe(III) precipitates formed are potentially useful for the natural attenuation of metal contaminants in AMD although based on these investigations, the degree of success depends upon pH and NOM concentration.  相似文献   

10.
Oxidation of mackinawite (FeS) and concurrent mobilization of arsenic were investigated as a function of pH under oxidizing conditions. At acidic pH, FeS oxidation is mainly initiated by the proton-promoted dissolution, which results in the release of Fe(II) and sulfide in the solution. While most of dissolved sulfide is volatilized before being oxidized, dissolved Fe(II) is oxidized into green rust-like precipitates and goethite (α-FeOOH). At basic pH, the development of Fe(III) (oxyhydr)oxide coating on the FeS surface inhibits the solution-phase oxidation following FeS dissolution. Instead, FeS is mostly oxidized into lepidocrocite (γ-FeOOH) via the surface-mediated oxidation without dissolution. At neutral pH, FeS is oxidized via both the solution-phase oxidation following FeS dissolution and the surface-mediated oxidation mechanisms. The mobilization of arsenic during FeS oxidation is strongly affected by FeS oxidation mechanisms. At acidic pH (and to some extent at neutral pH), the rapid FeS dissolution and the slow precipitation of Fe (oxyhydr)oxides results in arsenic accumulation in water. In contrast, the surface-mediated oxidation of FeS at basic pH leads to the direct formation of Fe (oxyhydr)oxides, which provides effective adsorbents for As under oxic conditions. At acidic and neutral pH, the solution-phase oxidation of dissolved Fe(II) accelerates the oxidation of the less adsorbing As(III) to the more adsorbing As(V). This study reveals that the oxidative mobilization of As may be a significant pathway for arsenic enrichment of porewaters in sulfidic sediments.  相似文献   

11.
The numerous non-sulfide zinc ore deposits were the historical basis for the development of zinc mining in Iran.They include the Mehdiabad,Irankouh and Angouran world-class deposits,as well as the Zarigan and Haft-har deposits.These deposits were formed by supergene oxidation of primary sulfide minerals during the complex interplay of tectonic uplift,karst development,changes in the level of the water table,and weathering.Zn(Pb)carbonates,Zn-hydrosilicates and associated hydrated phases directly replace the primary ore bodies or fill cavities along fractures related to uplift tectonics.Direct replacement of primary sulfides is accompanied by distal precipitation of zinc non-sulfide minerals in cavities or internal sediments filling.The mineralogy of the non-sulfide mineralization in all six deposits is generally complex and consists of smithsonite,hydrozincite,and hemimorphite as the main economic minerals,accompanied by iron and manganese oxy-hydroxides and residual clays.Commonly,non-sulfide minerals in these deposits consist of two types of ore:red zinc ore(RZO),rich in Zn,Fe,Pb-(As)and white zinc ore(WZO),typically with very high zinc grades but low concentrations of iron and lead.Typical minerals of the RZO are Fe-oxyhydroxides,goethite,hematite,hemimorphite,smithsonite and/or hydrozincite and cerussite.Common minerals of the WZO are smithsonite or hydrozincite and only minor amounts of Fe-oxyhydroxides and hemimorphite.  相似文献   

12.
The redox properties of FeII adsorbed onto a series of FeIII (oxyhydr)oxides (goethite, lepidocrocite, nano-sized ferric oxide hydrate (nano-FOH), and hydrous ferric oxide (HFO)) have been investigated by rest potential measurements at a platinum electrode, as a function of pH (−log10[H+]) and surface coverage. Using the constant capacitance surface complexation model to describe FeII adsorption onto these substrates, theoretical values of the suspension redox potential (EH) have been computed, under the assumption that FeII adsorption occurs at crystal growth sites of the substrate surface. Good agreement between calculated and experimental EH values is observed for nano-FOH and HFO, however the redox potentials measured for lepidocrocite and goethite are significantly more oxidizing than predicted. Mössbauer spectroscopic analysis of 57FeII adsorbed onto HFO and goethite shows that in both cases the adsorbed 57FeII is incorporated into the crystal structure of the substrate, in broad agreement with the thermodynamic model, but is almost completely oxidized to 57FeIII. The mechanism by which the adsorbed 57FeII is oxidized is not resolved in this work, but is thought to be due to electron transfer to the substrate, rather than a net oxidation of the suspension. The disagreement between experimental and calculated rest potential measurements in the goethite and lepidocrocite systems is thought to be due to the poor electrochemical equilibration of these suspensions with the platinum electrode, rather than a failure of the thermodynamic model. The model developed for the redox potential of adsorbed FeII allows direct assessment of the reactivity of this species towards oxidized pollutants.  相似文献   

13.
By R-mode factor analysis and enrichment factor calculations, most of the elements in abyssal ferromanganese nodules and associated pelagic sediments (excluding common authigenic minerals like apatite, barite, opal and carbonates) are found to be preferentially concentrated in one of the following three major phases: aluminosilicates (e.g., Al, Si, Sc, Ga, Cr, Be, Na, K, Rb and Cs), Fe-oxides (e.g., Fe, P, S, V, Se, Te, As, B, Sn, U, Hg, Pb, Ti, Ge, Y, Zr, Nb, Pd, In, rare-earths, Hf, Th, Pa, Pu, Am, Ru and Bi), and Mn-oxides (e.g., Mn, Tl, Ag, Cd, Mg, Ca, Ba, Ra, Co, Ni, Cu, Zn, Mo, Sb and probably W). The specific association of elements with these three phases can be explained by the difference in chemical forms of elements in seawater and by fundamental differences in physicochemical properties (e.g., the pH of zero point of charge and dieletric constant) of these three phases.  相似文献   

14.
《Geochimica et cosmochimica acta》1999,63(19-20):3003-3008
Hydroxamate siderophores are biologically-synthesized, Fe(III)-specific ligands which are common in soil environments. In this paper, we report an investigation of their adsorption by the iron oxyhydroxide, goethite; their influence on goethite dissolution kinetics; and their ability to affect Pb(II) adsorption by the goethite surface. The siderophores used were desferrioxamine B (DFO-B), a fungal siderophore, and desferrioxamine D1, an acetyl derivative of DFO-B (DFO-D1). Siderophore adsorption isotherms yielded maximum surface concentrations of 1.5 (DFO-B) or 3.5 (DFO-D1) μmol/g at pH 6.6, whereas adsorption envelopes showed either cation-like (DFO-B) or ligand-like (DFO-D1) behavior. Above pH 8, the adsorbed concentrations of both siderophores were similar. The dissolution rate of goethite in the presence of 240 μM DFO-B or DFO-D1 was 0.02 or 0.17 μmol/g hr, respectively. Comparison of these results with related literature data on the reactions between goethite and acetohydroxamic acid, a monohydroxamate ligand, suggested that the three hydroxamate groups in DFO-D1 coordinate to Fe(III) surface sites relatively independently. The results also demonstrated a significant depleting effect of 240 μM DFO-B or DFO-D1 on Pb(II) adsorption by goethite at pH > 6.5, but there was no effect of adsorbed Pb(II) on the goethite dissolution rate.  相似文献   

15.
Iron oxides may undergo structural transformations when entering an anoxic environment. These transformations were investigated using the isotopic exchange between aqueous Fe(II) and iron oxides in experiments with 55Fe-labelled iron oxides. 55Fe was incorporated congruently into a ferrihydrite, two lepidocrocites (#1 and #2), synthesised at 10°C and 25°C, respectively, a goethite and a hematite. The iron oxides were then submerged in Fe2+ solutions (0-1.0 mM) with a pH of 6.5. In the presence of aqueous Fe2+, an immediate and very rapid release of 55Fe was observed from ferrihydrite, the two lepidocrocites and goethite, whereas in the absence of Fe2+ no release was observed. 55Fe was not released from hematite, even at the higher Fe2+ concentration. The release rate is mainly controlled by characteristics of the iron oxides, whereas the concentration of Fe2+ only has minor influence. Ferrihydrite and 5-nm-sized lepidocrocite crystals attained complete isotopic equilibration with aqueous Fe(II) within days. Within this timeframe ferrihydrite transformed completely into new and more stable phases such as lepidocrocite and goethite. Lepidocrocite #2 and goethite, having larger particles, did not reach isotopic equilibrium within the timeframe of the experiment; however, the continuous slow release of 55Fe suggests that isotopic equilibrium will ultimately be attained.Our results imply a recrystallization of solid Fe(III) phases induced by the catalytic action of aqueous Fe(II). Accordingly, iron oxides should properly be considered as dynamic phases that change composition when exposed to variable redox conditions. These results necessitate a reevaluation of current models for the release of trace metals under reducing conditions, the sequestration of heavy metals by iron oxides, and the significance of stable iron isotope signatures.  相似文献   

16.
The forces of interaction were measured between the siderophore azotobactin and the minerals goethite (α-FeOOH) and diaspore (α-AlOOH) in aqueous solution using force microscopy. Azotobactin, a pyoverdin-type siderophore, was covalently linked to a hydrazide terminated atomic force microscope tip using a standard active ester protein coupling technique. Upon contact with each mineral surface, the adhesion force between azotobactin and goethite was two to three times the value observed for the isostructural Al-equivalent diaspore. The affinity for the solid iron oxide surface reflected in the force measurements correlates with the specificity of azotobactin for aqueous ferric iron. Further, the adhesion force between azotobactin and goethite significantly decreases (4 nN to 2 nN) when small amounts of soluble iron (0.1 μM FeCl3 · 6H2O) are added to the system at pH 3.5 suggesting a significant specific interaction between the chelating reactive center of azotobactin and the mineral surface. Changes in the force signature with pH and ionic strength were fairly predictable when considering mineral solubility, the charge character of the mineral surfaces, the molecular structure of azotobactin, and the intervening solution. For example, azotobactin-goethite adhesion values were consistently smaller at pH 3.5 relative to the forces at pH 7. At the lower pH, the large number of protons and the increase in the mineral solubility provides additional electron acceptors (e.g., H+ and Fe3+(aq)) that are free to compete for the basic oxygen chelating sites in the azotobactin structure. It is believed that this competition disrupts siderophore affinity for the surface resulting in decreased adhesion values.  相似文献   

17.
Smelting slags associated with base-metal vein deposits of the Sierra Almagrera area (SE Spain) show high concentrations of Ag (<5–180 ppm), As (12–750 ppm), Cu (45–183 ppm), Fe (3.2–29.8%), Pb (511–2150 ppm), Sb (22–620 ppm) and Zn (639–8600 ppm). The slags are mainly composed of quartz, fayalite, barite, melilite, celsian, pyrrhotite, magnetite, galena and Zn–Pb–Fe alloys. No glassy phases were detected. The following weathering-related secondary phases were found: jarosite–natrojarosite, cotunnite, cerussite, goethite, ferrihydrite, chalcanthite, copiapite, goslarite, halotrichite and szomolnokite. The weathering of slag dumps near the Mediterranean shoreline has contaminated the soils and groundwater, which has caused concentrations in groundwater to increase to 0.64 mg/L Cu, 40 mg/L Fe, 0.6 mg/L Mn, 7.6 mg/L Zn, 5.1 mg/L Pb and 19 μg/L As. The results of laboratory leach tests showed major solubilization of Al (0.89–12.6 mg/L), Cu (>2.0 mg/L), Fe (0.22–9.8 mg/L), Mn (0.85–40.2 mg/L), Ni (0.092–2.7 mg/L), Pb (>2.0 mg/L) and Zn (>2.5 mg/L), and mobilization of Ag (0.2–31 μg/L), As (5.2–31 μg/L), Cd (1.3–36.8 μg/L) and Hg (0.2–7 μg/L). The leachates were modeled using the numerical code PHREEQC. The results suggested the dissolution of fayalite, ferrihydrite, jarosite, pyrrhotite, goethite, anglesite, goslarite, chalcanthite and cotunnite. The presence of secondary phases in the slag dumps and contaminated soils may indicate the mobilization of metals and metalloids, and help to explain the sources of groundwater contamination.  相似文献   

18.
 Forty-three untreated and actively and passively (wetland) treated coal mine drainage sediments and five yellow-red pigments were characterized using X-ray fluorescence, fusion-inductively coupled plasma atomic emission spectroscopy, X-ray diffraction, and tristimulus colorimeter. Primary crystalline iron-bearing phases were goethite and lepidocrocite, and iron phases converted to hematite upon heating. Quartz was nearly ubiquitous except for synthetic pigments. Gypsum, bassinite, calcite, and ettringite were found in active treatment sediments. Iron concentrations from highest to lowest were synthetic pigment>wetland sediment>natural pigment>active treatment (untreated sediments varied more widely), and manganese was highest in actively treated sediments. Loss on ignition was highest for passively treated sediments. No clear trends were observed between quantified color parameters (L*, a*, b*, and Redness Index) and chemical compositions. Because sediments from passive treatment are similar in chemistry, mineralogy, and color to natural pigments, the mine drainage sediments may be an untapped resource for pigment. Received: 29 December 1997 · Accepted: 11 May 1998  相似文献   

19.
Numerous small deposits of U-rich laterites are found in the northwestern border of the Paraná Basin. Detailed mineralogy and chemistry of the uranium lateritic ores from the Iporá-Amorinopolis region were studied using classic petrographic techniques, X-ray diffraction and fluorescence, atomic absorption, infrared and Mössbauer spectrography, autoradiography, electron microprobe and scanning electron microscopy with energy-dispersive spectroscopy. The ore mineral assemblage is formed by goethite, lepidocrocite, hematite, quartz, calcedony, variscite, wavelite, apatite, collophane, barite, gypsite, renardite, meta-autunite I, uranophane, fourmarierite, koninchite, ranquilite, phospho-uranilite, meta-uranocircite I, meta-uranocircite II, metatyuyamunite, sklodowskite, parsonite and an hydrated Ca-silicate of uranium. The mineralization can be weakly disseminated in the laterite matrix with U probably adsorbed in the lepidocrocite; in pockets and impregnations of yellowish uranium phosphated within the laterite (U3O810%) and in nodules with U3O8 ranging from 25% to 55%. The nodules are the most common ore type, being typically concentric with a white porous barite-gypsite-apatite core, followed by a compact greenish-yellow rim with colloform uranophane and ranquilite, a yellow aggregate of meta-autunite I, renardite and koninchite and an outer brownish-yellow shell of goethite with disseminated fourmarierite, renardite and koninchite. Size, shape and chemistry of the nodules indicate replacement of brachiopods and chitinozoa that are abundant in the Ponta Grossa Fm. by a primary uraninite-pyrite assemblage that is found in drill cores from fresh rock. The U enrichment is accompanied by enrichment of Ba, Ca, Sr, Pb, Ce and Nd in sulphate, phosphate, hydrous silicate or vanadate phases. The efficient separation of metals like Ce and Nd in individual phases on the surface of barite illustrates a clear example of a natural chromatographic separation. Such a process may be an important mechanism to explain the varying microchemistry within a laterite profile where each successive microsystem represents a chromatographic column through which the solubilities of metals will vary slightly in the continuum of Eh- and pH-values.  相似文献   

20.
Discharge of Fe(II)-rich groundwaters into surface-waters results in the accumulation of Fe(III)-minerals in salinized sand-bed waterways of the Hunter Valley, Australia. The objective of this study was to characterise the mineralogy, micromorphology and pore-water geochemistry of these Fe(III) accumulations. Pore-waters had a circumneutral pH (6.2–7.2), were sub-oxic to oxic (Eh 59–453 mV), and had dissolved Fe(II) concentrations up to 81.6 mg L−1. X-ray diffraction (XRD) on natural and acid-ammonium-oxalate (AAO) extracted samples indicated a dominance of 2-line ferrihydrite in most samples, with lesser amounts of goethite, lepidocrocite, quartz, and alumino-silicate clays. The majority of Fe in the samples was bound in the AAO extractable fraction (FeOx) relative to the Na-dithionite extractable fraction (FeDi), with generally high FeOx:FeDi ratios (0.52–0.92). The presence of nano-crystalline 2-line ferrihydrite (Fe5HO3·4H2O) with lesser amounts of goethite (α-FeOOH) was confirmed by scanning electron microscopy (SEM) coupled with energy dispersive X-ray analysis (EDX), and transmission electron microscopy (TEM) coupled with selected area electron diffraction (SAED). In addition, it was found that lepidocrocite (γ-FeOOH), which occurred as nanoparticles as little as ∼5 lattice spacings thick perpendicular to the (0 2 0) lattice plane, was also present in the studied Fe(III) deposits. Overall, the results highlight the complex variability in the crystallinity and particle-size of Fe(III)-minerals which form via oxidation of Fe(II)-rich groundwaters in sand-bed streams. This variability may be attributed to: (1) divergent precipitation conditions influencing the Fe(II) oxidation rate and the associated supply and hydrolysis of the Fe(III) ion, (2) the effect of interfering compounds, and (3) the influence of bacteria, especially Leptothrix ochracea.  相似文献   

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