Amorphous Ferric Oxyhydroxide Research Articles

Factors controlling the distribution of transitional metal elements in marine hydrogenic ferromanganese crusts

A series of selective dissolution experiments were conducted on the hydrogenic ferromanganese crusts collected near Line Island to study the geochemistry of Mn, Fe, Cu, Co, Ni and Ti. Despite of the fact that the very close intergrowth between amorphous ferric oxyhydroxides and δ-MnO2 exists in the hydrogenic ferromanganese crusts, there is no isomorphous substitution between iron and manganese. This is because the two elements in oxides have different crystal chemistry and geochemistry, such assertion being in agreement with the results of selective dissolution experiments. Transitional metal elements such as Cu, Co, Ni and Ti are enriched in different phases, i.e. Ni and Co are incorporated into δ-MnO2 while Cu and Ti are incorporated into ferric oxyhydroxides. The distributions of the elements in amorphous ferric oxyhydroxides and δ-MnO2 are controlled by the existing states of the elements in the seawater and the crystal chemistry and geochemistry of these elements/ions in oxides.

Transformation dynamics and reactivity of dissolved and colloidal iron in coastal waters

We have investigated the chemical forms, reactivities and transformation kinetics of Fe(III) species present in coastal water with ion exchange and filtration methods. To simulate coastal water system, a mixture of ferric iron and fulvic acid was added to filtered seawater and incubated for a minute to a week. At each incubation time, the seawater sample was acidified with hydrochloric acid and then applied to anion exchange resin (AER) to separate negatively charged species (such as fulvic acid, its complexes with iron and iron oxyhydroxide coated with fulvic acid) from positively charged inorganic ferric iron (Fe(III)′). By monitoring the acid-induced Fe(III)′ over an hour, it was found that iron complexed by fulvic acid dissociated rapidly to a large extent (86–92% at pH 2), whereas amorphous ferric oxyhydroxide particles associated with fulvic acid (AFO-L) dissociated very slowly with the first-order dissociation rate constants ranging from 6.1 × 10 − 5 for pH 3 to 2.7 × 10 − 4 s − 1 for pH 2. Therefore, a brief acidification followed by the AER treatment (acidification/AER method) was likely to be able to determine fulvic acid complexes and thus differentiate the complexes from the AFO-L particles (the dissolution of AFO-L was insignificant during the brief acidification). The acidification/AER method coupled with a simple filtration technique suggested that the iron–fulvic acid complexes exist in both the < 0.02 μm and 0.02–0.45 μm size fractions in our coastal water system. The truly dissolved iron (< 0.02 μm) was relatively long-lived with a life-time of 14 days, probably due to the complexation by strong ligands. Such an acid-labile iron may be an important source of bioavailable iron in coastal environments, as a significant relationship between the chemical lability and bioavailability of iron has been well recognised.

Modelling retention of heavy metals in the Oostriku peat bog, Estonia: Comparison of predicted and observed results

Abstract In this study, the retention of Ca and other metals (Pb, Cu, Fe, Zn and Mn) in the Oostriku peat bog (central Estonia) was modelled. Equilibrium sorption of metals on amorphous ferric oxyhydroxide and solid organic matter was simulated at steady-state. Ferric oxyhydroxide formation and possible precipitation of other metals (Mn, Pb and Cu) in the peat was also assessed. Evolution of metal sorption fronts along a peat profile over time was simulated with a dynamic model to test if metal–metal competition effects could cause Pb and Cu to sorb at higher amounts in the uppermost peat than in the lower peat, as observed in the field. The predicted sorbed amounts of metals were compared with those previously observed in the peat. In general, good agreement between both batch and dynamic model results and the independent observations at the Oostriku peat site was obtained. This suggests that the relatively simple model approach employed here might be generally useful for assessing other peat sites and similar applications.

Copper isotope fractionation during its interaction with soil and aquatic microorganisms and metal oxy(hydr)oxides: Possible structural control

This work is aimed at quantifying the main environmental factors controlling isotope fractionation of Cu during its adsorption from aqueous solutions onto common organic (bacteria, algae) and inorganic (oxy(hydr)oxide) surfaces. Adsorption of Cu on aerobic rhizospheric ( Pseudomonas aureofaciens CNMN PsB-03) and phototrophic aquatic ( Rhodobacter sp. f-7bl, Gloeocapsa sp. f-6gl) bacteria, uptake of Cu by marine ( Skeletonema costatum) and freshwater ( Navicula minima, Achnanthidium minutissimum and Melosira varians) diatoms, and Cu adsorption onto goethite (FeOOH) and gibbsite (AlOOH) were studied using a batch reaction as a function of pH, copper concentration in solution and time of exposure. Stable isotopes of copper in selected filtrates were measured using Neptune multicollector ICP-MS. Irreversible incorporation of Cu in cultured diatom cells at pH 7.5–8.0 did not produce any isotopic shift between the cell and solution (Δ 65/63Cu(solid-solution)) within ±0.2‰. Accordingly, no systematic variation was observed during Cu adsorption on anoxygenic phototrophic bacteria ( Rhodobacter sp.), cyanobacteria ( Gloeocapsa sp.) or soil aerobic exopolysaccharide (EPS)-producing bacteria ( P. aureofaciens) in circumneutral pH (4–6.5) and various exposure times (3 min to 48 h): Δ 65Cu(solid-solution) = 0.0 ± 0.4‰. In contrast, when Cu was adsorbed at pH 1.8–3.5 on the cell surface of soil the bacterium P. aureofacienshaving abundant or poor EPS depending on medium composition, yielded a significant enrichment of the cell surface in the light isotope (Δ 65Cu (solid-solution) = −1.2 ± 0.5‰). Inorganic reactions of Cu adsorption at pH 4–6 produced the opposite isotopic offset: enrichment of the oxy(hydr)oxide surface in the heavy isotope with Δ 65Cu(solid-solution) equals 1.0 ± 0.25‰ and 0.78 ± 0.2‰ for gibbsite and goethite, respectively. The last result corroborates the recent works of Mathur et al. [Mathur R., Ruiz J., Titley S., Liermann L., Buss H. and Brantley S. (2005) Cu isotopic fractionation in the supergene environment with and without bacteria. Geochim. Cosmochim. Acta 69, 5233–5246] and Balistrieri et al. [Balistrieri L. S., Borrok D. M., Wanty R. B. and Ridley W. I. (2008) Fractionation of Cu and Zn isotopes during adsorption onto amorhous Fe(III) oxyhydroxide: experimental mixing of acid rock drainage and ambient river water. Geochim. Cosmochim. Acta 72, 311–328] who reported heavy Cu isotope enrichment onto amorphous ferric oxyhydroxide and on metal hydroxide precipitates on the external membranes of Fe-oxidizing bacteria, respectively. Although measured isotopic fractionation does not correlate with the relative thermodynamic stability of surface complexes, it can be related to their structures as found with available EXAFS data. Indeed, strong, bidentate, inner-sphere complexes presented by tetrahedrally coordinated Cu on metal oxide surfaces are likely to result in enrichment of the heavy isotope on the surface compared to aqueous solution. The outer-sphere, monodentate complex, which is likely to form between Cu 2+ and surface phosphoryl groups of bacteria in acidic solutions, has a higher number of neighbors and longer bond distances compared to inner-sphere bidentate complexes with carboxyl groups formed on bacterial and diatom surfaces in circumneutral solutions. As a result, in acidic solution, light isotopes become more enriched on bacterial surfaces (as opposed to the surrounding aqueous medium) than they do in neutral solution. Overall, the results of the present study demonstrate important isotopic fractionation of copper in both organic and inorganic systems and provide a firm basis for using Cu isotopes for tracing metal transport in earth-surface aquatic systems. It follows that both adsorption on oxides in a wide range of pH values and adsorption on bacteria in acidic solutions are capable of producing a significant (up to 2.5–3‰ (±0.1–0.15‰)) isotopic offset. At the same time, Cu interaction with common soil and aquatic bacteria, as well as marine and freshwater diatoms, at 4 < pH < 8 yields an isotopic shift of only ±0.2–0.3‰, which is not related to Cu concentration in solution, surface loading, the duration of the experiment, or the type of aquatic microorganisms.

Fractionation of Cu and Zn isotopes during adsorption onto amorphous Fe(III) oxyhydroxide: Experimental mixing of acid rock drainage and ambient river water

Fractionation of Cu and Zn isotopes during adsorption onto amorphous ferric oxyhydroxide is examined in experimental mixtures of metal-rich acid rock drainage and relatively pure river water and during batch adsorption experiments using synthetic ferrihydrite. A diverse set of Cu- and Zn-bearing solutions was examined, including natural waters, complex synthetic acid rock drainage, and simple NaNO3 electrolyte. Metal adsorption data are combined with isotopic measurements of dissolved Cu (65Cu/63Cu) and Zn (66Zn/64Zn) in each of the experiments. Fractionation of Cu and Zn isotopes occurs during adsorption of the metal onto amorphous ferric oxyhydroxide. The adsorption data are modeled successfully using the diffuse double layer model in PHREEQC. The isotopic data are best described by a closed system, equilibrium exchange model. The fractionation factors (αsoln–solid) are 0.99927±0.00008 for Cu and 0.99948±0.00004 for Zn or, alternately, the separation factors (Δsoln–solid) are −0.73±0.08‰ for Cu and −0.52±0.04‰ for Zn. These factors indicate that the heavier isotope preferentially adsorbs onto the oxyhydroxide surface, which is consistent with shorter metal–oxygen bonds and lower coordination number for the metal at the surface relative to the aqueous ion. Fractionation of Cu isotopes also is greater than that for Zn isotopes. Limited isotopic data for adsorption of Cu, Fe(II), and Zn onto amorphous ferric oxyhydroxide suggest that isotopic fractionation is related to the intrinsic equilibrium constants that define aqueous metal interactions with oxyhydroxide surface sites. Greater isotopic fractionation occurs with stronger metal binding by the oxyhydroxide with Cu>Zn>Fe(II).

Superoxide-Mediated Dissolution of Amorphous Ferric Oxyhydroxide in Seawater

We have investigated the kinetics of superoxide-mediated dissolution of amorphous ferric oxyhydroxide (AFO) in seawater by spectrophotometrically examining the rate of formation of a ferrous-ferrozine complex (Fe(II)(FZ)3) with particular attention given to the effect of aging and iron concentration on the rate of superoxide-mediated dissolution of AFO. The production rates of Fe(II)(FZ)3 decreased with aging of AFO for iron concentrations from 50 to 500 nM, indicating that changes to the chemical and physical properties of AFO affected the reactivity of inorganic ferric iron species with superoxide. A kinetic model developed by assuming that Fe(II)' formation is preceded by the thermal dissolution of AFO provided a good description of the Fe(II)(FZ)3 production rates over time. First-order rate constants for Fe(II)' formation were found to depend on the total iron concentration, suggesting that superoxide-mediated Fe(II) reduction is affected not only by the rate of thermal dissolution of AFO but also by the rate of AFO precipitation. The reported high rates of superoxide production by both photochemical and biotic pathways in aquatic systems coupled with the ability of superoxide to dissolve freshly formed ferric oxides suggest that this process may have a significant impact on the biogeochemical cycling of iron, especially if organisms have an affinity for ferrous iron.

Mineralogy and geochemistry of mill tailings impoundments from Algares (Aljustrel), Portugal: Implications for acid sulfate mine waters formation

Fine fractions from mill tailing deposits and filtrated material from acid mine waters were mineralogical and geochemical studied. Siderotil, copiapite, rhomboclase, natrojarosite, gypsum, amorphous ferric oxyhydroxide were identified by X-ray diffraction (XRD). Schwertmannite was identified by Infra-red spectroscopy (ATR-IR). Stretching modes of S–O bonds were analyzed either for finest fractions or filtrated material. The presence of SO 4 complexes identified either in bidentate or monodentate coordination affects the mobilization of bivalent metals (Me). Weak Me–SO 4 bond was found for filtrated phases from acid waters.

RETRACTED: Mechanical properties and corrosion resistance of low-alloy steels in atmospheric conditions containing chloride

The corrosion resistance (weight loss) and mechanical properties (i.e., yield strength, ultimate tensile strength, and elongation) of four newly developed low-alloy steels (LAS) were compared with a weathering steel (Acr-Ten A) and a carbon steel (SS400) using a laboratoryaccelerated test that involved cyclic wet/dry conditions in a chloride environment (5 wt.% NaCl). The new LAS were designated 1604A, 1604B, 1605A, and 1605B. After 72 cycles of cyclic corrosion tests, the change in mechanical properties by corrosion was the least for SS400, Acr-Ten A was second, and effects of corrosion on the mechanical properties of the other four low-alloy steels were similar. The susceptibility of the steels to corrosion based on their weight loss was the most for SS400, and the least for 1605A and 1605B. In addition, it was found that the corrosion potentials of low-alloy steels are more active prior to accelerated corrosion tests than after the accelerated test, and the corrosion tendency of the six steels immersed in 3.5 wt.% NaCl solutions after 72 cycles of accelerated corrosion tests was the least for 1605A and 1605B because the corrosion potentials were higher than other steels. The rust characteristics observed by SEM and analyzed by FTIR and EPMA indicated that most of the rust layers on the test steels were composed of a loose outer rust layer and a dense inner rust layer. The outer rust layer of each steel was composed of -FeOOH,-FeOOH, magnetite (Fe3O4), H2O, and amorphous ferric oxyhydroxide (FeOx(OH)3 − 2x, x = 0 to 1), while the inner rust layer was composed mainly of Fe3O4 with a little -FeOOH. In addition, it was apparent that the copper and chromium alloying additions were enriched, respectively, at the rust-layer/substrate interface and in the rust layers. Finally, combining the results of the accelerated tests, the rust layer analysis, and the corrosion potential measurements showed that low-alloy steels, such as 1605A and 1605B, have better weathering steel properties than Acr-Ten A for use in the humid and salty weather. © 2005 Elsevier B.V. All rights reserved.

Reduction of Organically Complexed Ferric Iron by Superoxide in a Simulated Natural Water

Superoxide (and potentially its conjugate acid hydroperoxyl) is unique among the reactive oxygen species in that its standard redox potential in circumneutral natural waters potentially allows it to reduce ferric iron to the more soluble ferrous state. Here we have observed the superoxide/ hydroperoxyl-mediated reduction of ferric complexes with a variety of synthetic organic ligands and several complexes with natural organic matter (NOM), as well as freshly precipitated amorphous ferric oxyhydroxide, in bicarbonate buffered solutions at pH 8.1. From measurements of superoxide decay in the presence of the complexes, we calculated second-order rate constants for superoxide/ hydroperoxyl-mediated reduction that vary from (9.3+/-0.2) x 10(3) M(-1) s(-1) for the complex between Fe(III) and desferrioxamine B up to (1.9+/-0.2) x 10(5) M(-1) s(-1) for Fe(III)-salicylate and (2.3+/-0.1) x 10(5) M(-1) s(-1) for one of the Fe(III)-NOM complexes. We also verified that ferrous iron was produced from superoxide/hydroperoxyl-mediated Fe(III) reduction using ferrozine to trap free Fe(II). Low yields of the ferrozine complex when compared to the measured rates of superoxide decay suggest that ferric complexes are reduced directlyto corresponding ferrous complexes, with much of the ferrous complex reoxidizing before it is able to release free ferrous iron. This is an important consideration for microorganisms, as the kinetics of trace metal uptake is typically governed by free ion activity.

Corrosion resistance and mechanical properties of low-alloy steels under atmospheric conditions

The corrosion resistance and mechanical strength of four newly developed low-alloy steels (LAS) were compared with a carbon steel (SS400) and a weathering steel (Acr-Ten A) using a laboratory-accelerated test that involved cyclic wet/dry conditions in a chloride environment (5 wt.% NaCl). The new LAS were designated 1605A, 1605B, 1604A, and 1604B. After 72 cycles of cyclic corrosion tests, the susceptibility of the steels to corrosion could be listed in the following order based on their weight loss (from high to low): SS400 > Acr-Ten A > 1604B ⩾ 1604A > 1605B ⩾ 1605A. The change in mechanical properties by corrosion was the least for SS400, Acr-Ten A was second, and effects of corrosion on the mechanical properties of the other four low-alloy steels were similar. Finally, the characteristics of the rust layers on each LAS sample were observed by SEM, and analyzed by FTIR and EPMA. The results indicated that most of the rust layers on the test steels were composed of a loose outer rust layer and a dense inner rust layer. The outer rust layer of each steel was composed of α-FeOOH, γ-FeOOH, magnetite (Fe 3O 4), H 2O, and amorphous ferric oxyhydroxide (FeO x (OH) 3−2 x , x=0–1), while the inner rust layer was composed mainly of Fe 3O 4 with a little α-FeOOH. In addition, it was apparent that the copper and chromium alloying additions were enriched, respectively, at the rust-layer/substrate interface and in the rust layers. Finally, combining the results of the accelerated tests and the rust layer analysis showed that low-alloy steels, such as 1605A and 1605B, have better weathering steel properties than Acr-Ten A for use in the humid and salty weather.

Effect of Fe(III) on 1,1,2,2-Tetrachloroethane Degradation and Vinyl Chloride Accumulation in Wetland Sediments of the Aberdeen Proving Ground

1,1,2,2-Tetrachloroethane (TeCA) contaminated groundwater at the Aberdeen Proving Ground discharges through an anaerobic wetland in West Branch Canal Creek (MD), where dechlorination occurs. Two microbially mediated pathways, dichloroelimination and hydrogenolysis, account for most of the TeCA degradation at this site. The dichloroelimination pathways lead to the formation of vinyl chloride (VC), a recalcitrant carcinogen of great concern. The goal of this investigation was to determine whether microbially-available Fe(III) in the wetland surface sediment influenced the fate of TeCA and its daughter products. Differences were identified in the TeCA degradation pathway between microcosms treated with amorphous ferric oxyhydroxide (AFO-treated) and untreated (no AFO) microcosms. TeCA degradation was accompanied by a lower accumulation of VC in AFO-treated microcosms than untreated microcosms. The microcosm incubations and subsequent experiments with the microcosm materials showed that AFO treatment resulted in lower production of VC by (1) shifting TeCA degradation from dichloroelimination pathways to production of a greater proportion of chlorinated ethane products, and (2) decreasing the microbial capability to produce VC from 1,2-dichloroethene (DCE). VC degradation was not stimulated in the presence of Fe(III). Rather, VC degradation occurred readily under methanogenic conditions and was inhibited under Fe(III)-reducing conditions.

Characterization of Fe(III) reduction by chlororespiring Anaeromyxobacter dehalogenans.

Anaeromyxobacter dehalogenans strain 2CP-C has been shown to grow by coupling the oxidation of acetate to the reduction of ortho-substituted halophenols, oxygen, nitrate, nitrite, or fumarate. In this study, strain 2CP-C was also found to grow by coupling Fe(III) reduction to the oxidation of acetate, making it one of the few isolates capable of growth by both metal reduction and chlororespiration. Doubling times for growth of 9.2 and 10.2 h were determined for Fe(III) and 2-chlorophenol reduction, respectively. These were determined by using the rate of [(14)C]acetate uptake into biomass. Fe(III) compounds used by strain 2CP-C include ferric citrate, ferric pyrophosphate, and amorphous ferric oxyhydroxide. The addition of the humic acid analog anthraquinone 2,6-disulfonate (AQDS) increased the reduction rate of amorphous ferric iron oxide, suggesting AQDS was used as an electron shuttle by strain 2CP-C. The addition of chloramphenicol to fumarate-grown cells did not inhibit Fe(III) reduction, indicating that the latter activity is constitutive. In contrast, the addition of chloramphenicol inhibited dechlorination activity, indicating that chlororespiration is inducible. The presence of insoluble Fe(III) oxyhydroxide did not significantly affect dechlorination, whereas the presence of soluble ferric pyrophosphate inhibited dechlorination. With its ability to respire chlorinated organic compounds and metals such as Fe(III), strain 2CP-C is a promising model organism for the study of the interaction of these potentially competing processes in contaminated environments.

Adsorption and Retention of U-238 and Th-232 from Groundwater Using BIOS

ABSTRACTBiofilms were grown in situ 296 metres below sea level in the Äspö Hard Rock Laboratory. The prominent organism in these biofilms wasGallionella ferruginea, which is an iron oxidising chemolithotrophic microorganism that grows in low oxygen conditions. This organism grows an organic stalk structure capable of binding and concentrating trace metals. This stalk structure also allows amorphous ferric iron oxyhydroxides, or BIOS, (bacteriogenic iron oxides) to precipitate. The pH of the groundwater within the system was between 7.4 and 7.6, with Eh potential between 150 and 190 mV and oxygen saturation between 3 and 15%. Biofilms developed within two weeks and were sampled every two weeks for three months. Cell number and stalk length was recorded for each sample. The concentration of Cr, Ni, Cu, Zn, Mo, REE (rare earth elements), U-238 and Th-232 was measured by ICP-MS. Early results suggested thatGallionellabiofilms and associated BIOS could potentially concentrate trace metals up to 1000 fold higher than levels within the host rock and over 1 000 000 times the levels in the groundwater over a period of years. These new experiments indicate thatGallionellabiofilms and BIOS can rapidly attenuate metals to levels over 1000 fold higher than the levels in the groundwater. This process can occur anywhere where reduced groundwater enters the waste repository tunnel, open cavities or where groundwater extrudes at the surface. Because of this, there is huge potential to use biofilms and BIOS for retention of radionuclides and pollution control.

Precipitation of acicular hydrogoethite (α-FeOOH·xH2O; 0.1 < x < 0.22) using morphology controlling cationic additives

Acicular hydrogoethite (α-FeOOH·xH2O; 0.1<x<0.22) particles of high aspect ratio of ≥10 and narrow size distribution with length ∼0.5μm are prepared by air oxidation of Fe(OH)2·xH2O (80<x<120) in presence of morphology controlling cationic additives (0.01at.% of Pd2+ or Rh3+). Growth of hydrogoethite particle proceeds by the oxidation of Fe(OH)2·xH2O to an intermediate phase through the nucleation within the amorphous ferric oxy-hydroxide [FeOx(OH)3−2x·yH2O] and growth of α-FeOOH·(H2O)x acicular particles with the aid of morphology controlling agents, as evidenced from X-ray diffraction (XRD) and transmission electron microscope (TEM) studies. Preferential adsorption of additives on certain crystallographic planes and thereby retarding the growth in the perpendicular direction, allows the particles to acquire acicular shape with high aspect ratio ∼10. Thermal analyses of hydrogoethite samples show excess weight loss (∼3–4%) compared to goethite samples. Presence of HOH vibrational absorptions arising from strongly coordinated water molecules in hydrogoethite and its absence in goethite is evidenced from IR spectra. H2O molecules in hydrogoethite are located in the strands of channel formed in between the double ribbons of FeO6 octahedra running parallel to c-axis of goethite, wherein the water molecules are bridging between the nearest neighbour cations.

Anaerobic biooxidation of Fe(II) by Dechlorosoma suillum.

Anaerobic microbial oxidation of Fe(II) was only recently discovered and very little is known about this metabolism. We recently demonstrated that several dissimilatory perchlorate-reducing bacteria could utilize Fe(II) as an electron donor under anaerobic conditions. Here we report on a more in-depth analysis of Fe(II) oxidation by one of these organisms, Dechlorosoma suillum. Similarly to most known nitrate-dependent Fe(II) oxidizers, D. suillum did not grow heterotrophically or lithoautotrophically by anaerobic Fe(II) oxidation. In the absence of a suitable organic carbon source, cells rapidly lysed even though nitrate-dependent Fe(II) oxidation was still occurring. The coupling of Fe(II) oxidation to a particular electron acceptor was dependent on the growth conditions of cells of D. suillum. As such, anaerobically grown cultures of D. suillum did not mediate Fe(II) oxidation with oxygen as the electron acceptor, while conversely, aerobically grown cultures did not mediate Fe(II) oxidation with nitrate as the electron acceptor. Anaerobic washed cell suspensions of D. suillum rapidly produced an orange/brown precipitate which X-ray diffraction analysis identified as amorphous ferric oxyhydroxide or ferrihydrite. This is similar to all other identified nitrate-dependent Fe(II) oxidizers but is in contrast to what is observed for growth cultures of D. suillum, which produced a mixed-valence Fe(II)-Fe(III) precipitate known as green rust. D. suillum rapidly oxidized the Fe(II) content of natural sediments. Although the form of ferrous iron in these sediments is unknown, it is probably a component of an insoluble mineral, as previous studies indicated that soluble Fe(II) is a relatively minor form of the total Fe(II) content of anoxic environments. The results of this study further enhance our knowledge of a poorly understood form of microbial metabolism and indicate that anaerobic Fe(II) oxidation by D. suillum is significantly different from previously described forms of nitrate-dependent microbial Fe(II) oxidation.

Anaerobic mineralization of toluene by enriched sediments with quinones and humus as terminal electron acceptors.

The anaerobic microbial oxidation of toluene to CO(2) coupled to humus respiration was demonstrated by use of enriched anaerobic sediments from the Amsterdam petroleum harbor (APH) and the Rhine River. Both highly purified soil humic acids (HPSHA) and the humic quinone moiety model compound anthraquinone-2,6-disulfonate (AQDS) were utilized as terminal electron acceptors. After 2 weeks of incubation, 50 and 85% of added uniformly labeled [(13)C]toluene were recovered as (13)CO(2) in HPSHA- and AQDS-supplemented APH sediment enrichment cultures, respectively; negligible recovery occurred in unsupplemented cultures. The conversion of [(13)C]toluene agreed with the high level of recovery of electrons as reduced humus or as anthrahydroquinone-2,6-disulfonate. APH sediment was also able to use nitrate and amorphous manganese dioxide as terminal electron acceptors to support the anaerobic biodegradation of toluene. The addition of substoichiometric amounts of humic acids to bioassay reaction mixtures containing amorphous ferric oxyhydroxide as a terminal electron acceptor led to more than 65% conversion of toluene (1 mM) after 11 weeks of incubation, a result which paralleled the partial recovery of electron equivalents as acid-extractable Fe(II). Negligible conversion of toluene and reduction of Fe(III) occurred in these bioassay reaction mixtures when humic acids were omitted. The present study provides clear quantitative evidence for the mineralization of an aromatic hydrocarbon by humus-respiring microorganisms. The results indicate that humic substances may significantly contribute to the intrinsic bioremediation of anaerobic sites contaminated with priority pollutants by serving as terminal electron acceptors.

磁性材料 ゲル熟成法により生成されたゲーサイト粒子の形態制御因子

α-FeOOH particles have been produced by the aging of amorphous ferric oxyhydroxide colloidal solution. The effects of addition of ions: OH-, Cl-, CO32-, PO43- and Co2+, on the process of formation and morphology of α-FeOOH particles have been clarified.(1) The mechanism of formation of α-FeOOH crystal particles is considered as the dissolution-recrystallization process. The formation reaction of a-FeOOH crystal particles from the amorphous ferric oxyhydroxide can be expressed by a rate equation of the first order reaction.(2) Since OH- and Cl- ions are selectively adsorptive to the side face parallel to c axis of α-FeOOH particles, the crystal growth of the side face is depressed.(3) Since CO32- ion is not selectively adsorptive to the specific crystal plane, but is adsorbed on each plane of the a, b and c crystal planes homogeneously, the crystal growth of those planes is depressed. The recrystallization process of Fe(OH)4- ion is shifted from the surface reaction control to the diffusion control with increasing CO32- and Cl- ion concentrations.(4) The asterisk type particles were produced in the limited narrow region of PO43- ion concentration. An asterisk type particle is heterogeneously junctioned particle of an α-Fe2O3 and several α-FeOOH crystals.

アモルファスオキシ水酸化鉄からの針状α‐ＦｅＯＯＨ粒子の生成に及ぼすコロイド母液のｐＨの影響

アモルファスオキシ水酸化鉄からの針状α‐ＦｅＯＯＨ粒子の生成に及ぼすコロイド母液のｐＨの影響

Depth distribution and chemical form of iron in low cross-linked crud-removing resin beds

Deep beds of low cross-linked ion-exchange resins have been tested as a means of corrosion-product removal from condensate water in boiling-water nuclear reactor (BWR) at Clinton Power Station, Illinois Power Company. The phase composition of iron deposits in two cores extracted at different times from the same used resin bed, and in particulate filters of influent and effluent water sampled prior to core extraction, were examined using Mössbauer spectroscopy. Deposits were predominantly magnetite, hematite, goethite and lepidocrocite. Although the distribution of iron showed a pronounced maximum near the top 10–20 cm of the bed with up to 15 mg Fe/cm 3, the percentage of different phases remained constant along the entire core length. Only a minor fraction of colloidal iron, consisting of ultrafine (∼3 nm) colloidal particles of amorphous ferric oxyhydroxide (ferrihydrite), was observed. These findings are significant, because the iron trapped on resins is commonly believed to represent soluble Fe 2+ species. Our results indicate that the primary mechanism of iron removal is by mechanical filtration of water-suspended particulates. Thus, the use of a deep bed condensate polisher as a filter produces an iron coating that inhibits cation exchanger performance; that particulate iron should be removed on a prefilter.

INFLUENCE OF IRON OXIDE FORMING CONDITIONS ON PYRITE OXIDATION

Iron released from pyrite during oxidation in slightly acid to alkaline conditions is known to produce one or more forms of iron oxide. There is, however, no solid understanding of how, and to what degree, these iron oxides affect pyrite oxidation. This was investigated by leaching pyrite in a chromatographic column with a 1-cm i.d. and a flow rate of 0.43 mL min-1 at room temperature with a solution containing hydrogen peroxide (H2O2) buffered with acetate. When the leaching solution reached pyrite surfaces, H2O2 oxidized a small portion of pyrite and released Fe3+. The latter hydrolyzed to form an amorphous ferric oxyhydroxide that precipitated as a passive coating on the pyritic surfaces. The rate of pyrite oxidation was shown to be suppressed greatly by these coatings. This suppressive effect was attributed first to the coating's ability to serve as a sink for Fe3+, thus making it no longer available to oxidize pyrite, and second to the coating's ability to act as a barrier to the upcoming H2O2, thereby physically protecting the pyritic surfaces. It was also shown that the above leaching solution acted as a coating agent when buffered at pH 4.0 to 6.0. Values higher than pH 6 were not investigated.