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ABSTRACT: Iron-bacteria composite suspensions were prepared by exposure of Anoxybacillus flavithermus cells to increasing concentrations of Fe2+ cations under different degrees of oxidation. Cd2+ immobilization was investigated during and after the synthesis of the iron-bacteria composites via scanning electron microscopy and isotherm sorption experiments conducted at varied ratios of total iron to bacteria (expressed by the variable ρ, mg Fe per g dry bacteria). At ρ less than about 20, precipitation of Fe(III) oxide was hindered, and for ρ up to about 50 Cd immobilization was decreased relative to iron-free control experiments, even for conditions where Fe(III) oxide was forming. For ρ above 50 to the maximum investigated value of 124, the Cd immobilization capacity of the iron-bacteria composite suspensions was partly recovered. Surface complexation models developed to describe the data indicate that 1) Fe2+ and Cd2+ cations compete with comparable affinities for the reactive sites on the bacterial cell walls, and 2) sorption of the progressively oxidizing iron can reduce the total concentration of bacterial surface sites available for metal adsorption by more than 40%, inferred to be due to masking or blocking of the binding sites by Fe(II) or Fe(III) monomers or oligomers or precipitated Fe(III) oxides. This study demonstrates that the immobilization of metal cations in bacteria-bearing settings cannot be examined independently of redox processes such as the oxidation, hydrolysis and precipitation of iron.
Geomicrobiology 01/2011; 28(1):11-22. · 2.02 Impact Factor
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ABSTRACT: Bacteria are known to associate closely with secondary iron oxides in natural environments, but it is still unclear whether they catalyze their precipitation. Here, Fe2+ ions were progressively added to various concentrations of Bacillus subtilis bacteria in permanently oxic conditions while maintaining the pH at 6.5 by adding a NaOH solution at a monitored rate. The iron/ bacteria precipitates were characterized by wet chemistry, SEM, and XRD. Abiotic syntheses produced nanolepidocrocite, and their kinetics displayed a strong autocatalytic effect. Biotic syntheses led to the formation of tiny and poorly crystallized particles at intermediate bacterial concentrations and to a complete inhibition of particle formation at high bacterial concentrations. The occurrence of the autocatalytic effect was delayed and its intensity was reduced. Both the oxidation and the hydrolysis of Fe2+ ions were hindered.
Environmental Science and Technology 05/2008; 42(9):3194-200. · 5.23 Impact Factor
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10th European Meeting on Environmental Chemistry.
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Geophysical Reseach Abstracts.
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ABSTRACT: The aim of this study was to design and test a new tool for (i) the quantitative in situ monitoring of Fe(III) reduction in soils and (ii) the tracking of the potential mineralogical changes of Fe-oxides. The tool consists of small (2 × 2 × 0.2 cm) striated polymer plates coated with synthetic pure ferrihydrite or As-doped ferrihydrite (Fh–As). These slides were then inserted within two different horizons (organo-mineral and albic) located in a wetland soil with alternating redox conditions. Dissolution was quantified by X-ray fluorescence (XRF) analyses of total metal contents before and after insertion into the soil. The crystallographic evolution of Fe-oxides was characterized by scanning electron microscope equipped with an energy-dispersive spectrometer (SEM–EDS). Over the months, the ferrihydrite progressively disappeared, at rates comparable to those previously measured in laboratory studies, i.e. in the 1–10 × 10−12 mol Fe m−2 s−1 range. SEM observations indicate that the supports were highly colonized by bacteria and biofilms in the organo-mineral horizon, suggesting a biological-mediated process, while the albic horizon appeared to be characterized by a mostly chemical-mediated process. In the albic horizon, Fe-sulphide and other micro-precipitates were formed after 7 months of incubation in balance with a quasi dissolution of initial Fe-oxides.
Applied Geochemistry.
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ABSTRACT: Polymer slides covered by synthetic As-spiked ferrihydrite (As-Fh) or As-spiked lepidocrocite (As-Lp) were inserted into an organic-rich wetland soil in non conventional columns system under anaerobic conditions. Slides were recovered after different periods of time to evaluate (i) the impact of (bio)reduction on both Fe-oxide dissolution and secondary mineral precipitation and, (ii) the subsequent effects on As mobility. The calculated Fe dissolution rates for As-Fh and As-Lp were 2.02 · 10− 9 and 1.92 · 10− 9 mol Fe m− 2 s− 1, respectively, and were higher than what has been commonly reported in laboratory studies. Important bacterial colonization and occurrence of biofilm suggest the presence of biologically mediated processes. The newly formed minerals were mostly composed of Fe-sulphides. Fe(II) complexation by organic molecules in solution likely prevented formation of secondary Fe(II, III)-rich minerals. The relative proportion of As(III) increased with time on the As-Fh slides, and was combined with a decrease of the Fe/As ratio, suggesting a partial adsorption of As(III) onto minerals. By contrast, for lepidocrocite, the Fe/As ratio increased, suggesting that As(III) was less readsorbed due the lower available site number and the deletion of As adsorption sites on the reduced lepidocrocite surface. Reduction and subsequent As sequestration appeared to result from a coupled biotic–abiotic reaction pathway in which Fe or As reducing-bacteria allowed the reduction of As(V) to As(III).
Chemical Geology.
