摘要 :
Iron (oxyhydr)oxides play important roles in the fixation of toxic elements and also in the distribution of nutrients for plants in soils. Aakaganeite and schwertmannite, as the iron oxyhydroxides having an analogous tunnel struct...
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Iron (oxyhydr)oxides play important roles in the fixation of toxic elements and also in the distribution of nutrients for plants in soils. Aakaganeite and schwertmannite, as the iron oxyhydroxides having an analogous tunnel structure, have been widely recognized in Fe-rich environments. The objective of this study was to examine the formation of akaganeite/ schwertmannite via biooxidation of 0.1 M of ferrous solution containing only Cl~-, SO_4~(2-) or both the anions with a Cl~-/SO_4~(2-) mole ratio of 1, 3, 6, and 10 by chloride-acclimated Acidithiobacillus ferrooxidans cells. Results showed that ferrous iron in chloride/sulfate-containing solutions could be easily biooxidized to ferric iron, and subsequent Fe(III)-hydrolysis/precipitation could result in the formation of large quantity of akaganeite/ schwertmannite precipitates. The resulting precipitates were identified to be the pure akaganeite (Fe_8O_8(OH)_(7.1)(Cl)_(0.9), the pure schwertmannite (Fe_8O_8(OH)_(4.42)(SO_4)_(1.79), and the main schwertmannite phase (Fe_8O_8(OH)_(8-2x)(SO_4)_x, with 1.09≤ x ≤1.73), respectively, under different Cl~-/SO_4~(2-) mole ratio conditions. Obviously, sulfate inhibited drastically the bioformation of akaganeite but facilitated schwertmannite phase occurrence in the ferrous solution containing both sulfate and chloride. However, the presence of chloride ion in initial ferrous solution containing sulfate and Acidithiobacillus ferrooxidans cells would affect the morphology and other characteristics of schwertmannite generated.
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摘要 :
In this study, a series of bath experiments were carried out to investigate the photoreduction of Cr(VI) by small molecular weight organic acids (SOAs) over jarosite, a mineral found in acid mine drainage (AMD). The results demons...
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In this study, a series of bath experiments were carried out to investigate the photoreduction of Cr(VI) by small molecular weight organic acids (SOAs) over jarosite, a mineral found in acid mine drainage (AMD). The results demonstrated that jarosite or SOAs alone was unable to effectively transform Cr(Vl) to Cr(III) even if exposed to an illumination of mimic solar light. However, an addition of jarosite significantly enhanced the reduction of Cr(VI) by SOAs under the same condition. The photocatalytic reduction of Cr(VI) was strongly influenced by pH, the initial concentrations and the structures of SOAs. Of the tested two SOAs, the reaction rates of photocatalytic reduction of Cr(VI) were in the order of oxalic acid > citric acid. The reaction obeyed to zero-order kinetics with respect to Cr(Vl) with excess SOAs. A possible mechanism for photoreduction of Cr(Vl) by SOAs over jarosite was proposed.
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摘要 :
Oxidation of FeSO_4 solution with initial pH in the range of 1.40-3.51 by Acidithiobacillus ferrooxidans LX5 cell at 26 ℃ and subsequent precipitation of resulting Fe(III) were investigated in the present study. Results showed th...
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Oxidation of FeSO_4 solution with initial pH in the range of 1.40-3.51 by Acidithiobacillus ferrooxidans LX5 cell at 26 ℃ and subsequent precipitation of resulting Fe(III) were investigated in the present study. Results showed that the oxidation rate of Fe(II) was around 1.2-3.9 mmol l~(-1) h~(-1). X-ray diffraction (XRD) indicated that the formed precipitates were composed of natrojarosite with schwertmannite when the initial pH was 3.51, while only schwertmannite was produced when initial pH was in the range of 1.60-3.44 and no precipitate occurred when initial pH≤1.40. Scanning electron microscope (SEM) analyses showed that precipitates formed in solution with initial pH 3.51 were spherical particles of about 0.4 μm in diameter and had a smooth surface, whereas precipitates in solution with initial pH≤3.44 were spherical particles of approximately 1.0 μm in diameter, having specific sea-urchin morphology. Specific surface area of the precipitates varied from 3.42 to 23.45 m~2 g~(-1). X-ray fluorescence analyses revealed that schwertmannite formed in solution with initial pH in the range of 2.00-3.44 had similar elemental composition and could be expressed as Fe_8O_8(OH)_(4.42)(SO_4)_(1.79), whereas Fe_8O_8(OH)_(4.36)(SO_4)_(1.82) and Fe_8O_8(OH)_(4.29)(SO_4)_(1.86) as its chemical formula when the initial pH was 1.80 and 1.60, respectively.
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