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Oxygen and sulfur isotope systematics of sulfate produced by bacterial and abiotic oxidation of pyrite 总被引：4，自引：0，他引：4
Nurgul Balci Wayne C. Shanks III Kevin W. Mandernack 《Geochimica et cosmochimica acta》2007,71(15):3796-3811
To better understand reaction pathways of pyrite oxidation and biogeochemical controls on δ18O and δ34S values of the generated sulfate in acid mine drainage (AMD) and other natural environments, we conducted a series of pyrite oxidation experiments in the laboratory. Our biological and abiotic experiments were conducted under aerobic conditions by using O2 as an oxidizing agent and under anaerobic conditions by using dissolved Fe(III)aq as an oxidant with varying δ18OH2O values in the presence and absence of Acidithiobacillus ferrooxidans. In addition, aerobic biological experiments were designed as short- and long-term experiments where the final pH was controlled at ∼2.7 and 2.2, respectively. Due to the slower kinetics of abiotic sulfide oxidation, the aerobic abiotic experiments were only conducted as long term with a final pH of ∼2.7. The δ34SSO4 values from both the biological and abiotic anaerobic experiments indicated a small but significant sulfur isotope fractionation (∼−0.7‰) in contrast to no significant fractionation observed from any of the aerobic experiments. Relative percentages of the incorporation of water-derived oxygen and dissolved oxygen (O2) to sulfate were estimated, in addition to the oxygen isotope fractionation between sulfate and water, and dissolved oxygen. As expected, during the biological and abiotic anaerobic experiments all of the sulfate oxygen was derived from water. The percentage incorporation of water-derived oxygen into sulfate during the oxidation experiments by O2 varied with longer incubation and lower pH, but not due to the presence or absence of bacteria. These percentages were estimated as 85%, 92% and 87% from the short-term biological, long-term biological and abiotic control experiments, respectively. An oxygen isotope fractionation effect between sulfate and water (ε18OSO4-H2O) of ∼3.5‰ was determined for the anaerobic (biological and abiotic) experiments. This measured value was then used to estimate the oxygen isotope fractionation effects between sulfate and dissolved oxygen in the aerobic experiments which were −10.0‰, −10.8‰, and −9.8‰ for the short-term biological, long-term biological and abiotic control experiments, respectively. Based on the similarity between δ18OSO4 values in the biological and abiotic experiments, it is suggested that δ18OSO4 values cannot be used to distinguish biological and abiotic mechanisms of pyrite oxidation. The results presented here suggest that Fe(III)aq is the primary oxidant for pyrite at pH < 3, even in the presence of dissolved oxygen, and that the main oxygen source of sulfate is water-oxygen under both aerobic and anaerobic conditions. 相似文献
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Nurgul Celik Balci 《Environmental Earth Sciences》2010,60(3):485-493
A series of experiments was conducted to better understand the bacterial influence on the release of trace metals during oxidation
of sphalerite mineral and element cycles in acid mine drainage (AMD) systems. Batch experiments were carried out as biotic
and abiotic control at pH 3. Acidithiobacillus ferrooxidans, sulfur and Fe(II) oxidizer, was used in the biotic sphalerite experiment. The abiotic control experiment was run without
adding the bacteria. The release behavior of six trace metals (As, Cd, Co, Pb, Cu and Mn), Fe and Zn were determined during
the period of 54 days. Compared to the abiotic experiments, enhanced oxidation of sphalerite by bacteria produced high sulfate
(~2,000 mg/L) and Fetot (139 mg/L) along with the low pH (<2.3). Consistent with this, the concentration of trace metals (As, Cd, Co, Pb, Cu and
Mn) was significantly higher in the biotic experiments than those in the abiotic experiments. Results indicate that the distributions
of Co and Cd in both biotic and abiotic experiments are directly related to the sphalerite dissolution whereas Pb, Cu distribution
shows no strong relation to sphalerite dissolution especially in the abiotic experiments. Pb distribution in the solution
appears to be controlled by pH-dependent solubility. Approximately 80% of the trace metals were removed from the solution
at the end of the biotic experiments along with biologically induced Fe precipitation. Experimental results showed that bacteria
play major role not only in the release of trace metal from sphalerite but also in controlling concentration of the metals
in the solution by producing Fe-oxyhydroxides. The study suggest that in order to develop an effective rehabilitation strategy
for AMD, it is necessary to understand bio/geochemical processes governing mobilization and deposition of trace metals in
the environment. 相似文献
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Determination of spatial distribution of coal quality parameters can ease management of the operations in coal mines. In this study, in order to provide guidance for the excavations, Can coal mine production map showing regions having suitable coal parameters as feed coals for a power plant and also for public sale was prepared using adaptive neuro-fuzzy inference system tool. Statistical relationships among calorific value, ash content and sulphur content were evaluated using the data obtained from boreholes opened in the mine between 2006 and 2009. According to the obtained production map, coals of Can mine are not suitable for public sale because of their high sulphur content and hence they should be blended with low sulphur coals to meet the requirements, before sale. 相似文献
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Iron isotope fractionation during microbially stimulated Fe(II) oxidation and Fe(III) precipitation 总被引：4，自引：0，他引：4
Nurgul Balci Thomas D. Bullen Wayne C. Shanks Kevin W. Mandernack 《Geochimica et cosmochimica acta》2006,70(3):622-639
Interpretation of the origins of iron-bearing minerals preserved in modern and ancient rocks based on measured iron isotope ratios depends on our ability to distinguish between biological and non-biological iron isotope fractionation processes. In this study, we compared 56Fe/54Fe ratios of coexisting aqueous iron (Fe(II)aq, Fe(III)aq) and iron oxyhydroxide precipitates (Fe(III)ppt) resulting from the oxidation of ferrous iron under experimental conditions at low pH (<3). Experiments were carried out using both pure cultures of Acidothiobacillus ferrooxidans and sterile controls to assess possible biological overprinting of non-biological fractionation, and both SO42− and Cl− salts as Fe(II) sources to determine possible ionic/speciation effects that may be associated with oxidation/precipitation reactions. In addition, a series of ferric iron precipitation experiments were performed at pH ranging from 1.9 to 3.5 to determine if different precipitation rates cause differences in the isotopic composition of the iron oxyhydroxides. During microbially stimulated Fe(II) oxidation in both the sulfate and chloride systems, 56Fe/54Fe ratios of residual Fe(II)aq sampled in a time series evolved along an apparent Rayleigh trend characterized by a fractionation factor αFe(III)aq-Fe(II)aq ∼ 1.0022. This fractionation factor was significantly less than that measured in our sterile control experiments (∼1.0034) and that predicted for isotopic equilibrium between Fe(II)aq and Fe(III)aq (∼1.0029), and thus might be interpreted to reflect a biological isotope effect. However, in our biological experiments the measured difference in 56Fe/54Fe ratios between Fe(III)aq, isolated as a solid by the addition of NaOH to the final solution at each time point under N2-atmosphere, and Fe(II)aq was in most cases and on average close to 2.9‰ (αFe(III)aq-Fe(II)aq ∼ 1.0029), consistent with isotopic equilibrium between Fe(II)aq and Fe(III)aq. The ferric iron precipitation experiments revealed that 56Fe/54Fe ratios of Fe(III)aq were generally equal to or greater than those of Fe(III)ppt, and isotopic fractionation between these phases decreased with increasing precipitation rate and decreasing grain size. Considered together, the data confirm that the iron isotope variations observed in our microbial experiments are primarily controlled by non-biological equilibrium and kinetic factors, a result that aids our ability to interpret present-day iron cycling processes but further complicates our ability to use iron isotopes alone to identify biological processing in the rock record. 相似文献
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