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Assessment of biogeochemical influence on metal sulfide and Fe (II) oxidation as inferred from oxygen, sulfur and Fe isotopes

Fe (II) ve sülfürlü minerallerin oksidasyonu sırasında biyojeokimyasal etkilerin oksijen, kükürt ve Fe izotopları tayin edilmesi

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  1. Tez No: 166654
  2. Yazar: NURGÜL ÇELİK BALCI
  3. Danışmanlar: DOÇ.DR. FUAT YAVUZ
  4. Tez Türü: Doktora
  5. Konular: Jeoloji Mühendisliği, Geological Engineering
  6. Anahtar Kelimeler: Belirtilmemiş.
  7. Yıl: 2005
  8. Dil: İngilizce
  9. Üniversite: İstanbul Teknik Üniversitesi
  10. Enstitü: Fen Bilimleri Enstitüsü
  11. Ana Bilim Dalı: Jeoloji Mühendisliği Ana Bilim Dalı
  12. Bilim Dalı: Belirtilmemiş.
  13. Sayfa Sayısı: 156

Özet

FE(II) VE SÜLFÖRLÜ MİNERALLERİN OKSİDASYONÜ SIRASINDA BİYOJEOKİMYASAL ETKİLERİN OKSİJEN, KÜKÜRT VE FE İZOTOPLARI İLE TAYİN EDİLMESİ ÖZET Bakterilerin katalize ettiği reaksiyonlar Fe, S, O ve C gibi birçok elementin jeokimyasal döngüsünde önemli yer alır. Sülfurlü minerallerinin oksitlenmesi; değişik jeokimyasal ortamlarda yaygın bir işlem olup O, S ve Fe minerallerinin döngüsünü kontrol eder. Ayrıca, sülfürlü minerallerinin oksidasyonu asit maden sahaları (AMS) olarak ta bilinen çeşitli çevre problemlerine yol açmaktadır. Bu tür sahaların yüksek metal içeriğine sahip olması ve ekolojik hayatı uzun süre etkilemesinden dolayı iyileştirilmesi kaçınılmazdır. Bu amaçla, sülfürlü minerallerinin oksidasyon mekanizmalarının ortaya konması gerekir. Sülfürlü minerallerin bakteriler tarafından oksitlendiği yaygın bir şekilde kabul edilmektedir. Sülfür ve Fe (II) oksitleyen A. Ferrooxidans bakteri türü, asit maden sahalarında yaygın olarak bulunmaktadır. Bu nedenle, sülfürlü minerallerinin oksidasyon mekanizmasının ve bakterilerin buna katkısının ortaya konması güncel ve eski ortamlarda sülfür ve oksijen döngüsünün anlaşılmasına ve aynı zamanda da asit maden sahalarının iyileştirilmesi için alınacak tedbirlerin belirlenmesine yardımcı olacaktır. Bu çalışmada, bakteriyel reaksiyonların asit koşullar (pH

Özet (Çeviri)

ASSESSMENT OF BIOGEOCHEMICAL INFLUENCE ON METAL SULFIDE AND FE (H) OXIDATION AS INFERRED FROM OXYGEN, SULFUR AND FE ISOTOPES SUMMARY Bacterially catalyzed reactions are important in geochemical cycling of large variety elements such as Fe, S, O and C. Sulfide mineral oxidation is widespread in many different environments and also regulates the global cycling of O, S and Fe. Furifcrmore, oxidation of metal sulfide minerals cause environmental problems known as acid mine drainage (AMD). Since AMD environments contain high concentration of metals and affect aquatic ecosystems, remediation of these environments is vital and requires an understanding of oxidation mechanism of sulfide minerals. It is widely accepted that oxidation of sulfide minerals is often mediated by bacterial reactions. The Fe(H) and sulfide oxidizing bacterium, Acidithiobacillus ferrooxidans, is commonly found in AMD sites. Understanding the mechanism and bacterial contribution to metal sulfide oxidation may assist with developing proper remediation strategies for AMD sites and contribute to our understanding of sulfur and oxygen cycle in ancient and modern environments. My «doctoral studies examined the bacterial influence on the oxidation of sulfide minerals at pH and -29.7 %o for the biotic and abiotic experiments, respectively. The similarity between biotic and abiotic experiments may indicate the same oxidation mechanisms for pyrite. Data from aerobic pyrite experiments indicated that Fe (III) ions were the main oxidizing agent during pyrite oxidation and the role of bacteria was mainly to oxidize Fe (II) to Fe(ffl). The 8I8Oso4 values from the anaerobic pyrite experiments show 100 % water oxygen in both biotic and abiotic experiments, indicating that chemical oxidation of pyrite by Fe (111) was dominant in both experiments. Kinetic oxygen isotope fractionation effect between sulfate and water (A Oso4-rezo) was estimated to be 4.2 %> and 3.5%o for the biotic and abiotic experiments, respectively. It is interesting that kinetic oxygen isotope fractionation between sulfate and water (A18Oso4-H2o) from the anaerobic experiments is similar to that from the aerobic long term pyrite experiments. The 534Sso4 values from aerobic experiments closely reflect the 534S composition of pyrite during both biotic and abiotic experiments in contrast to the anaerobic experiments which show -1 %o fractionation relative to the S34SFeS2 values during both biotic and abiotic oxidation. Chapter 3: Aerobic and Anaerobic Bacterial and abiotic ZnS and 12 % Fe-bearing Sphalerite Experiments The Sî8Oso4 values from both aerobic biological ZnS and Fe-containing sphalerite experiments indicated that all oxygen atoms in sulfate are derived from water during the short and long term experiments. In contrast to biological experiments, 8180so4 values from abiotic ZnŞ experiments confirmed that a significant fraction of the oxygen in sulfate is derived from molecular oxygen (60 %). Differences in the percentage of molecular oxygen incorporated into sulfate between the biological and the abiotic experiments may imply different oxidation mechanism for each. The 100 % of water-oxygen into sulfate produced during biological experiments is in agreement with the theoretical sulfide oxidation pathway proposed by Kelly (1 982). My experimental results showed that although the proposed pathway may explain the overall mass transformation during sphalerite oxidation, it does not explain the actual oxygen source to sulfate. The net stoichiometry of the proposed pathway suggests 100 % molecular oxygen incorporation into sulfate (reaction 16, chapter 3). Xll1 R Oxygen isotope fractionation effect between sulfate and water (A Oscw-mo) was estimated to be 9 %o for both short and long term pure sphalerite experiments and 8.2 and 12 %> for the short and long term Fe-bearing sphalerite experiments, respectively. Analogous between oxygen isotope fractionation effects during ZnS and Fe-bearing sphalerite oxidation may indicate the same reaction mechanism for each. Furthermore, the similar 818Oso4 values between ZnS and Fe-bearing sphalerite experiments suggest that Fe (II) in the crystal lattice of sphalerite mineral have no effect on the 6I80So4 values unless it is overprinted by other processes such as oxygen isotope exchange between water and sulfite. Aerobic bacterial and abiotic elemental sulfur experiments The 5I8Oso4 values produced from the biological elemental sulfur oxidation showed 100 % water-oxygen incorporation into sulfate as in sphalerite experiments. Oxygen isotope fractionation effect (A,8Oso4-h2o) was estimated to be 8 %o and 8.9 %o for the short and long term experiments, respectively. The 8I8Oso4 values and the oxygen isotope fractionation effect from elemental sulfur experiments are very similar to those from aerobic sphalerite experiments. These results may indicate that elemental sulfur is the main sulfur intermediate during sphalerite oxidation (reaction 14) and subsequent oxidation is controlled by biological reactions since abiotic elemental sulfur experiments did not produce significant amount sulfate over the period of experiments. Consequently, these experimental results suggest mat the actual sulfur moiety of sphalerite oxidized to sulfate is likely elemental sulfur. This explains why the 5I8Oso4 values from sphalerite experiments are almost identical to the 818Oso4 values from elemental sulfur experiments. These determinations are also consistent with the 834Sso4 values from anaerobic sphalerite experiments. The sulfur isotope composition of elemental sulfur extracted from sphalerite surface at the end of the anaerobic oxidation experiments is identical to source of sphalerite, indicating that most of the sulfur moiety of sphalerite is oxidized to elemental sulfur under anaerobic conditions as well (reaction 1 8) and minor amount sulfate form. Although the 818Oso4 values from ZnS and Fe-bearing sphalerite experiments are very similar under both aerobic and anaerobic conditions, these values are different from the 818Oso4 values produced during aerobic and anaerobic pyrite oxidation experiments. Oxygen isotope fractionation effect (A180so4-H2o) is also different for pyrite and sphalerite experiments. -9 %o oxygen isotope fractionation effect between water and sulfate seems to be unique to sphalerite oxidation experiments since the same fractionation effect is ~ 4 %o for pyrite experiments. Therefore, oxygen isotope fractionation effect between water and sulfate may be used to reveal the source of sulfide minerals. Chapter 4: Iron isotope fractionation during microbiaîly-stimulated Fe[II] oxidation and Fe[III] precipitation Interpretation of the origins of iron-bearing minerals preserved in modern and ancient rocks based on measured 56Fe/54Fe ratios depends on our ability to distinguish between biological and non-biological iron isotope fractionation xmprocesses. In this study, we compared ^e/^Fe ratios of coexisting aqueous iron (FejTTjaq, Fe[ni]aq) and iron oxyhydroxide precipitates (FePITjppt) resulting from the oxidation of ferrous iron under experimental conditions at low pH (

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