B. Mayer
W. C. Pat Shanks III
K.W. Mandernack
N. Balci
2012
<p><span>Studies of metal sulfide oxidation in acid mine drainage (AMD) systems have primarily focused on pyrite oxidation, although acid soluble sulfides (e.g., ZnS) are predominantly responsible for the release of toxic metals. We conducted a series of biological and abiotic laboratory oxidation experiments with pure and Fe-bearing sphalerite (ZnS & Zn</span><sub>0.88</sub><span>Fe</span><sub>0.12</sub><span>S), respectively, in order to better understand the effects of sulfide mineralogy and associated biogeochemical controls of oxidation on the resultant δ</span><sup>34</sup><span>S and δ</span><sup>18</sup><span>O values of the sulfate produced. The minerals were incubated in the presence and absence of </span><i>Acidithiobacillus ferrooxidans</i><span> at an initial solution pH of 3 and with water of varying δ</span><sup>18</sup><span>O values to determine the relative contributions of H</span><sub>2</sub><span>O-derived and O</span><sub>2</sub><span>-derived oxygen in the newly formed sulfate. . Experiments were conducted under aerobic and anaerobic conditions using O</span><sub>2</sub><span> and Fe(III)</span><sub>aq</sub><span> as the oxidants, respectively. Aerobic incubations with </span><i>A. ferrooxidans</i><span>, and S</span><sup>o</sup><span> as the sole energy source were also conducted. The </span><span class="math"><span id="MathJax-Element-1-Frame" class="MathJax_SVG" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mrow is="true"><mi mathvariant="normal" is="true">&#x3B4;</mi><msup is="true"><mrow is="true" /><mrow is="true"><mn is="true">34</mn></mrow></msup><msub is="true"><mrow is="true"><mtext is="true">S</mtext></mrow><mrow is="true"><msub is="true"><mrow is="true"><mtext is="true">SO</mtext></mrow><mrow is="true"><mn is="true">4</mn></mrow></msub></mrow></msub></mrow></math>"><span class="MJX_Assistive_MathML">δ34SSO4</span></span></span><span> values from both the biological and abiotic oxidation of ZnS and ZnS</span><sub>Fe</sub><span> by Fe(III)</span><sub>aq</sub><span> produced sulfur isotope fractionations (</span><span class="math"><span id="MathJax-Element-2-Frame" class="MathJax_SVG" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mrow is="true"><mi mathvariant="normal" is="true">&#x3B5;</mi><msup is="true"><mrow is="true" /><mrow is="true"><mn is="true">34</mn></mrow></msup><msub is="true"><mrow is="true"><mtext is="true">S</mtext></mrow><mrow is="true"><msub is="true"><mrow is="true"><mtext is="true">SO</mtext></mrow><mrow is="true"><mn is="true">4</mn></mrow></msub><mo is="true">-</mo><mtext is="true">ZnS</mtext></mrow></msub></mrow></math>"><span class="MJX_Assistive_MathML">ε34SSO4-ZnS</span></span></span><span>) of up to −2.6‰, suggesting the accumulation of sulfur intermediates during incomplete oxidation of the sulfide. No significant sulfur isotope fractionation was observed from any of the aerobic experiments. Negative sulfur isotope enrichment factors (</span><span class="math"><span id="MathJax-Element-3-Frame" class="MathJax_SVG" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mrow is="true"><mi mathvariant="normal" is="true">&#x3B5;</mi><msup is="true"><mrow is="true" /><mrow is="true"><mn is="true">34</mn></mrow></msup><msub is="true"><mrow is="true"><mtext is="true">S</mtext></mrow><mrow is="true"><msub is="true"><mrow is="true"><mtext is="true">SO</mtext></mrow><mrow is="true"><mn is="true">4</mn></mrow></msub><mo is="true">-</mo><mtext is="true">ZnS</mtext></mrow></msub></mrow></math>"><span class="MJX_Assistive_MathML">ε34SSO4-ZnS</span></span></span><span>) in AMD systems could reflect anaerobic, rather than aerobic pathways of oxidation. During the biological and abiotic oxidation of ZnS and ZnS</span><sub>Fe</sub><span> by Fe(III)</span><sub>aq</sub><span> all of the sulfate oxygen was derived from water, with measured </span><span class="math"><span id="MathJax-Element-4-Frame" class="MathJax_SVG" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mrow is="true"><mi mathvariant="normal" is="true">&#x3B5;</mi><msup is="true"><mrow is="true" /><mrow is="true"><mn is="true">18</mn></mrow></msup><msub is="true"><mrow is="true"><mtext is="true">O</mtext></mrow><mrow is="true"><msub is="true"><mrow is="true"><mtext is="true">SO</mtext></mrow><mrow is="true"><mn is="true">4</mn></mrow></msub><mo is="true">-</mo><msub is="true"><mrow is="true"><mtext is="true">H</mtext></mrow><mrow is="true"><mn is="true">2</mn></mrow></msub><mtext is="true">O</mtext></mrow></msub></mrow></math>"><span class="MJX_Assistive_MathML">ε18OSO4-H2O</span></span></span><span> values of 8.2</span><span> </span><span>±</span><span> </span><span>0.2‰ and 7.5</span><span> </span><span>±</span><span> </span><span>0.1‰, respectively. Also, during the aerobic oxidation of ZnS</span><sub>Fe</sub><span> and S</span><sup>o</sup><span> by </span><i>A</i><span>. </span><i>ferrooxidans</i><span>, all of the sulfate oxygen was derived from water with similar measured </span><span class="math"><span id="MathJax-Element-5-Frame" class="MathJax_SVG" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mrow is="true"><mi mathvariant="normal" is="true">&#x3B5;</mi><msup is="true"><mrow is="true" /><mrow is="true"><mn is="true">18</mn></mrow></msup><msub is="true"><mrow is="true"><mtext is="true">O</mtext></mrow><mrow is="true"><msub is="true"><mrow is="true"><mtext is="true">SO</mtext></mrow><mrow is="true"><mn is="true">4</mn></mrow></msub><mo is="true">-</mo><msub is="true"><mrow is="true"><mtext is="true">H</mtext></mrow><mrow is="true"><mn is="true">2</mn></mrow></msub><mtext is="true">O</mtext></mrow></msub></mrow></math>"><span class="MJX_Assistive_MathML">ε18OSO4-H2O</span></span></span><span> values of 8.1</span><span> </span><span>±</span><span> </span><span>0.1‰ and 8.3</span><span> </span><span>±</span><span> </span><span>0.3‰, respectively. During biological oxidation of ZnS by O</span><sub>2</sub><span>, an estimated 8% of sulfate–oxygen was derived from O</span><sub>2</sub><span>, which is enriched in </span><sup>18</sup><span>O relative to water, thus resulting in a larger apparent </span><span class="math"><span id="MathJax-Element-6-Frame" class="MathJax_SVG" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mrow is="true"><mi mathvariant="normal" is="true">&#x3B5;</mi><msup is="true"><mrow is="true" /><mrow is="true"><mn is="true">18</mn></mrow></msup><msub is="true"><mrow is="true"><mtext is="true">O</mtext></mrow><mrow is="true"><msub is="true"><mrow is="true"><mtext is="true">SO</mtext></mrow><mrow is="true"><mn is="true">4</mn></mrow></msub><mo is="true">-</mo><msub is="true"><mrow is="true"><mtext is="true">H</mtext></mrow><mrow is="true"><mn is="true">2</mn></mrow></msub><mtext is="true">O</mtext></mrow></msub></mrow></math>"><span class="MJX_Assistive_MathML">ε18OSO4-H2O</span></span></span><span> value of 9.5‰. Based on the data presented we hypothesize that the similar </span><span class="math"><span id="MathJax-Element-7-Frame" class="MathJax_SVG" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mrow is="true"><mi mathvariant="normal" is="true">&#x3B5;</mi><msup is="true"><mrow is="true" /><mrow is="true"><mn is="true">18</mn></mrow></msup><msub is="true"><mrow is="true"><mtext is="true">O</mtext></mrow><mrow is="true"><msub is="true"><mrow is="true"><mtext is="true">SO</mtext></mrow><mrow is="true"><mn is="true">4</mn></mrow></msub><mo is="true">-</mo><msub is="true"><mrow is="true"><mtext is="true">H</mtext></mrow><mrow is="true"><mn is="true">2</mn></mrow></msub><mtext is="true">O</mtext></mrow></msub></mrow></math>"><span class="MJX_Assistive_MathML">ε18OSO4-H2O</span></span></span><span> values of ∼8‰ from all of the aerobic and anaerobic experiments result from a common rate-limiting step that involves oxygen isotopic exchange between a sulfite (</span><span class="math"><span id="MathJax-Element-8-Frame" class="MathJax_SVG" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mrow is="true"><msubsup is="true"><mrow is="true"><mtext is="true">SO</mtext></mrow><mrow is="true"><mn is="true">3</mn></mrow><mrow is="true"><mo is="true">-</mo></mrow></msubsup></mrow></math>"><span class="MJX_Assistive_MathML">SO3-</span></span></span><span>) intermediate and H</span><sub>2</sub><span>O. Our results indicate that the </span><span class="math"><span id="MathJax-Element-9-Frame" class="MathJax_SVG" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mrow is="true"><mi mathvariant="normal" is="true">&#x3B4;</mi><msup is="true"><mrow is="true" /><mrow is="true"><mn is="true">18</mn></mrow></msup><msub is="true"><mrow is="true"><mtext is="true">O</mtext></mrow><mrow is="true"><msub is="true"><mrow is="true"><mtext is="true">SO</mtext></mrow><mrow is="true"><mn is="true">4</mn></mrow></msub></mrow></msub></mrow></math>"><span class="MJX_Assistive_MathML">δ18OSO4</span></span></span><span> values cannot be used to distinguish biological and abiotic, nor aerobic versus anaerobic, pathways of sphalerite oxidation. However, the </span><span class="math"><span id="MathJax-Element-10-Frame" class="MathJax_SVG" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mrow is="true"><mi mathvariant="normal" is="true">&#x3B5;</mi><msup is="true"><mrow is="true" /><mrow is="true"><mn is="true">18</mn></mrow></msup><msub is="true"><mrow is="true"><mtext is="true">O</mtext></mrow><mrow is="true"><msub is="true"><mrow is="true"><mtext is="true">SO</mtext></mrow><mrow is="true"><mn is="true">4</mn></mrow></msub><mo is="true">-</mo><msub is="true"><mrow is="true"><mtext is="true">H</mtext></mrow><mrow is="true"><mn is="true">2</mn></mrow></msub><mtext is="true">O</mtext></mrow></msub></mrow></math>"><span class="MJX_Assistive_MathML">ε18OSO4-H2O</span></span></span><span> values of ∼8‰ measured here are distinctly higher than </span><span class="math"><span id="MathJax-Element-11-Frame" class="MathJax_SVG" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mrow is="true"><mi mathvariant="normal" is="true">&#x3B5;</mi><msup is="true"><mrow is="true" /><mrow is="true"><mn is="true">18</mn></mrow></msup><msub is="true"><mrow is="true"><mtext is="true">O</mtext></mrow><mrow is="true"><msub is="true"><mrow is="true"><mtext is="true">SO</mtext></mrow><mrow is="true"><mn is="true">4</mn></mrow></msub><mo is="true">-</mo><msub is="true"><mrow is="true"><mtext is="true">H</mtext></mrow><mrow is="true"><mn is="true">2</mn></mrow></msub><mtext is="true">O</mtext></mrow></msub></mrow></math>"><span class="MJX_Assistive_MathML">ε18OSO4-H2O</span></span></span><span> values of ∼4‰ previously reported for pyrite oxidation indicating the influence of sulfide mineralogy on measured </span><span class="math"><span id="MathJax-Element-12-Frame" class="MathJax_SVG" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mrow is="true"><mi mathvariant="normal" is="true">&#x3B4;</mi><msup is="true"><mrow is="true" /><mrow is="true"><mn is="true">18</mn></mrow></msup><msub is="true"><mrow is="true"><mtext is="true">O</mtext></mrow><mrow is="true"><msub is="true"><mrow is="true"><mtext is="true">SO</mtext></mrow><mrow is="true"><mn is="true">4</mn></mrow></msub></mrow></msub></mrow></math>"><span class="MJX_Assistive_MathML">δ18OSO4</span></span></span><span> values.</span></p>
application/pdf
10.1016/j.gca.2011.10.022
en
Elsevier
Oxygen and sulfur isotope systematics of sulfate produced during abiotic and bacterial oxidation of sphalerite and elemental sulfur
article