Oxygen and sulfur isotope systematics of sulfate produced by bacterial and abiotic oxidation of pyrite
Oxygen and sulfur isotope systematics of sulfate produced by bacterial and abiotic oxidation of pyrite
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DOI：
10.1016/j.gca.2007.04.017
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发表时间：
2007-08-01
影响因子：
5
通讯作者：
Mandernack, Kevin W.
中科院分区：
文献类型：
--
作者：
Balci, Nurgul;Shanks, Wayne C., III;Mandernack, Kevin W.
为了更好地了解酸性矿井水（AMD）等自然环境中黄铁矿氧化的反应途径及对硫酸盐生成的δ O-18和δ S-34值的地球化学控制，在实验室进行了一系列黄铁矿氧化实验。我们的生物和非生物实验进行了有氧条件下使用O-2作为氧化剂和在厌氧条件下使用溶解的Fe（III）（aq）作为氧化剂与不同的δ 18 OH，O值的存在和不存在的嗜酸氧化亚铁硫杆菌。此外，需氧生物实验被设计为短期和长期实验，其中最终pH分别控制在2.7和2.2。由于非生物硫化物氧化的动力学较慢，仅在最终pH值接近2.7的情况下长期进行有氧非生物实验。从生物和非生物厌氧实验的δ S-34（SO 4）值表明一个小的，但显着的硫同位素分馏（类似于千分之-0.7）相比，没有显着的分馏观察到的任何有氧实验。水衍生的氧和溶解氧（O-2）的掺入硫酸盐的相对百分比进行了估计，除了硫酸盐和水之间的氧同位素分馏，和溶解氧。正如预期的那样，在生物和非生物厌氧实验期间，所有的硫酸盐氧都来自水。在O-2的氧化实验过程中，水衍生的氧掺入硫酸盐的百分比随培养时间的延长和pH值的降低而变化，但不是由于细菌的存在或不存在。根据短期生物防治、长期生物防治和非生物防治试验，这些百分比分别估计为85%、92%和87%。硫酸盐和水之间的氧同位素分馏效应（SO 4 O-18（SO 4）-H2O）的类似千分之3.5份被确定为厌氧（生物和非生物）实验。然后用测得的δ（18）O（SO 4）2-H2O值估算好氧实验中硫酸盐和溶解氧之间的氧同位素分馏效应（δ（18）O（SO 4）2-O-2），短期生物、长期生物和非生物控制实验中的分馏效应分别为-10.0ppm、-10.8%和-9.8ppm。基于生物和非生物实验中δ O-18（SO_4）值的相似性，认为δ O-18（SO_4）值不能用来区分黄铁矿氧化的生物和非生物机制。结果表明，在pH < 3时，Fe（Ⅲ）2，q是黄铁矿的主要氧化剂，即使在溶解氧存在下也是如此;在好氧和厌氧条件下，硫酸盐的主要氧源都是水-氧。(c)2007爱思唯尔有限公司版权所有。
To better understand reaction pathways of pyrite oxidation and biogeochemical controls on delta O-18 and delta S-34 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 O-2 as an oxidizing agent and under anaerobic conditions by using dissolved Fe(III)(aq) as an oxidant with varying delta 18OH,O 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 similar to 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 similar to 2.7. The delta S-34(SO4) values from both the biological and abiotic anaerobic experiments indicated a small but significant sulfur isotope fractionation (similar to-0.7 parts per thousand) 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 (O-2) 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 O-2 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 (epsilon O-18(SO4)-H2O) of similar to 3.5 parts per thousand was determined for the anaerobic (biological and abiotic) experiments. This measured epsilon(18)O(SO4)2--H2O value was then used to estimate the oxygen isotope fractionation effects (epsilon(18)O(SO4)2-O-2) between sulfate and dissolved oxygen in the aerobic experiments which were -10.0 parts per thousand, -10.8%, and -9.8 parts per thousand, for the short-term biological, long-term biological and abiotic control experiments, respectively. Based on the similarity between delta O-18(SO4), values in the biological and abiotic experiments, it is suggested that delta O-18(SO4) values cannot be used to distinguish biological and abiotic mechanisms of pyrite oxidation. The results presented here suggest that Fe(III),,q 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. (c) 2007 Elsevier Ltd. All rights reserved.