Schaefer Charles E, Ho Paul, Gurr Christopher, Berns Erin, Werth Charles
CDM Smith, 110 Fieldcrest Avenue, #8, 6th Floor, Edison, NJ 08837, United States.
CDM Smith, 14432 SE Eastgate Way # 100, Bellevue, WA 98007, United States.
J Contam Hydrol. 2017 Nov;206:10-17. doi: 10.1016/j.jconhyd.2017.09.007. Epub 2017 Sep 21.
Laboratory batch experiments were performed to assess the impacts of temperature and mineralogy on the abiotic dechlorination of tetrachloroethene (PCE) or trichloroethene (TCE) due to the presence of ferrous minerals in natural aquifer clayey soils under anaerobic conditions. A combination of x-ray diffraction (XRD), magnetic susceptibility, and ferrous mineral content were used to characterize each of the 3 natural soils tested in this study, and dechlorination at temperatures ranging from 20 to 55°C were examined. Results showed that abiotic dechlorination occurred in all 3 soils examined, yielding reduced gas abiotic dechlorination products acetylene, butane, ethene, and/or propane. Bulk first-order dechlorination rate constants (k), scaled to the soil:water ratio expected for in situ conditions, ranged from 2.0×10day at 20°C, to 32×10day at 55°C in the soil with the greatest ferrous mineral content. For the generation of acetylene and ethene from PCE, the reaction was well described by Arrhenius kinetics, with an activation energy of 91kJ/mol. For the generation of coupling products butane and propane, the Arrhenius equation did not provide a satisfactory description of the data, likely owing to the complex reaction mechanisms associated with these products and/or diffusional mass transfer processes associated with the ferrous minerals likely responsible for these coupling reactions. Although the data set was too limited to determine a definitive correlation, the two soils with elevated ferrous mineral contents had elevated abiotic dechlorination rate constants, while the one soil with a low ferrous mineral content had a relatively low abiotic dechlorination rate constant. Overall, results suggest intrinsic abiotic dechlorination rates may be an important long-term natural attenuation component in site conceptual models for clays that have the appropriate iron mineralogy.
进行了实验室批量实验，以评估温度和矿物学对厌氧条件下天然含水层黏性土壤中由于亚铁矿物的存在而导致的四氯乙烯（PCE）或三氯乙烯（TCE）非生物脱氯的影响。结合X射线衍射（XRD）、磁化率和亚铁矿物含量来表征本研究中测试的3种天然土壤中的每一种，并研究了20至55°C温度范围内的脱氯情况。结果表明，在所研究的所有3种土壤中均发生了非生物脱氯，产生了脱氯气体非生物脱氯产物乙炔、丁烷、乙烯和/或丙烷。按原位条件下预期的土壤与水的比例进行缩放后的总体一级脱氯速率常数（k），在亚铁矿物含量最高的土壤中，范围从20°C时的2.0×10⁻³天⁻¹到55°C时的32×10⁻³天⁻¹。对于由PCE生成乙炔和乙烯的反应，Arrhenius动力学能很好地描述该反应，活化能为91kJ/mol。对于生成耦合产物丁烷和丙烷的反应，Arrhenius方程不能令人满意地描述数据，这可能是由于与这些产物相关的复杂反应机制和/或与可能导致这些耦合反应的亚铁矿物相关的扩散传质过程。尽管数据集有限，无法确定明确的相关性，但亚铁矿物含量较高的两种土壤具有较高的非生物脱氯速率常数，而亚铁矿物含量较低的一种土壤具有相对较低的非生物脱氯速率常数。总体而言，结果表明，对于具有合适铁矿物学的黏土，本征非生物脱氯速率可能是场地概念模型中一个重要的长期自然衰减组分。
