Laboratory study of spectral induced polarization responses of magnetite - Fe2+ redox reactions in porous media
Laboratory study of spectral induced polarization responses of magnetite - Fe2+ redox reactions in porous media
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DOI：
10.1190/geo2013-0079.1
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发表时间：
2014-01-01
期刊：
影响因子：
3.3
通讯作者：
Shaw, Samuel
中科院分区：
文献类型：
--
作者：
Hubbard, Christopher G.;West, L. Jared;Shaw, Samuel
光谱激发极化（SIP）相位异常在污染场地的实地调查先前已被证明与化学还原条件和/或矿物的发生相关，但其原因尚不完全清楚。我们报告了一个系统的实验室调查的作用，磁铁矿和它的相互作用与氧化还原活性与氧化还原非活性离子在生产这样的相位异常。SIP响应的石英砂与5%的磁铁矿在含有氧化还原非活性的Ca 2+和Ni 2+与氧化还原活性的Fe 2+的溶液中，在整个pH值范围内测量对应于这些金属吸附到磁铁矿。对于氧化还原非活性离子Ca 2+和Ni 2+，SIP相响应显示在pH 4-10范围内没有变化，对应于它们的吸附，显示类似于30 mrad的异常，在类似于59-74 Hz处达到峰值。这些大的相位异常可能是由磁铁矿-溶液界面的极化引起的。随着氧化还原活性离子Fe 2+，峰值相位响应的频率逐渐降低，从类似于46到类似于3 Hz，流出物pH值从4增加到7，对应于Fe 2+到磁铁矿表面的渐进吸附。后者的频率（3赫兹）与其他地方报道的实地调查中检测到的相位异常大致对应。我们得出结论，pH值的敏感性产生从Fe 2+和磁铁矿表面之间的氧化还原反应，通过散装矿物的电荷转移，在其他实验室调查报告。我们的研究结果证实，SIP测量是敏感的氧化还原反应，涉及吸附的离子和矿物之间的电荷转移。因此，在地下水污染和生物刺激的实地调查中看到的相位异常可能是铁还原条件的指示，当磁铁矿等铁矿物存在时。
Spectral induced polarization (SIP) phase anomalies in field surveys at contaminated sites have previously been shown to correlate with the occurrence of chemically reducing conditions and/or semiconductive minerals, but the reasons for this are not fully understood. We report a systematic laboratory investigation of the role of the semiconductive mineral magnetite and its interaction with redox-active versus redox-inactive ions in producing such phase anomalies. The SIP responses of quartz sand with 5% magnetite in solutions containing redox-inactive Ca2+ and Ni2+ versus redox-active Fe2+ were measured across the pH ranges corresponding to adsorption of these metals to magnetite. With redox inactive ions Ca2+ and Ni2+, SIP phase response showed no changes across the pH range 4-10, corresponding to their adsorption, showing similar to 30 mrad anomalies peaking at similar to 59-74 Hz. These large phase anomalies are probably caused by polarization of the magnetite-solution interfaces. With the redox-active ion Fe2+, frequency of peak phase response decreased progressively from similar to 46 to similar to 3 Hz as effluent pH increased from four to seven, corresponding to progressive adsorption of Fe2+ to the magnetite surface. The latter frequency (3 Hz) corresponds approximately with those of phase anomalies detected in field surveys reported elsewhere. We conclude that pH sensitivity arises from redox reactions between Fe2+ and magnetite surfaces, with transfer of electrical charge through the bulk mineral, as reported in other laboratory investigations. Our results confirm that SIP measurements are sensitive to redox reactions involving charge transfers between adsorbed ions and semiconductive minerals. Phase anomalies seen in field surveys of groundwater contamination and biostimulation may therefore be indicative of iron-reducing conditions, when semiconductive iron minerals such as magnetite are present.