U.S. Environmental Protection Agency, National Risk Management Research Laboratory, Ground Water and Ecosystems Restoration Division, 919 Kerr Research Drive, Ada, OK 74820, USA.
J Contam Hydrol. 2010 Jul 30;116(1-4):47-57. doi: 10.1016/j.jconhyd.2010.05.009. Epub 2010 May 31.
Predicting the long-term potential of permeable reactive barriers for treating contaminated groundwater relies on understanding the endpoints of biogeochemical reactions between influent groundwater and the reactive medium. Iron hydroxy carbonate (chukanovite) is frequently observed as a secondary mineral precipitate in granular iron PRBs. Mineralogical characterization was carried out using X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, and X-ray absorption spectroscopy on materials collected from three field-based PRBs in the US (East Helena, MT; Elizabeth City, NC; Denver Federal Center, CO). These PRBs were installed to treat a range of contaminants, including chlorinated organics, hexavalent chromium, and arsenic. Results obtained indicate that chukanovite is a prevalent secondary precipitate in the PRBs. Laboratory experiments on high-purity chukanovite separates were carried out to constrain the room-temperature solubility for this mineral. An estimated Gibbs energy of formation (Delta(f)G degrees) for chukanovite is -1174.4 +/- 6 kJ/mol. A mineral stability diagram is consistent with observations from the field. Water chemistry from the three reactive barriers falls inside the predicted stability field for chukanovite, at inorganic carbon concentrations intermediate to the stability fields of siderite and ferrous hydroxide. These new data will aid in developing better predictive models of mineral accumulation in zerovalent iron PRBs.
预测可渗透反应性屏障长期处理污染地下水的能力取决于了解进水与反应介质之间生物地球化学反应的终点。铁羟基碳酸盐（水羟铁华）通常作为颗粒铁 PRB 中的次生矿物沉淀而被观察到。使用 X 射线衍射、扫描电子显微镜、热重分析和 X 射线吸收光谱对从美国三个基于现场的 PRB（蒙大拿州东海伦娜；北卡罗来纳州伊丽莎白市；科罗拉多州丹佛联邦中心）采集的材料进行了矿物学特征描述。这些 PRB 被安装用于处理一系列污染物，包括氯化有机物、六价铬和砷。结果表明，水羟铁华是 PRB 中普遍存在的次生沉淀。对高纯度水羟铁华分离物进行了实验室实验，以限制该矿物的室温溶解度。水羟铁华的估计形成吉布斯自由能（Delta(f)G degrees）为-1174.4 +/- 6 kJ/mol。矿物稳定性图与现场观察结果一致。来自三个反应性屏障的水化学在水羟铁华的预测稳定场范围内，无机碳浓度介于菱铁矿和氢氧化亚铁的稳定场之间。这些新数据将有助于开发更好的零价铁 PRB 中矿物积累的预测模型。
