Department of Civil, Environmental and Ocean Engineering, Stevens Institute of Technology, Castle Point on Hudson, Hoboken, NJ 07030, USA.
Department of Civil, Environmental and Ocean Engineering, Stevens Institute of Technology, Castle Point on Hudson, Hoboken, NJ 07030, USA.
J Contam Hydrol. 2018 Feb;209:24-32. doi: 10.1016/j.jconhyd.2018.01.003. Epub 2018 Feb 2.
Hydraulic fracturing (or fracking) is a well stimulation technique used to extract resources from a low permeability formation. Currently, the most common application of fracking is for the extraction of oil and gas from shale. During the operation, a large volume of brine, rich in hazardous chemicals, is produced. Spills of brine from wells or pits might negatively impact underground water resources and, in particular, one of the major concerns is the migration of radionuclides, such as radium (Ra), into the shallow subsurface. However, the transport behaviour of Ra through a reactive porous medium under conditions typical of a brine, i.e., high salinity, is not well understood, yet. Here, a study on the transport behaviour of barium (Ba, congener of radium) through a porous medium containing a common mineral such as goethite (FeO(OH)) is presented. Batch and column flood tests were carried out at conditions resembling the produced brine, i.e., large values of ionic strength (I), namely, 1 to 3mol/kg. The measurements were described with the triple layer surface complexation model coupled with the Pitzer activity coefficient method and a reactive transport model, in the case of the transport tests. The experimental results show that the adsorption of Ba onto FeO(OH) increases with pH but decreases with I and it becomes negligible at the brine conditions. Moreover, even if isotherms show adsorption at large I, at the same conditions during transport, Ba travels without retardation through the FeO(OH) porous medium. The triple layer model agrees very well with all batch data but it does not describe well the transport tests in all cases. In particular, the model cannot match the pH measurements at large I values. This suggests that the chemical reactions at the solid-liquid interface do not capture the mechanism of Ba adsorption onto FeO(OH) at large salinity. Finally, this study suggests that barium, and potentially its congeners, namely, radium, calcium, magnesium, and strontium, may travel at the average flow velocity through a soil where the dominant reactive mineral is goethite.
水力压裂（或压裂）是一种用于从低渗透性地层中提取资源的井刺激技术。目前，压裂最常见的应用是从页岩中提取石油和天然气。在作业过程中，会产生大量富含危险化学品的盐水。来自井或坑的盐水溢出可能会对地下水资源产生负面影响，特别是人们主要关注的是放射性核素（如镭（Ra））迁移到浅层地下。然而，在类似于盐水的条件下，即高盐度下，镭通过反应性多孔介质的传输行为尚未得到很好的理解。在这里，研究了钡（Ba，镭的同系物）通过含有常见矿物如针铁矿（FeO（OH））的多孔介质的传输行为。在类似于生产盐水的条件下，即大离子强度（I），即 1 至 3mol/kg 下进行了批量和柱洪水试验。在传输试验中，使用带有 Pitzer 活度系数法和反应性传输模型的三层表面络合模型对测量结果进行了描述。实验结果表明，Ba 在 FeO（OH）上的吸附随 pH 增加而增加，但随 I 减小而减小，在盐水条件下可忽略不计。此外，即使在大 I 下的等温线显示出吸附，在相同条件下进行传输时，Ba 也会无阻地通过 FeO（OH）多孔介质。三层模型与所有批处理数据非常吻合，但并非在所有情况下都能很好地描述传输测试。特别是，该模型无法在大 I 值下匹配 pH 测量值。这表明在固-液界面上的化学反应无法捕获在大盐度下 Ba 吸附到 FeO（OH）的机制。最后，本研究表明，钡（以及潜在的同系物，即镭、钙、镁和锶）可能以土壤中主要反应性矿物为针铁矿的平均流速通过土壤。
