Princeton University, Princeton, New Jersey, USA.
J Contam Hydrol. 2012 Apr 1;131(1-4):89-99. doi: 10.1016/j.jconhyd.2012.02.002. Epub 2012 Feb 9.
At the former nuclear weapon production site in Hanford, WA, caustic radioactive tank waste leaks into subsurface sediments and causes dissolution of quartz and aluminosilicate minerals, and precipitation of sodalite and cancrinite. This work examines changes in pore structure due to these reactions in a previously-conducted column experiment. The column was sectioned and 2D images of the pore space were generated using backscattered electron microscopy and energy dispersive X-ray spectroscopy. A pre-precipitation scenario was created by digitally removing mineral matter identified as secondary precipitates. Porosity, determined by segmenting the images to distinguish pore space from mineral matter, was up to 0.11 less after reaction. Erosion-dilation analysis was used to compute pore and throat size distributions. Images with precipitation had more small and fewer large pores. Precipitation decreased throat sizes and the abundance of large throats. These findings agree with previous findings based on 3D X-ray CMT imaging, observing decreased porosity, clogging of small throats, and little change in large throats. However, 2D imaging found an increase in small pores, mainly in intragranular regions or below the resolution of the 3D images. Also, an increase in large pores observed via 3D imaging was not observed in the 2D analysis. Changes in flow conducting throats that are the key permeability-controlling features were observed in both methods.
在华盛顿州汉福德的前核武器生产现场，腐蚀性放射性罐废物渗入地下沉积物，并导致石英和铝硅酸盐矿物溶解，以及方钠石和钙霞石沉淀。这项工作研究了在先前进行的柱实验中这些反应导致的孔隙结构变化。将柱子分段，并使用背散射电子显微镜和能量色散 X 射线光谱法生成孔隙空间的 2D 图像。通过数字去除被识别为次生沉淀的矿物质，创建了预沉淀情景。通过将图像分段以区分孔隙空间和矿物质来确定孔隙率，反应后孔隙率降低了高达 0.11。侵蚀-扩张分析用于计算孔隙和喉道尺寸分布。有沉淀的图像具有更多的小孔隙和更少的大孔隙。沉淀减少了喉道尺寸和大喉道的丰度。这些发现与基于 3D X 射线 CMT 成像的先前发现一致，观察到孔隙率降低、小喉道堵塞以及大喉道几乎没有变化。然而，2D 成像发现小孔隙增加，主要在颗粒内区域或 3D 图像的分辨率以下。此外，在 3D 成像中观察到的大孔隙增加在 2D 分析中没有观察到。两种方法都观察到了控制渗透率的关键流导喉道的变化。
