Bridge Jonathan W, Banwart Steven A, Heathwaite A Louise
Cell-Mineral Interface Research Programme, Kroto Research Institute, North Campus, University of Sheffield, Broad Lane, Sheffield S3 7HQ, United Kingdom.
Environ Sci Technol. 2007 Dec 15;41(24):8288-94. doi: 10.1021/es071155a.
Colloid deposition in unsaturated, nonuniform porous media is poorly explained by current models and difficult to measure using breakthrough curves and retained mass profiles. We present new methods which enable time-lapse fluorescence imaging to quantify variations in pore saturation, theta, and colloid deposition in 2D, nonuniform unsaturated flow fields. Calibration experiments revealed direct proportionality between fluorescence F and theta in 20/30 mesh quartz sand. Analysis of breakthrough data in fluorescence images allows quantification of the mean mobile concentration, mean deposition rate, and hence the colloid removal efficiency eta directly from data at the pixel-scale throughoutthe flow field. We imaged carboxylate-modified latex microspheres from a point source in saturated flow and unsaturated flow across a capillary fringe at 10(-3), 10(-2), and 10(-1) M NaCl. Total numbers of colloids deposited and values of eta increased with ionic strength. We modeled the observed variations in eta with theta to estimate the partitioning of colloid deposition between air-water and solid-water interfaces. In the broad saturation range 0.2 < theta < 1, our results suggest that only at the lowest ionic strength, where deposition at solid-water interfaces was strongly unfavorable, did colloid deposition associated with air-water interfaces significantly influence the total colloid removal.
目前的模型难以很好地解释胶体在非饱和、非均匀多孔介质中的沉积情况，并且使用穿透曲线和保留质量剖面来测量也很困难。我们提出了新的方法，能够通过延时荧光成像来量化二维非均匀非饱和流场中孔隙饱和度（θ）的变化以及胶体的沉积情况。校准实验表明，在20/30目石英砂中，荧光强度F与θ之间存在直接的比例关系。对荧光图像中的穿透数据进行分析，可以直接从整个流场像素尺度的数据中量化平均流动浓度、平均沉积速率，进而量化胶体去除效率η。我们对饱和流和穿过毛细边缘的非饱和流中，在10⁻³、10⁻²和10⁻¹ M氯化钠条件下，点源处的羧酸盐改性乳胶微球进行了成像。沉积的胶体总数和η值随离子强度的增加而增加。我们对观察到的η随θ的变化进行建模，以估计胶体在气 - 水界面和固 - 水界面之间沉积的分配情况。在0.2 < θ < 1的较宽饱和度范围内，我们的结果表明，只有在最低离子强度下，即固 - 水界面处的沉积非常不利时，与气 - 水界面相关的胶体沉积才会对总胶体去除产生显著影响。
