Collaborative Research: The Advance of Colloid Mobilization and Transport Fronts

9418172消除地下水中放射性核素、金属和非极性有机化合物的运输受到固定含水层沉积物吸附的严重限制。然而，在胶体存在的情况下，这些低溶解度污染物的迁移距离比只考虑污染物在溶解和吸附的固定相之间的分布的模型预测的距离要大得多。胶体的存在要求在传输模型中包含污染物的吸附的、流动的相。这一要求将我们的注意力转移到了含水层中胶体的动员、运输和沉积上。胶体的形成可通过含水层中的化学或物理扰动引起的就地沉淀或动员而发生。当化学扰动增加胶体和颗粒表面之间的排斥力时，胶体就会被动员起来，并与地下水一起输送。如果引起这种扰动的溶质的传输相对于地下水来说是缓慢的，那么被动员的胶体最终将通过溶质前沿，遇到尚未受到溶质或胶体动员剂影响的沉积物。在这种情况下，我们预计胶体会重新沉积在颗粒上，并一直留在那里，直到溶质“赶上”。我们假设，通过化学扰动动员的胶体的运输永远不会超过胶体动员剂的运输。为了验证这一假设，我们建议(1)建立一个模型，同时解释胶体和胶体动员剂的运输，以及(2)进行一系列模拟和测试胶体动员剂和胶体动员剂的小规模、中型和现场实验。该模型将由加州大学洛杉矶分校的研究人员开发和严格测试。该模型将考虑胶体沉积和释放、胶体和颗粒表面的微观和宏观电荷不均质性、保留胶体对胶体沉积和释放的影响、溶质吸附和解吸以及“大尺度”非均质性(即在含水层沉积物中的分布)。对于实验室实验，它将被用来模拟一维和二维的胶体和溶质运移，而对于野外实验，它将扩展到三维。小规模和中型实验将在科罗拉多大学的水资源实验室进行。实验中使用的材料包括赤铁矿和高岭石胶体，石英和氢氧化铁包裹的石英多孔介质，以及磷酸十二酸(一种表面活性剂)，并从现场分离NOM作为胶体动员剂。将进行小规模的柱实验，以确定中尺度和现场实验的参数。中等规模的实验将在一个长10米、高2米、宽5厘米的二维储罐中进行，储罐内填充着均匀和非均匀(层状)的多孔介质。储罐实验将直接检验胶体运输与胶体动员剂运输之间的关系。野外实验将在南卡罗来纳州乔治敦的巴鲁奇森林科学研究所场地进行。BFSI场地的地表含水层主要由石英砂、氢氧化铁和层状非均质性组成。建议进行一项现场实验，以检验合成高岭石的沉积和动员，这些高岭石被标记为稳定的同位素(氚或18O)或钛作为硅的同构替代品。单独的注射将测试来自附近池塘的十二酸和富含NOM的水作为胶体动员剂在含水层的氧化和亚缺氧部分的效果。

9418172 Elimelech The transport of radionuclides, metals, and non-polar organic compounds in groundwater is severely restricted by adsorption to immobile aquifer sediments. In the presence of colloids, however, these low-solubility contaminants migrate over distances much greater than those predicted by models that consider only the distribution of the contaminant between the dissolved and the adsorbed, immobile phase. The presence of colloids requires inclusion of an adsorbed, mobile phase of the contaminant in transport models. This requirement has shifted our attention to the mobilization, transport, and deposition colloids in aquifers. Colloid formation may occur by in situ precipitation or mobilization caused by chemical or physical perturbations in the aquifer. When a chemical perturbation increases the repulsive forces between the colloid and grain surfaces, colloids are mobilized and transported with the groundwater. If the transport of the solute causing that perturbation is retarded relative to the groundwater, the mobilized colloid will eventually pass the solute front and encounter sediments that have not yet been affected by the solute, or colloid-mobilizing agent. Under these conditions, we expect that the colloids will be re-deposited on grains and will remain there until the solute "catches up." We hypothesize that the transport of colloids mobilized by a chemical perturbation will never exceed the transport of the colloid-mobilizing agent. To test this hypothesis, we propose to (1) develop a model that will simultaneously account for the transport of the colloids and the colloid-mobilizing agent and (2) conduct a series of small-scale, intermediate-scale, and field experiments simulating and testing colloid mobilization and transport. The model will be developed and rigorously tested by the UCLA researchers. The model will account for colloid deposition and release, microscopic and macroscopic charge heterogeneity of colloid and grain surfaces, the effect of retained colloids on the deposition and release of colloids, solute adsorption and desorption, and "megascopic" heterogeneities (i.e., laying in aquifer sediments). It will be formulated to model colloid and solute transport in one and two dimensions for the laboratory experiments and it will be extended to three dimensions for the field experiment. The small-and intermediate-scale experiments will be conducted at the University of Colorado's Water Resources laboratory. The materials used in the experiments will include hematite and kaolinite colloids, quartz and ferric oxyhydroxide-coated quartz porous media, and phosphate dodecanoic acid (a surfactant), and isolate NOM from the field site as colloid-mobilizing agents. Small-scale column experiments will be conducted to identify parameters for the intermediate-scale and field experiments. The intermediate-scale experiments will be conducted in a two-dimensional tank of 10 m length 2 m height, and 5 cm width filled with homogeneous and heterogeneous (layered) porous media. The tank experiments will directly test the hypothesis relating colloid transport to the transport of the colloid-mobilizing agent. The field experiment will be conducted at the Barouch Forest Science Institute site in Georgetown, S.C. The surficial aquifer at the BFSI site is composed primarily of quartz sand, ferric oxyhydroxides, and layered heterogeneity. A field experiment is proposed that will examine the deposition and mobilization of synthesied kaolinite collids labeled with a stable isotope (deuterium or 18O) or titanium as an isomorphous substitute for silicon. Separate injections will test the effects of dodecanoic acid and NOM-rich water from a nearby pond as the colloid-mobilizing agent in both oxic and suboxic portions of the aquifer.