Bradford Scott A, Torkzaban Saeed, Walker Sharon L
US Salinity Laboratory, USDA-ARS, 450 W. Big Springs Road, Riverside, CA 92507-4617, USA.
Water Res. 2007 Jul;41(13):3012-24. doi: 10.1016/j.watres.2007.03.030. Epub 2007 May 2.
Filtration theory does not include the potential influence of pore structure on colloid removal by straining. Conversely, previous research on straining has not considered the possible influence of chemical interactions. Experimental and theoretical studies were therefore undertaken to explore the coupling of physical and chemical mechanisms of colloid straining under unfavorable attachment conditions (pH=10). Negatively charged latex microspheres (1.1 and 3 microm) and quartz sands (360, 240, and 150 microm) were used in packed column studies that encompassed a range in suspension ionic strengths (6-106 mM) and Darcy water velocities (0.1-0.45 cm min(-1)). Derjaguin-Landau-Verwey-Overbeek (DLVO) calculations and torque analysis suggests that attachment of colloids to the solid-water interface was not a significant mechanism of deposition for the selected experimental conditions. Effluent concentration curves and hyperexponential deposition profiles were strongly dependent on the solution chemistry, the system hydrodynamics, and the colloid and collector grain size, with greater deposition occurring for increasing ionic strength, lower flow rates, and larger ratios of the colloid to the median grain diameter. Increasing the solution ionic strength is believed to increase the force and number of colloids in the secondary minimum of the DLVO interaction energy profile. These weakly associated colloids can be funneled to small regions of the pore space formed adjacent to grain-grain junctions. For select systems, the ionic strength of the eluant solution was decreased to 6mM following the recovery of the effluent concentration curve. In this case, only a small portion of the deposited colloids was recovered in the effluent and the majority was still retained in the sand. These observations suggest that the extent of colloid removal by straining is strongly coupled to solution chemistry.
过滤理论并未涵盖孔隙结构对通过截留作用去除胶体的潜在影响。相反，先前关于截留作用的研究并未考虑化学相互作用的可能影响。因此，开展了实验和理论研究，以探讨在不利附着条件（pH = 10）下胶体截留的物理和化学机制的耦合。在填充柱研究中使用了带负电荷的乳胶微球（1.1和3微米）和石英砂（360、240和150微米），研究范围包括悬浮液离子强度（6 - 106 mM）和达西水流速（0.1 - 0.45 cm min⁻¹）。德亚金 - 朗道 - 韦弗 - 奥弗比克（DLVO）计算和扭矩分析表明，在所选择的实验条件下，胶体附着到固 - 水界面并非沉积的主要机制。流出物浓度曲线和超指数沉积剖面强烈依赖于溶液化学性质、系统流体动力学以及胶体和收集颗粒的尺寸，随着离子强度增加、流速降低以及胶体与中位粒径的比值增大，沉积量增加。据信，增加溶液离子强度会增加DLVO相互作用能曲线次级最小值中胶体的作用力和数量。这些弱结合的胶体可被引导至与颗粒 - 颗粒交界处相邻形成的孔隙空间的小区域。对于某些系统，在流出物浓度曲线恢复后，洗脱液的离子强度降至6 mM。在这种情况下，只有一小部分沉积的胶体在流出物中被回收，而大部分仍保留在沙子中。这些观察结果表明，通过截留作用去除胶体的程度与溶液化学性质密切相关。
