Earth Sciences Division, Lawrence, Berkeley National Laboratory, Berkeley, CA, USA.
Environ Sci Technol. 2010 Mar 1;44(5):1662-9. doi: 10.1021/es903277p.
Saturated packed column and micromodel transport studies were conducted to gain insight on mechanisms of colloid retention and release under unfavorable attachment conditions. The initial deposition of colloids in porous media was found to be a strongly coupled process that depended on solution chemistry and pore space geometry. During steady state chemical conditions, colloid deposition was not a readily reversible process, and micromodel photos indicated that colloids were immobilized in the presence of fluid drag. Upon stepwise reduction in eluting solution ionic strength (IS), a sharp release of colloids occurred in each step which indicates that colloid retention depends on a balance of applied (hydrodynamic) and resisting (adhesive) torques which varied with pore space geometry, surface roughness, and interaction energy. When the eluting fluid IS was reduced to deionized water, the final retention locations occurred near grain-grain contacts, and colloid aggregation was sometimes observed in micromodel experiments. Significant amounts of colloid retention hysteresis with IS were observed in the column experiments, and it depended on the porous medium (glass beads compared with sand), the colloid size (1.1 and 0.5 mum), and on the initial deposition IS. These observations were attributed to weak adhesive interactions that depended on the double layer thickness (e.g., the depth of the secondary minimum and/or nanoscale heterogeneity), colloid mass transfer on the solid phase to regions where the torque and force balances were favorable for retention, the number and extent of grain-grain contacts, and surface roughness.
进行了饱和填充柱和微模型传输研究，以深入了解在不利附着条件下胶体保留和释放的机制。发现胶体在多孔介质中的初始沉积是一个强烈耦合的过程，取决于溶液化学和孔隙空间几何形状。在稳定的化学条件下，胶体沉积不是一个容易可逆的过程，并且微模型照片表明，在存在流体阻力的情况下，胶体被固定。在逐步降低洗脱溶液离子强度（IS）的过程中，胶体在每一步都发生急剧释放，这表明胶体保留取决于施加的（流体动力）和抵抗（粘性）扭矩的平衡，而这些扭矩随着孔隙空间几何形状、表面粗糙度和相互作用能量而变化。当洗脱流体 IS 降低至去离子水时，最终保留位置出现在颗粒-颗粒接触附近，并且在微模型实验中有时观察到胶体聚集。在柱实验中观察到与 IS 相关的胶体保留滞后量很大，这取决于多孔介质（玻璃珠与砂相比）、胶体大小（1.1 和 0.5 微米）以及初始沉积 IS。这些观察结果归因于取决于双电层厚度的弱粘性相互作用（例如，次级最小值的深度和/或纳米级异质性）、胶体在固相上向有利于保留的扭矩和力平衡区域的质量转移、颗粒-颗粒接触的数量和程度以及表面粗糙度。
