Coupled effects of high pH and chemical heterogeneity on colloid retention and release in saturated porous media

Abstract

The transport of colloid in saturated porous media is of great significance for the assessment of environmental risk and bioremediation. However, coupled effects of high pH and chemical heterogeneity on colloid retention and release in saturated porous media remain unclear. We studied colloid transports in acid treated/untreated glass beads under various high pH values and ionic strength (IS) conditions to elucidate the effect of high pH and chemical heterogeneity. Chemical impurities promote the colloid to attach to the primary minimum. Increasing environmental pH of solutions would weaken the colloidal retention capacity. Once pH increases to 11, almost no colloid retention occurs no matter chemical impurities exist or not. Adsorbed colloids in the primary minimum can be detached at high pH environments (from 10 to 12). Despite the final similar environmental pH (from 10 to 12), different amounts of colloids are reserved at the ends of the attaching processes and eluting processes. Effects of chemical impurities on colloid retention are negligible when pH = 10 or higher. At the same time, colloid release in high pH solution is also related to disabled chemical impurities. Although previous studies show no obvious rule about colloid release with changing pH (from 6.8–10), our results demonstrate significant coupled effects of high pH and chemical heterogeneity on colloid retention and release in saturated porous media. We also found that straining might be underestimated. Our results improve the understanding about the role of pH in colloid transport processes.