Abstract:In order to understand about the impact of pore scale on colloid migration more deep, migration processes of colloid in acid-washed glass beads/quartz, Milli-Q-washed glass beads/quartz were compared under different pH and ionic strength. Results showed that the pore scale of glass beads with the same shape (porosity 0.38) was smaller than that of quartz sand with various shapes (porosity 0.45), although the glass beads and quartz sand had a uniform particle size (0.45~0.60 mm). The surface components of glass beads changed at a very small range from 0 to 0.6% after acid washing and Milli-Q washing. The acid-washed media could provide more favorable adsorption sites. The colloid retention of quartz sand increased after the acid washing or Milli-Q washing(72.1% and 69.2%, respectively) when the pH of the solution raised to 10. The enhancement of adsorption was induced by pore scale retention mechanism, such as retention in particle contact points, non-flowing area or low velocity area and eddy current area, which could not be explained by the DLVO theory. The retention of colloid in the acid-washed quartz sand was about 16.3% and 28.0% higher than that of the acid-washed glass beads under the environments of ion strength of 0.001 mol/L and 0.05 mol/L, respectively, which implied that increased pore scale enhanced colloid retention in particle contact points, non-flowing area or low velocity area and eddy current area. However, occurrence of preferential flow in soil columns impaired the retention of colloid in pores greatly. In addition, only a small parts of colloids (<3.9%) was desorbed from eddy zones in the glass beads and the quartz sand after using ultra-pure water, indicating that the colloid retention in the eddy zones wasn't the dominant mechanism.