5:15 PM - 6:45 PM
[AGE28-P04] Roughness and Ionic strength effects on colloid movement in a saturated porous media
Keywords:Colloid, Surface roughness, Ionic strength, Deposition mechanism
The movement of colloids in porous media has recently garnered increased attention. Due to their substantial specific surface area and commendable structural stability, colloids serve as carriers that facilitate the transport of contaminants in soil. Previous studies have identified several factors influencing colloid movement, particularly solution ionic strength (IS). Notably, porous media have traditionally been perceived as smooth; however, they exhibit inherent surface roughness. In our research, we manipulated solution IS (1, 50, 75, 100mM) through varying concentrations of NaCl. Introducing roughness involves subjecting glass beads to HF treatment. By injecting solutions with different IS at various pore volumes of the column experiment, we explore the impact of IS and roughness on colloid deposition mechanisms in porous media.
Previous research indicated that colloid deposition was enhanced in porous media with rough surfaces. In our experiment, colloid mobility was enhanced in porous media of rough surfaces, and the fraction of reversibly captured colloids was decreased. This trend was particularly pronounced under high ionic strength (IS) conditions, specifically at 75mM and 100mM. Under 75 and 100mM conditions, in smooth porous media, the mobile fraction accounts for 47% and 35.6% of the total applied colloid, while the reversible colloid comprises 35.2% and 42.8% of the total applied colloid. However, in rough porous media, the mobile colloid constitutes 68% and 52.5% of the total colloids, with reversible colloids comprising 15.3% and 23.5% of the total colloids. The strained fraction of colloids can be attributed to the coupling of physical and chemical mechanisms, as discussed by Bradford et al. (2007). However, the straining fraction of colloids was comparable in both rough and smooth porous media for each IS condition. With an increase in IS from 1 to 100mM, strained colloids increased from 1.4% to 14.5% of total colloids in the smooth porous media and from 3.4% to 19.2% of total colloids in the rough surface porous media. Under 100 mM condition, SEM observations revealed that irreversible colloids were evenly distributed on smooth glass beads, whereas more colloids were irreversibly deposited in the concave regions of surface. By quantifying the irreversible attachment of colloids at the concave of HF-treated glass beads surfaces compared to the flat surfaces, the ratio ranged from approximately 2 to 15. This phenomenon align with previous studies indicating that the concave areas are more conducive to colloidal deposition compared to the convex regions of the rough surfaces.
Previous research indicated that colloid deposition was enhanced in porous media with rough surfaces. In our experiment, colloid mobility was enhanced in porous media of rough surfaces, and the fraction of reversibly captured colloids was decreased. This trend was particularly pronounced under high ionic strength (IS) conditions, specifically at 75mM and 100mM. Under 75 and 100mM conditions, in smooth porous media, the mobile fraction accounts for 47% and 35.6% of the total applied colloid, while the reversible colloid comprises 35.2% and 42.8% of the total applied colloid. However, in rough porous media, the mobile colloid constitutes 68% and 52.5% of the total colloids, with reversible colloids comprising 15.3% and 23.5% of the total colloids. The strained fraction of colloids can be attributed to the coupling of physical and chemical mechanisms, as discussed by Bradford et al. (2007). However, the straining fraction of colloids was comparable in both rough and smooth porous media for each IS condition. With an increase in IS from 1 to 100mM, strained colloids increased from 1.4% to 14.5% of total colloids in the smooth porous media and from 3.4% to 19.2% of total colloids in the rough surface porous media. Under 100 mM condition, SEM observations revealed that irreversible colloids were evenly distributed on smooth glass beads, whereas more colloids were irreversibly deposited in the concave regions of surface. By quantifying the irreversible attachment of colloids at the concave of HF-treated glass beads surfaces compared to the flat surfaces, the ratio ranged from approximately 2 to 15. This phenomenon align with previous studies indicating that the concave areas are more conducive to colloidal deposition compared to the convex regions of the rough surfaces.