Effects of solution chemistry on straining of colloids in porous media under unfavorable conditions

This study examines effects of solution chemistry on straining of colloids in porous media under unfavorable conditions via theoretical analysis and laboratory column experiments. Geometric analysis was used to estimate the effects of solution chemistry on the critical straining ratio of colloid diameter (d(p)) to collector diameter (d(c)), above which straining occurs. Column experiments were conducted with various sizes of latex particles and glass beads at different solution ionic strengths. A two-or three-step procedure was used to measure colloid rentention and release by monitoring effluent colloid concentrations, and the columns were dissected at the end of experiments to determine distribution profiles of retained colloids. Measured effluent breakthrough curves and spatial deposition profiles were modeled with the convection-diffusion equation including terms of attachment and straining. The experimental results confirm our theoretical analysis that the critical straining ratio is significantly reduced at higher ionic strength due to additional straining induced by attachment, predominantly at the grain-to-grain contacts. Through systematic evaluation of contributions of physical and physiochemical factors to colloid straining, this study provides explanations for the inconsistent and wide range of d(p)/dc ratios reported in the literature as well as some of the reported limitations of filtration theory.