Water repellency enhances the deposition of negatively charged hydrophilic colloids in a water-saturated sand matrix

Abstract The effect of grain water repellency on transport and deposition of hydrophilic colloids was studied by analyzing the breakthrough behavior of carboxylate-modified microspheres in water-saturated wettable and hydrophobic sand columns at different ionic strengths. Interaction free energies calculated from zeta ( ζ )-potential and contact angle data were used to explain the specific colloid breakthrough behavior. Experimental breakthrough data could be well described with the finite-element code HYDRUS-1D using a one kinetic site model with attachment and detachment kinetics. Higher colloid deposition rates found for the hydrophobic sand could primarily be explained by its small electron-donor component of surface free energy ( γ s −  = 1.6 × 10 −2  mJ m −2 , compared to γ s −  = 64.1 mJ m −2 for the wettable sand), leading to strongly attractive acid–base interactions at separation distances