Inhaltszusammenfassung

Column breakthrough experiments with carboxylated polystyrene microspheres in saturated wettable and hydrophobic sand at different ionic strengths were conducted to investigate the effect of grain water repellency on colloid transport and deposition behavior. Total interaction free energies calculated from zeta (ζ)-potential and contact angle data were used to explain the specific colloid breakthrough behavior. Colloid breakthrough behavior could be well described with the finite-element code...Column breakthrough experiments with carboxylated polystyrene microspheres in saturated wettable and hydrophobic sand at different ionic strengths were conducted to investigate the effect of grain water repellency on colloid transport and deposition behavior. Total interaction free energies calculated from zeta (ζ)-potential and contact angle data were used to explain the specific colloid breakthrough behavior. Colloid breakthrough behavior 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 (gs– = 1.6 × 10–2 mJ m–2, as compared to gs– = 64.1 mJ m–2 for the wettable sand), leading to strongly attractive acid–base interactions at separation distances < 5 nm, but also by weaker repulsive electrostatic interactions due to a lower ζ-potential of the hydrophobic surfaces (ζ = –38 mV, as compared to ζ = –46 mV for the wettable sand, in deionized water). Increasing ionic strength reduced the repulsive electrostatic interaction and generally increased colloid deposition with the effect being more pronounced in the hydrophobic matrix. It can be concluded that grain water repellency tends to increase the deposition of negatively charged hydrophilic colloids, which can be described by specific acid–base interactions. However, calculated absolute values of total interaction free energy should be interpreted with caution as surface nonidealities such as chemical heterogeneity may lead to deviations from the actual interaction energy conditions.» weiterlesen» einklappen

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