Effects of Ionic Strength on Fine Particle Clogging of Soil Filters

The effects of ionic strength of the permeating fluid on the clogging of soil filters and drainage layers are addressed using both experimental and modeling investigations. In the experimental phase, a sandy soil representative of soil filters was permeated with pore fluids containing kaolinite particles. The ionic strength of the solutions was changed using different concentrations of NaOH and KCl. The permeability reductions of the soil filter were determined by varying pore fluid and particle suspension parameters. Higher ionic strength caused more flocculation of the kaolinite particles and resulted in more rapid reduction of permeability. In the modeling phase, a physical clogging model developed previously by the authors, was used to account for the ionic strength effects. A lumped parameter ${\theta }_0$ was used in the model to account for the ionic strength of the pore fluid and the several interparticle forces, for example gravitational, inertial, hydrodynamic, electric double layer, and van der Waals forces. The effect of the lumped parameter ${\theta }_0$ on the permeability reduction was found to be greater than the effect of the sizes of the influent particles. For the same ionic strengths, NaOH resulted in larger flocs of kaolinite particles than KCl, and caused more rapid reduction in permeability.