Double Layer Interaction Model and Particle Concentration Effect in Water
Abstract
The observation that an increase in particle concentration increases the solute concentration has been noted by a number of investigators. This phenomenon is very important to re-suspension of particles and contaminant release and diagenesis. Various reasons for this effect have been proposed. This study investigates the role of repulsive forces acting among particles when they are close to one another (e.g. double layers overlap).
The approach was to assess all possible forces theoretically. The only significant long range force is the columbic force which is shown to increase the solute concentration. A double layer interaction (DLI) model was developed based on this theory. The predicted ionic strength effect is the same as has been observed experimentally. The model gives limits for the particle concentration effect.
In other experiments, a Couette device was also constructed to examine the impact of inter-particle collision on adsorption.
Environmental implications of the particle concentration effect are that desorption (of contaminants) can occur up to 30% for clay sized particles in fresh water (ionic strength less than 0.1 m/l).