Particle size effects on colloid deposition kinetics: evidence of secondary minimum deposition

Abstract

Abstract The influence of particle size on the deposition kinetics of several submicron carboxyl latex spheres, sulfate latices, and hematite particles was examined in granular quartz beds as a function of ionic strength. Experiments were performed near pH 10 in the presence of sodium dodecyl sulfate to reduce surface heterogeneity by masking possible hydrophobic regions on the interacting surfaces. The onset of unfavorable filtration conditions and the sensitivity of the experimental attachment effciencies, α exp , to changes in the ionic strength were both particle size dependent. The influences of pH and ionic strength, however, were opposite to those predicted by filtration theory based on the primary interaction energy barrier height. Correlations of α exp with the secondary minimum of the interaction energy showed that, as attachment efficiencies approached unity, the depth of the secondary well increased. These observations suggest that particles may be retained within the secondary minimum even when an energy barrier is sufficient to inhibit attachment in the primary energy well. This hypothesis was further supported by particle detachment experiments which revealed that approximately 80% of the particles attached under unfavorable deposition conditions could be released when the secondary minimum was eliminated.