The release of Brownian colloids from silica surfaces in aqueous media

Fundamental aspects of the release of colloids from silica surfaces in aqueous media were studied using several experimental techniques.; The effect of particle size on colloid release predicted by the DLVO theory was investigated using both polystyrene latex and silica colloids in packed flow-through columns. Colloid release was found to strongly depend on the model porous media pre-treatment method. Several recommendations are given to ensure both correct and consistent experimental results. In order to facilitate the comparison between release experiments conducted under different conditions, the new dimensionless colloid release efficiency Ω is introduced. The release experiments were successfully modeled using the convection diffusion equation coupled with a two-population model consisting of irreversibly and reversibly attached colloids. The colloid size effect predicted by the DLVO theory was not found. The experimental release efficiencies were orders of magnitude larger than the theoretical release efficiencies and showed an inverse dependence on the deposition ionic strength. Surface heterogeneities and double layer dynamics are suggested as likely explanations for the discrepancies between theory and experiments. The feasibility of secondary minimum release was also studies but found to play a negligible role in the release of Brownian colloids.; Using fluorescence polystyrene colloids and epi-fluorescence microscopy the effect of colloid size was also investigated using the stagnation point flow experimental technique. Colloid release was successfully modeled by assuming a Weibull probability distribution for the release activation energies. While a size dependence for both colloid deposition and release was found, the results remain inconclusive due to differences in the surface charge densities of the colloids. The mass transfer aspect of colloid release was also investigated. The release efficiencies increased with increasing flow rates at high pH conditions, however for low ionic strength conditions it decreased with increasing flow rates. This is contrary to theoretical expectations. In order to explain this divergence, a hypothesis based on double layer dynamics specific to amorphous silica surfaces is presented.; To evaluate a natural zeolite as a candidate material for a permeable reactive barrier for the removal of radioactive strontium from groundwater, the effect of particle release on permeability reductions and colloid facilitated transport of strontium was investigated. The introduction of low ionic strength solutions in packed zeolite/sand flow-through columns resulted in large quantities of particle release and subsequent reductions in hydraulic conductivities in varying severity. Remedies in the form of different zeolite pre-treatment are suggested. Using an intermediate scale two-dimensional aquifer tank containing a zeolite barrier saturated with strontium, it was shown that the generation of zeolite particles due to changes in solution chemistry can lead to colloid facilitated strontium transport.