Physicochemical aspects of the kinetics of aggregation: A modeling and experimental study

This thesis had two objectives: the formulation of a mathematical model to study the sensitivity of particle aggregation with respect to different physicochemical parameters; and the correlation of the partitioning of chemical moieties between the solid/water interface with particle stability.; The numerical model developed for the description of particle aggregation and settling had two major differences when compared with traditional modeling. An alternating operator splitting technique (AOST) that solved the aggregation and transport terms sequentially was used to solve the aggregation/transport kernel. The residence-time scheme (RTS), a methodology based on the individual residence times in the spatial discretization of each particle size fraction, was used to solve the settling term. RTS eliminated numerical diffusion, an artifact present when using the traditional upwind first-order finite-difference scheme. Simulation results indicate that RTS provides more accurate results than the traditional scheme. To investigate the effect of the aggregate morphology on particle aggregation and settling, basic fractal theory was incorporated into the settling velocity and collision frequency function expressions. A recently reported empirical expression relating these two parameters was used to investigate the effect of this connection on particle transport and aggregation. Simulations showed that both terms are important and any incorrect estimate of these parameters could compromise the reliability of the modeling results.; Adsorption and aggregation experiments were conducted on model systems using hematite as the solid phase, sodium chloride as the background electrolyte, and three different adsorbates (picolinic acid, pyromellitic acid, and lead). The triple layer model (TLM) for surface complexation satisfactorily modeled all the experimental adsorption data. The TLM parameters obtained from the fittings were used to study the effect of adsorption on the electrostatic properties of the hematite surface and to estimate surface potentials for different chemical scenarios. The surface potentials were used to calculate interparticle forces and particle stability. Stability factors derived from aggregation rates collected using dynamic light scattering (DLS) were consistent with the stability trends predicted. The results of this work indicate that the TLM description of the charge/potential relationships at the solid/aqueous interface provides useful information on particle stability.