A Mechanistic Approach to Predicting Colloid Deposition onto Representative Aquifer Materials and Solution Chemistries in the Presence of an Energy Barrier

Abstract:

Despite several decades of research we lack a mechanistic theory to predict deposition in porous media in the presence of colloid-collector repulsion (unfavorable conditions). Recently, mechanistic models have been developed that incorporate nanoscale surface heterogeneity in colloid-collector interactions. Comparisons of simulations to experimental data allows backing out a representative heterogeneity for the surface, which to date has been reported only for silica. Colloid deposition onto a variety of representative aquifer materials expected to be unfavorable under environmental conditions (quartz, muscovite and albite) was observed for 0.25, 1.1 and 1.95 µm carboxylate-modified latex microspheres using an impinging jet system. Deposition efficiencies varied in response to changes in collector mineralogy, ionic strength, electrolyte valence and pH. Collector surface charge heterogeneity characteristics (heterodomain size and spatial distribution) were backed out from these experiments via comparison to particle trajectory simulations incorporating discrete nano-scale attractive domains (heterodomains). A bi-modal distribution (1:4, ratio of large to small heterodomains) of 120nm and 60nm heterodomains was found to quantitatively predict retention for all three colloid sizes for a given surface. Varying the surface coverage of heterodomains allowed a characteristic coverage for each observed collector surface to be determined. This developing catalog of surface characteristics will aid prediction of colloid transport and deposition under environmentally relevant conditions (aquifer material composition and groundwater chemistry).