Role of spatial distribution of porous medium surface charge heterogeneity in colloid transport

The role of spatial distribution of porous medium patchwise chemical (charge) heterogeneity in colloid transport in packed bed columns is investigated. Colloid transport experiments with carboxyl latex particles flowing through columns packed with chemically heterogeneous sand grains were carried out. Patchwise chemical heterogeneity was introduced to the granular porous medium by modifying the surface chemistry of a fraction of the quartz sand grains via reaction with aminosilane. Colloid transport experiments at various degrees of patchwise charge heterogeneity and several spatial distributions of heterogeneity were conducted at different flow rates and background electrolyte concentrations. Colloid deposition rate coefficients were determined from analysis of particle breakthrough curves as a response to short-pulse colloid injections to the column inlet. Experimental colloid deposition rate coefficients compared well with theoretical predictions based on a colloid transport model that incorporates patchwise chemical heterogeneity. The results revealed the particle deposition rate and transport behavior to be independent of the spatial distribution of porous medium chemical heterogeneity. It is the mean value of chemical heterogeneity rather than its distribution that governs the colloid transport behavior in packed columns.