Relative insignificance of mineral grain zeta potential to colloid transport in geochemically heterogeneous porous media

The role of zeta-(zeta)potential of mineral grains in the initial depositio n kinetics of colloidal particles in geochemically heterogeneous porous med ia is investigated. Colloid deposition experiments with colloidal silica pa rticles flowing through columns packed with chemically heterogeneous sand w ere carried out. Patchwise chemical heterogeneity was introduced to the gra nular porous medium by modifying the surface chemistry of a fraction of the quartz sand grains via reaction with aminosilane. Experimental initial col loid deposition rates and resulting collision efficiencies were compared to theoretical predictions based on the measured average zeta-potential of th e chemically heterogeneous sand. It is shown that colloid deposition kineti cs are controlled by the degree of patchwise chemical heterogeneity and tha t use of the measured zeta-potential of the granular porous medium in theor etical predictions leads to erroneous results.