COLLOID DEPOSITION DYNAMICS IN FLOW-THROUGH POROUS-MEDIA - ROLE OF ELECTROLYTE CONCENTRATION

The role of solution ionic strength and counterion valence in controlling the dynamic (transient) behavior of colloid deposition in granular porous media has been investigated. Packed-bed column experiments were conducted using two different suspensions of positively charged colloidal latex particles and negatively charged glass bead collectors. Variations in the concentration of an indifferent, 1:1 electrolyte solution are used to demonstrate an inverse logarithmic relationship between the average area of collector surface excluded (''blocked'') by deposited colloidal particles and solution ionic strength. Both electrolyte concentration and type influence the dynamics of particle deposition in porous media. A transition from declining deposition rate (''blocking'') to increasing deposition rate (''ripening'') is observed when the concentration of an electrolyte containing divalent counterions is gradually increased. Results from experiments involving irreversible, monolayer particle deposition are used to determine values of the maximum attainable surface coverage for spherical collectors. These values are unique to the collector geometry, flow conditions, and particle sizes used in the experiments. Implications of the results to colloidal transport and mobilization in subsurface aquatic environments are discussed.