CHEMICAL MOBILIZATION OF MICRON-SIZED PARTICLES IN SATURATED POROUS-MEDIA UNDER STEADY FLOW CONDITIONS

Many waterborne contaminants are particulate in nature or are associated with small particles or colloids. Thus, consideration of the mobility of colloids in porous media is necessary for an understanding of contaminant transport in groundwater. Immobilization of colloids in porous media has been studied extensively for water filtration applications, but the reverse process of mobilization is seldom considered. This study addresses the latter process. Theoretical treatment of the mobilization process in steady flow situations generally involves consideration of London-van der Waals attractive forces and electrical double-layer attractive or repulsive forces at the point of contact between media and particle surface. Laboratory sand columns were used to test the suitability of this approach with respect to observed mobilization under changing chemical conditions. Colloids deposited on the porous media surface were mobilized when exposed to lower ionic strength solution without disturbing the flow rate. Although results did not contradict theory qualitatively, further theoretical development is necessary to consider a broader range of surface forces likely to affect mobilization behavior. Flow rate dependence of mobilization is indicated and must be investigated further in order to understand its basis.