Influence of goethite colloid retention on the zeta potential of saturated porous media

The transport or retention behaviors of colloids in bulk soil have been studied extensively. However, little is known about the influence of colloid retention on the properties of bulk soil. With this aim, the variation of surface electrochemical properties of saturated porous quartz sands after retention of goethite colloids was investigated by comparing the difference in the zeta potentials of quartz grains, with or without the transport of colloids. And the zeta potentials of porous media were calculated from in situ streaming potential measurement. Our results indicate that the retention of goethite colloids changed the surface electrochemical properties of porous media significantly. With increasing transport time, more goethite colloids deposited on the surface of quartz grains and changed the zeta potential of porous media. There was a higher content of goethite colloids on the surface of quartz grains after transport of goethite colloids and, correspondingly, a more obvious variation in the zeta potential of quartz grains, if the supporting electrolyte contained monovalent ions, as compared to higher valent ions. Calculations based on DLVO (Derjaguin-Landau-Verwey-Overbeek) theory indicated that the main factor influencing the deposition of goethite colloids was the electrostatic attraction force between goethite colloids and quartz sands. Under the effect of the electrostatic attraction force, the zeta potential of porous media was changed by the deposition of goethite colloids on the surface of quartz grains. These findings will provide a useful reference for the understanding of the effect of microparticles on the surface electrochemical properties of bulk soil during migration processes.