SURFACE CHEMICAL EFFECTS ON COLLOID STABILITY AND TRANSPORT THROUGH NATURAL POROUS-MEDIA

Surface chemical effects on colloidal stability and transport through porous media were investigated using laboratory column techniques. App roximately 100 nm diameter, spherical, iron oxide particles were synth esized as the mobile colloidal phase. The column packing material was retrieved from a sand and gravel aquifer on Cape Cod, MA. Previous stu dies have indicated enhanced stability and transport of iron oxide par ticles due to specific adsorption of some inorganic anions on the iron oxide surface. This phenomenon was further evaluated with an anionic surfactant, sodium dodecyl sulfate. Surfactants constitute a significa nt mass of the contaminant loading at the Cape Cod site and their pres ence may contribute to colloidal transport as a significant transport mechanism at the site. Other studies at the site have previously demon strated the occurrence of this transport mechanism for iron phosphate particles. Photon correlation spectroscopy, micro-electrophoretic mobi lity, and scanning electron microscopy were used to evaluate particle stability, mobility and size. Adsorption of negatively charged organic and inorganic species onto the surface of the iron oxide particles wa s shown to significantly enhance particle stability and transport thro ugh alterations of the electrokinetic properties of the particle surfa ce. Particle breakthrough generally occurred simultaneously with triti ated water, a conservative tracer. The extent of particle breakthrough was primarily dependent upon colloidal stability and surface charge.