A new approach to determine the relative importance of DLVO and non-DLVO colloid retention mechanisms in porous media

Abstract

The DLVO (Derjaguin-Landau-Verwey-Overbeek) approach to predict colloid mobility in porous media is centered on solution ionic strength and physicochemical surface properties of colloids and solid matrix. However, several colloid retention mechanisms are not related to such interfacial properties, but instead to hydraulic features like flow regime and pore structure. We aimed to determine the relative importance of DLVO-related and non-DLVO-related retention mechanisms, which remains poorly understood. For that, we developed a conceptual approach based on previous research on organic matter-coated goethite (OMCG) colloid mobility in quartz sand. OMCG colloid retention by DLVO mechanisms was negligible at 0.0 mM ionic strength. Therefore, any retention at 0.0 mM can be assigned to non-DLVO retention. At increasing ionic strength, the amount of DLVO retention is rising, while the amount of non-DLVO retention is independent from ionic strength and thus remains constant. This allows for a differentiation between the two types of retention mechanisms. To test this conceptual approach, we conducted OMCG colloid breakthrough experiments at varying interfacial conditions (ionic strength: 0.0–5.53 mM) and hydraulic conditions (flow rate: 0.11 – 5.02 cm min−1). From sessile drop contact angles and zeta potentials, DLVO and extended DLVO (XDLVO) interactions including Lewis acid-base interactions were approximated. The results show that colloid retention was almost exclusively related to DLVO retention mechanisms, while retention by hydraulic factors was practically irrelevant. We conclude that our conceptual approach can be applied to determine the relative importance of colloid retention caused by DLVO and non-DLVO mechanisms for further colloid-solid matrix systems.