Sorption of crude oil from a non-aqueous phase onto silica: the in ̄uence of aqueous pH and wetting sequence

Sorption of crude oil by mineral surfaces may a€ect its ̄ow and recovery in porous media. Here, crude oil sorption from a toluene±heptane phase onto quartz and silica gel has been investigated both in the presence and absence of an aqueous phase, as a function of time, oil-to-sorbent ratio, pH, and wetting sequence. Steady-state is attained in roughly 24 h, with sorption following Freundlich isotherms. Maximum sorption capacity of initially dry quartz is roughly 2 mg oil per g; that of initially dry silica gel is greater than 8 mg per g. Sorption capacities of pre-wetted quartz and silica gel are approximately 0.5 and 0 mg oil per g, respectively. Aqueous pH only a€ects sorption by pre-wetted quartz, where sorption is greatest at pH 4, roughly 25% less at pH 7, and roughly 50% less at pH 2. The e€ect of pH and wetting sequence on oil sorption can be qualitatively described by calculating the electrostatic interaction energy between the mineral±water and oil±water interfaces. # 2000 Elsevier Science Ltd. All rights reserved.