Multiple roles of graphene nanoparticles (GNP) in microbubble flotation for crude oil recovery from sand

Known for their high oil adsorption, hydrophobic properties and easy manufacturing, graphene nanoparticles (GNP) have been vastly studied in various applications. This study aims to investigate the effects of adding GNP into the flotation process to enhance oil recovery efficiency from oil-contaminated sand. The oil removal efficiency was tested in a laboratory-scale flotation process against various parameters including pH, GNP concentration and temperature. A maximum oil recovery efficiency of 70.4% was achieved at the optimum operating conditions of pH 7, 0.1 wt% of GNP and system temperature of 80 °C. Coherently, zeta potential measurements of GNP and microbubble showed that optimum graphene-microbubble attachment would occur at pH 6 to 7. This suggests that there is a preferential GNP-microbubble attachment that encourages oil-GNP-microbubble attachment during flotation. Interfacial tension was at its lowest at 0.1 wt% of GNP where maximum oil recovery was recorded. The reduced interfacial tension enhances both oil-microbubble attachment and oil-sand separation. On a different note, an increase in GNP concentration showed minimal changes on the viscosity and pH of the GNP aqueous solution. This is especially beneficial during post-treatment of the sand, in which restoring the original sand pH is not required.