Thermodynamic stability of the meniscus oil film between air/solid/water and its relevance to flotation

The behavior of oil is an important aspect in the area of mineral flotation or oil-water separation. This paper proposes a specific phenomenon that a meniscus oil film may form between the air bubble and the solid surface under water surroundings. A thermodynamic system containing an air bubble, an oil droplet, a solid matrix, and water surroundings was constructed. The mechanical equilibrium state of the oil meniscus film was solved. The free energy difference Delta B between the oil film-formed state and a reference state based on the Gibbs surface thermodynamic theory is applied to characterize the stability of the meniscus oil film. The impacts of the oil-gas volume ratio and the interfacial tensions are taken into consideration. The results show that the equilibrium morphologies of the system are directly correlated with the interfacial tensions. A minimal Delta Bmin can be found at a certain volume ratio and the case Delta B<0 generally exists. It indicates the formation of oil film leads the system to a lower energy state which is thermodynamically stable. The batch flotation using glass beads and n-alkane collectors was conducted. The flotation results show that the oil can improve the particle recovery and the results can be well interpreted by the mechanism correlated to meniscus oil film.