Interaction between hydrocarbon oil and hydrophilic mineral surfaces: A chemical force microscopy and molecular dynamics simulation study

Hydrocarbon oil collectors are typically used in the mineral flotation process to increase the hydrophobicity of the mineral surface. However, the mechanism of action of hydrocarbon oil on hydrophilic mineral surfaces remains unclear. This study innovatively applied chemical force microscopy (CFM) and molecular dynamics (MD) simulations to study the interactions between hydrocarbon oil and hydrophilic mineral surfaces. The CFM results showed that the interactions between RCH3, ROH, RCOOH, and RNH4+ and the hydrophilic mineral surface are always repulsive, and can be well described by Derjaguin-Landau-Verwey-Overbeek theory, which considers both van der Waals and electrostatic forces. The type of functional group significantly influenced the adhesion force between the hydrocarbon oil collector and hydrophilic mineral surface, and the adhesion forces followed the order RNH4+ > ROH > RCOOH > RCH3, indicating that polar hydrocarbon oil molecules adhered strongly to the hydrophilic mineral surface, whereas nonpolar hydrocarbon oil molecules did not adhere to this surface. MD simulation results showed that polar micro-oil droplets easily spread on the hydrophilic surface, while nonpolar micro-oil droplets were difficult to spread. Hydrophilic mineral surfaces preferentially attract water molecules and repel hydrophobic hydrocarbon oils, which reduces the adsorption energy of nonpolar hydrocarbon oils. Polar hydrocarbon oil is an effective collector for increasing the surface hydrophobicity of hydrophilic minerals. The combination of MD and CFM illustrated the mechanism of action of hydrocarbon oil collector molecules, which provides a theoretical reference for mineral flotation separation.