BACKGROUNDOil sand is an important unconventional oil and gas resource, which is composed of bitumen, solid particles (including coarse and fine particles) and water. The key to its development and utilization is to improve the extraction efficiency of bitumen. Solvent extraction technology is expected to replace the existing water-based extraction technology due to its high bitumen extraction efficiency and environmental friendliness. The high residue rate of solid particles in bitumen and low recovery efficiency of organic solvent in gangues are two main problems during solvent extraction, which is closely related to the composition, structure and surface properties of solid particles. Therefore, it is very important to understand the mineral composition and surface properties, especially hydrophilicity/hydrophobicity, of solid particles in oil sand. The oil sands in Inner Mongolia, China are characterized by abundant reserves and high oil content. At present, the mineral composition and hydrophilicity/hydrophobicity of solid particles in the oil sands in this area are not clear.

OBJECTIVESTo investigate the mineral composition and hydrophilicity/hydrophobicity of solid particles isolated from Inner Mongolia oil sands.

METHODSCyclohexane was adopted to separate the bitumen and solid particles from the oil sands. Fine particles and coarse particles were then separated using a 45μm standard sieve. The composition and structure of the particles were investigated by laser particle size analyzer, X-ray diffraction analyzer, specific surface area and porosity analyzer, Fourier transform infrared spectroscopy, organic element analyzer, scanning electron microscopy-energy dispersive X-ray spectrometry (SEM-EDX). The hydrophilicity/hydrophobicity of the particles was determined by film floatation and water vapor adsorption methods.

RESULTSThe contents of fine particles and coarse particles in the oil sands were 53.4% and 46.2%, respectively. The fine particles contained montmorillonite, kaolinite, illite, α-quartz and anorthite, while the coarse particles contained α-quartz and anorthite with minor kaolinite, illite and montmorillonite. The contents of bitumen and hydroxyl group in the fine particles were higher than those in the coarse particles. The mean critical surface tensions for fine particles and coarse particles were >47.62mN/m and >45.55mN/m, respectively, and the average water vapor adsorptions per unit area were 1.27mg/m² and 0.41mg/m², respectively, indicating that the coarse particles were more hydrophobic than the fine particles.

CONCLUSIONSRegarding the adverse effects of hydrophobic solid particles on the separation and extraction of oil sand bitumen and the recovery of organic solvents, it is necessary to pay attention to fine solid particles and strengthen the research on the influence of coarse solid particles.