Effects of mineral surface silanization and bitumen coating on its filtration from an aqueous slurry

Abstract

The effects of residual bitumen on oil sands tailings filtration have rarely been examined. In the present work, the filtration of bitumen-coated minerals, including quartz, rutile, kaolinite, and montmorillonite, was studied. Bitumen-coated quartz was compared with silanized quartz to decouple the effects of surface hydrophobicity and adsorbed bitumen layer on filtration. The minerals were treated in bitumen-toluene solutions with different bitumen concentrations. The treated minerals were subjected to vaccum filtration and their wettability was measured by sessile drop contact angle method. It was found that the filtration rate of silanized quartz was linearly correlated with contact angle. It was also observed that at low bitumen concentration, the contact angle and filtration rate of all tested minerals were increased. However, at high bitumen concentration, the filtration rates were reduced drastically despite the high contact angle. CHNS elemental analyses, and X-ray photoelectron spectroscopy surface composition and depth profile analyses showed that the minerals had higher C, N, S contents and thicker bitumen layer when they were treated at higher bitumen concentration. It was hypothesized that under the pressure gradient during filtration, the thick and patchy bitumen coating layers could inter-penetrate when the mineral particles were pushed together, to form a inter-locked film to close off the pores in the filter cake. Indeed, mineral-bitumen aggregates were observed by X-ray microscope/nanoCT imaging of the filter cake. It was concluded that a thin layer of bitumen coating helped filtration due to the induced hydrophobicity, but a thick (and patchy) bitumen coating impeded filtration.