Recovery of bitumen from oilsands: gelation of ultra-fine clay in the primary separation vessel

Abstract

The bulk of bitumen recovery from oilsands takes place via a flotation/settling process in the primary separation vessel (PSV). Under certain conditions, some oilsands slurries become non-segregating, i.e. both fines and coarse solids remain in suspension and little or no bitumen froth is generated. An ultra-fine (<0.3 μm) component of the oilsands fines fraction (<44 μm) is identified as having the potential to be the major contributor to the thickening (gelation), or sludging, phenomenon observed in some ores. In this work we determined the amounts of ultra-fines in oilsands from different depositional environments. Although a generally linear correlation exists between ultra-fines and fines or clay contents, some samples were found to have a disproportionately high ultra-fines contribution relative to other oilsands. Waste units, in particular, were found to be extremely rich in the ultra-fines and clay-sized fractions. We used a 2H NMR method to measure both the rate and degree of gelation of ultra-fines suspensions separated from oilsands. Sludging conditions are reached when the ultra-fines concentration is between about 1.5 and 2.0 w/w%. Measurement of ultra-fines gelation times showed them to be of the same order as slurry residence time in the PSV. Laboratory jar tests have demonstrated that poor segregation of oilsands components can be correlated with the gelation conditions determined by NMR measurements.