xtraction of bitumen from Athabasca oil sands in Alberta, Canada, represents one of the largest mining operations in the world. More E than half million tons of oil sands are processed daily (Hepler and Hsi, 1989; Kasperski, 1992) by Suncor Energy Inc. and Syncrude Canada, Ltd. using the Clark Hot Water Extraction (CHWE) Process (Hepler and Smith, 1994). In this process, mined oil sands are digested and aerated in a tumbler, with a small amount of caustic addition, at a slurry temperature about 75°C to 80°C. The elevated temperature and caustic are used to facilitate bitumen separation (liberation) from sand grains. The conditioned slurries are then fed to a primary separation vessel (PSV). The liberated bitumen droplets, mostly engulfing air bubbles, are floated to the top of the pulp, forming a bitumen-rich primary froth in the PSV. The middlings from the separation vessel are further processed in conventional mechanical flotation cells to recover the remaining bitumen. The tailings from the PSV and the flotation cells contain mainly coarse sands and mineral fines with small amount of fugitive fine bitumen droplets. Approximately one million cubic metres of tailings are discharged into a tailings pond daily.Handling such a large volume of tailings represents one of the major environmental challenges. In general, fine tailings, after segregation of coarse sands, take several years to consolidate to a solid content of about 30% by weight. The resulting sediment is called mature fine tailings (MFT). Further consolidation of the MFT to a trafficable surface, capable of supporting a productive soil layer would require hundreds of years. Compounded with continuous generation of new tailings, reclamation of tailings ponds becomes a major issue for further oil sands exploration. To reduce the areas for tailings disposal by rapid release of water for recycle to the extraction, a new tailings management scheme, called consolidate or composite tailings (CT) process, was developed at Syncrude Canada Ltd. and Suncor Energy Inc. In this new process, the addition of coarse sands and about 1 kg/m3 of gypsum to the MFT accelerated consolidation of the MFT to a solid content as high as 82% by weight within 30 days. The adoption of the process can potentially result in a bitumen extraction operation at near-zero waste discharge.However, the use of gypsum in the CT process is anticipated to increase the concentration of calcium and other associated ions in the recycle water to bitumen extraction. The negative impact of these ions on oil sands processability has been observed in both commercial operations and extensive laboratory tests using batch extraction unit (BEU) (Sanford and Seyer, 1979;Sanford, 1983; Smith and Schramm, 1992).Unfortunately, the exact reason(s) for such negative effect remains to be further explored. Lack of sensitive techniques and systematic studies, compounded with the complex nature of oil sands and their extraction systems, appears to be responsible for slow progress in this area.
674A novel approac...
