ABSTRACT
In Alberta, oil sands bitumen is utilized for synthetic crude oil production by surface mining, water slurry based bitumen extraction followed by bitumen upgrading processes. Oil sands tailings composed of water, sands, silt, clay and residual bitumen, is produced as a byproduct of the extraction process. Oil sands tailings produced by hot water and low temperature extraction processes are of different characteristics. Oil sands tailings, regardless of the type of extraction process used in the front end of the plant, has to be handled for the protection of the environment as well as for the recovery of the warm process water trapped in the tailings. Development of Composite Tailings technology made it possible to produce an engineered nonsegregating tailings product by blending cyclone underflow and mature fine tailings accumulated from more than twenty years of tailings deposition. Gypsum is used in this process as a chemical additive for bonding clay and sand particles together, however, the accumulation of Ca 2+ in the release water could be a long term concern for the recycle of the release water in the extraction process. Recent developments made in Paste Technology recovers about 70% of the water from the cyclone overflow by using polymeric flocculent and thickeners. Since then, production of another engineered tailings product is targeted, similar to Composite Tailings, by blending the cyclone underflow and the thickener underflow from the Paste Technology. This new tailings product is called Blended Composite Tailings. The objective of all of these processes is to change the tailings from a slurry to a low water content material that can be disposed of in the mine pits. The elimination of tailings ponds and the improvement of the release water chemistry are fundamental to lessen the environmental impact of the tailings and allow it to be reclaimed more economically and efficiently.
