(411b) Alternatives to Tailings Ponds for Oil Sand Tailings Disposal
Oil sand resources are playing an increasingly important role in maintaining energy supplies for North America. Bitumen is produced from oil sand, mainly by two processes: in situ recovery by SAGD (steam assisted gravity drainage) for deep reservoirs and open-pit mining operations for shallow deposits. In open-pit mining operations, bitumen is separated from sand grains by a hot-water extraction and flotation process that produces large volumes of tailings. In the existing commercial plants, tailings from the extraction operation are pumped into large settling ponds. The coarse solids settle out quickly as a sand beach while the fine particles settle very slowly and finally form mature fine tailings (MFT), a stable suspension containing about 30% solids. Over the years, large volumes of MFT have accumulated in the ponds and the continuing accumulation is a cause of growing economic and environmental concern.
In order to address these concerns we are actively investigating alternative methods of dry and stackable tailings disposal such as flocculation and thickening, filtration, and centrifugation. Coarse oil sand tailings are flocculated using polymeric flocculants and the sediments are either disposed in the mined-out pit or further filtered. Various factors affecting flocculation and filtration performance were investigated in this work. The results demonstrate that the tailings have much better filterability after appropriate flocculation, and filtration becomes a viable method of producing stackable tailings. Another method for treating fine tailings and MFT is centrifugation. Centrifugal force enhances the separation of fine clays from water and speeds up further consolidation. Pilot-scale test results show that centrifugation of the fine tailings produces consolidated cake that can be disposed of without the need for pond containment. These methods provide potential alternatives for eliminating or reducing the use of tailings ponds and for the recovery of water and the associated thermal energy.