Tailings are the mixture of clay, silt, sand, residual bitumen and water that remain after bitumen is extracted from the sand at oil sands mines. This watery waste stream is transported by pipeline and deposited in ponds where the majority of the solids — mostly sand — settle to the bottom. The remaining fluid — mostly clay, silt and water — flow to the middle of the pond and separate into a water cap on the top of the pond and a mature fine tailings (MFT) at the bottom of the pond. The water is available for reuse in the extraction process. The MFT does not settle into a material suitable for reclamation for many decades.
Suncor Energy has successfully developed a new process called TRO™ that more rapidly dewaters MFT. This reduces the time it takes to reclaim mature fine tailings and allows for the reduction of operating tailings ponds. Shell Canada is also using a technology, called Atmospheric Fines Drying (AFD), to speed the treatment of tailings and create a dry material that will allow for faster reclamation. Now, through COSIA, Shell and Suncor in conjunction with the other Tailings EPA members are collaborating to improve this technology cooperatively.
In both the TRO™ and AFD processes, MFT is mixed with a chemical commonly used in municipal water treatment facilities to help settle out solids. This polymer flocculant sticks to the clay particles in the MFT and causes them to bundle together, allowing the clay to be separated from the water.
The thickened MFT is then deposited in disposal areas specifically constructed for dewatering. The water that is released is returned to the tailings ponds where it can be reused in the bitumen extraction process. The resulting material can be reclaimed in the same location where it was dried or transported to another location for final reclamation.
Since this dewatering process occurs progressively, reclamation work can be carried out more rapidly. Currently, AFD and TRO operations treat a substantial amount of the fluid fine tails generated at oil sands mines.
Suncor success story
The implementation of TRO™ in 2010 was a substantial change in the way Suncor manages fluid tailings that led to the treatment of record volumes of fluid tailings in 2015. Since Suncor implemented TRO™, the company has been able to turn the corner and stop the increase of fluid tailings volumes on site. This is a great step forward and Suncor is building upon this success by looking for ways to increase treatment capacity, which would allow the company to progressively reduce the total amount of its untreated fluid tailings volumes.
AFD success story
Shell’s commercial-scale Atmospheric Fines Drying (AFD) field demonstration has demonstrated that AFD technology can make significant improvements to tailings drying time which can result in a fine tailings deposit which releases water and gains strength in weeks rather than decades. Since the initial demonstration project in 2010, AFD projects are now located at both the Muskeg River and Jackpine Mines.
Over the last two years Shell has been very pleased with the progress of the AFD programme and the pace at which it was delivered – moving from conception to delivery in less than a year. To date, over 1 million tonnes of fines have been captured at our Muskeg River Mine through this technology.
Suncor has shared its innovative process with other industry partners through the Oil Sands Tailings Consortium (OSTC) founded in 2010. The consortium has since transitioned into COSIA’s Tailings EPA. Shell Canada has pursued a very similar technique, called Atmospheric Fines Drying (AFD). Since the launch of the OSTC and COSIA, Shell and Suncor have been able to share the work behind these technologies, in pursuit of working together to accelerate developments and improvements in the technology further and faster. While COSIA oil sands mining companies have access to the technology, it is important to realize that the technology may not suit all mine plans. This is one of many approaches being pursued to reduce the volume of mature fine tailings.