Tailings ponds are an integral part of our water management system, as they help to reduce withdrawals from the Athabasca River. These facilities store tailings from the bitumen extraction process. As the tailings settle, water is released and then recycled back into plant operations. Over 85 per cent of our water needs are met through these facilities.
Tailings structures are highly engineered and managed for long-term integrity and safety. At the same time, significant resources and expertise are focused on reducing the volume of tailings and treating them to be used in constructing our reclamation landscape. Based on our current suite of technologies, Syncrude’s business plan expects all tailings areas will either have been reclaimed or will be undergoing reclamation within 10 years of the end of mining operations. No untreated fluid tailings will remain in our post-closure landscape.
What are tailings?
Tailings is the material that remains after bitumen is extracted from oil sand. It is a mixture of sand, silt, clay, water and residual hydrocarbon. Tailings are stored in in-pit or out-of-pit tailings placement areas. As this material is deposited, the coarser components settle rapidly and are used in the construction of sand beaches or other landforms. The remaining components form fluid fine tailings (FFT). Currently, the surface area of our fluid tailings is approximately 49 square kilometres.
Although the FFT material consolidates to 30 per cent solids by weight within a few years of deposition, further consolidation is slow. Therefore we use both mechanical and passive technologies to accelerate consolidation in order to obtain a soil substrate suitable for use in reclamation activities. In 2018, 9.1 million m3 of fluid fine tailings (FFT) were removed from settling basins and processed into reclamation material.
Dam integrity and monitoring
Syncrude’s tailings facilities are built according to strict government regulations and are monitored for integrity and seepage. The Alberta Energy Regulator (AER) further oversees the safety of our tailings ponds under the Water Act, Water (Ministerial) Regulation – Part 6 Dam and Canal Safety and Alberta Dam and Canal Safety Directive, and performs annual inspections and audits. We are also guided by the Lower Athabasca Region – Tailings Management Framework (TMF) and Directive 085: Fluid Tailings Management for Oil Sands Mining Projects which require operators like Syncrude to progressively treat and reclaim tailings.
A network of 167 groundwater observation wells are located across our operation, of which 124 monitor tailings seepage. Monitoring results are reported to the AER annually, as required by our operating approval. A series of interceptor ditches and sumps ensure any seepage or run-off water from rain or snow falling on the pond embankments is collected and pumped back into the pond.
Responsible tailings management is a key component of the Mining Association of Canada (MAC) Towards Sustainable Mining (TSM) initiative. As a member, Syncrude follows industry best practices in tailings dam safety and operation. Internal assessments are required annually, with an independent, external verification every three years. An external verification for the 2016 reporting year confirmed Syncrude to have a well-developed tailings management system, with comprehensive monitoring and external technical review practices.
Reduce and reclaim
To reclaim tailings, we’ve invested over $3 billion over the last decade to develop and deploy three main technologies: centrifuged tails, composite tailings (CT) and end-pit lakes. These technologies are incorporated into our tailings management plans for Mildred Lake and Aurora North. We have consistently met our regulatory commitments and continue to work with Canada’s Oil Sands Innovation Alliance, industry partners, academia and the scientific community on further solutions.
Centrifuge technology combines fluid fine tailings (FFT) with gypsum and flocculent, acting as process aids, in spinning vessels (centrifuges) to separate out the water from the FFT. The released water is recycled into plant operations and the dewatered clay material is used in reclamation and landform construction.
In our initial placement activities the clay product was dense and strong after about one year, following a freeze-thaw cycle, and is now being used to reclaim a former mined-out area at our Mildred Lake site. There are currently 18 centrifuges in operation. In 2018, 7.61 million m3 of FFT was treated using this technology. Monitoring and evaluation of deposit performance continues.
Composite Tailings (CT) technology combines FFT with gypsum and sand. Upon deposit in mined-out areas, the tailings release water and quickly settle. The area is then capped with sand and soil, enabling the development of landscapes that support forests and wetlands. CT is being used at both the Mildred Lake and Aurora North sites. In 2018, 1.49 million m3 of FFT was processed into CT.
At Mildred Lake, CT placement is being used to reclaim our former East Mine and the entire area is expected to be fully reclaimed by the mid-2020s. The 57-hectare Sandhill Fen wetland research watershed was constructed at the northwest end of this area. More information on reclamation of this former mine can be found in the Land section.
Research is underway to assess replacing gypsum in the CT process with a lime byproduct from our flue gas desulphurization (FGD) unit. Lime is a proven and effective tailings treatment aid and could be used to improve the CT and centrifuge processes.
End-pit lake technology is a common and successful practice used to reclaim mines in the global mining industry. At Syncrude, it involves adding a layer of water over FFT to form an aquatic environment in an empty mine pit. Syncrude has invested over 40 years of research to study this technology, with the industry’s first commercial-scale end-pit lake demonstration now underway in our former West Mine.
Focus areas for research and monitoring include water quality, impacts of the underlying FFT layer, performance of the littoral (shallow shoreline) zone, interaction of biological communities, consolidation of the tailings, development of the shoreline, and the establishment of plants and insects. A number of universities are assisting in the research, including the University of Toronto, McMaster University, University of Alberta, University of Calgary, University of British Columbia and the University of Saskatchewan.
An adaptive management approach is being used to steward the lake toward its closure objectives. To date, monitoring indicates good progress. For example, shoreline erosion and stability is occurring as expected. FFT consolidation is also as expected, at approximately 1 m of settlement per year since 2013, which has increased the depth of the water cap to about 10 metres. Oxygen saturation in the water has increased, water quality is improving, and naphthenic acids have declined in concentration. A wide variety of biological communities are also developing, including algae, aquatic plants, zooplankton and macroinvertebrates. Skimming, dredging and shoreline cleaning are underway to address the presence of residual bitumen. In addition, waterfowl deterrents continue to be in place throughout this demonstration period.
Tailings technology development
We are currently researching additional technologies that could be used to supplement existing tailings remediation methods. These include:
Accelerated dewatering is based on methods successfully used in the Florida phosphate industry where it is known as rim ditching. This technology mixes FFT with an organic flocculent, which is then placed in deep deposits. The flocculent is the same material used by municipal water treatment systems. Flocculent molecules wrap around the clay mineral particles in the FFT, forcing them to settle faster. Initial tests showed a reduction in FFT volume by 50 per cent in three to five years.
Field trials are underway to test new mixing techniques and the addition of gypsum. We expect this to result in more initial water release, higher initial solids content of the treated FFT, lower solids content in the released water, and more ultra-fines sequestered in the deposit. This would improve both the strength and stability of the deposit, and allow for faster soil capping and reclamation. A field trial began in 2018 to compare results using gypsum versus the lime byproduct from our FGD unit. Monitoring is ongoing and, if tests continue to prove successful, accelerated dewatering could be an energy- and cost-efficient addition to our tailings reclamation activities.
This method, studied since the late 1980s, mixes FFT with clay overburden to create a fully functional surface that can be walked or driven upon, and used for terrestrial reclamation. A small-scale demonstration pilot plant operated in 2014 and 2015, with a field prototype in operation in 2018. Deposit monitoring continues and results so far are promising. Research continues and a large-scale demonstration came on-line in 2019.
FFT CLAY TREATMENT
As it consolidates, FFT releases water at a very slow rate due to the strong affinity between clay surfaces and water. Lab-scale demonstrations in our research centre however have successfully enlarged the size of the clay particles and treated them so they repel – instead of attract – water. This could potentially provide an additional tailings treatment process. A field trial is underway.
Tailings co-deposition places two or more tailings products in a mined-out pit with limited to no intentional mixing. We have performed laboratory scale tests to study several different combinations of which, based on positive results so far, we are advancing the co-deposition of FFT and CT to a field pilot. The objective of the pilot will be to observe long-term performance and determine the applicability of the technology at a larger scale. If successful, the technology could add an alternative fluid tailings treatment technology that may accelerate reclamation and closure activities.
Collaborative research efforts
We operate one of the largest private sector research facilities in Western Canada and participate in Canada’s Oil Sands Innovation Alliance (COSIA). COSIA coordinates collaborative industry research and knowledge exchange among its members. Research work includes literature reviews, laboratory projects, pilot trials and large, field scale demonstration and commercialization programs. Click here.
|Fluid Tailings volumes (million m3)||469.6||476.3||501.2||502.1||514.6|
|Centrifuge Cake volume1 (million m3)||2.5||3.5||5.3||6.7||6.4|
|CT Beach deposit2 (million m3)||12.1||11.0||1.1||2.36||2.11|
|Fluid Tailings volumes (million m3)||113.0||127.9||131.2||136.8||133.3|
|CT Beach deposit2 (million m3)||13.2||21.7||25.1||5.1||5.9|
1 Volume of reclaimable treated fluid fine tailings (cake) material produced from centrifuge process, calculated using a combination of instrumentation and sampling data.
2 Volume of reclaimable treated fluid fine tailings (beach deposit) material produced from composite tails (CT) process, calculated assuming a dry density of 1.45 tonnes/m3.