The amount of water stored in oilsands tailings ponds north went down slightly in 2015 compared to 2014, while the volume of fluid tailings increased.
That’s an information highlight from the latest tailings status report from the Alberta Energy Regulator (AER), which was published to its website this week.
Tailings ponds are essential to the oilsands mining industry's water-based extraction process, the AER notes, as they act as both holding basins from which process water can be recycled and as settling basins where solids can be separated from tailings.
But the ponds occupy a large surface area and are a main concern of environmental groups opposed to oilsands development.
Tailings are a mixture of water, sand, silt, clay and residual bitumen. While the sand tends to settle out quite quickly, the AER explains, some of the smaller particles of clay and silt (also known as fines) tend to remain suspended in water, forming fluid tailings.
This is the material that presents the challenge to oilsands operators as without intervention it “can take decades to settle, and even then only to a consistency of soft mud.”
A number of different tailings treatment technologies are used at the oilsands industry’s five mining projects. Here’s a look at the AER data on how they performed in 2014-15, as well as what’s been worked on for the future.
There was a total of 1,134 million cubic meters of fluid tailings and 401.6 million cubic meters of water stored in the mineable oilsands region in 2015.
This is an increase of 58.8 million cubic meters from 2014 for fluid tailings, but a reduction of 6.8 million cubic meters for stored water.
Thin lift drying
The technology used to process the largest volume of tailings in 2015 was thin lift drying, which is used by both Suncor Energy and Shell Albian Sands.
The AER says that in thin lift drying, “fluid tailings are removed from the tailings ponds and mixed with a small amount of additives that bind the small particles in the fluid tailings together. The fluid tailings are then thinly spread over a sloped area. In good conditions, the fluid tailings are dried in a couple of weeks. Following drying, another layer, or ‘lift,’ is added.”
Known at Suncor as tailings reduction operation (TRO), thin lift drying is the only technology in use at the project. Albian Sands refers to its technology as atmospheric fines drying (AFD), and the project also uses composite tails, thickened tails and fluid fine tailings drying.
Suncor increased its TRO treatment in 2015 compared to 2014, to 14.8 million cubic meters from 11.7 million cubic meters.
Albian Sands reduced its AFD treatment over the same time period, from 3.9 million cubic meters in 2014 to 0.9 million cubic meters in 2015.
The use of centrifuge technology to treat oilsands tailings is fairly new but increasing, with volumes treated going up at both Syncrude and Shell Albian Sands between 2014 and 2015. In centrifugation, additive is added to fluid fine tailings, the water is spun out and the dewatered tailings are placed in a deposit, the AER says.
Syncrude treated 4.1 million cubic meters of tailings via centrifuge in 2015, up from 2.7 million cubic meters in 2014. Shell increased its centrifuged-treated volumes to 3.9 million cubic meters in 2015, up from 1.1 million cubic meters the previous year.
Shell Albian Sands also uses thickened tailings (TT), where inside a thickener vessel a small amount of flocculants are added to bind the small particles together; warm water released is sent back to extraction and the TT is placed in a deposit where more water may be released.
Shell increased its tailings volumes treated with TT in 2015 to 6.5 million cubic meters, up from 5.9 million cubic meters in 2014.
Composite tailings and nonsegregating tailings
Composite tailings (CT) and the similar nonsegregating tailings (NST) technology are used by Syncrude, Shell Albian Sands and Canadian Natural Resources Horizon.
In NST, TT is mixed with sand from the extraction plant, an additive is added and the mixture is placed in a deposit. The process is the same in CT, except the operator starts with untreated fluid tailings versus TT.
While CT-treated volumes dropped at Syncrude’s Mildred Lake Mine in 2015 over 2014, to 4.9 million cubic meters from 5.7 million cubic meters, CT treated at the project’s Aurora North Mine increased, to 10.9 million cubic meters from 5.0 million cubic meters.
Shell Albian Sands’ CT treatment went up from 0.3 million cubic meters to 1.3 million cubic meters over the period.
In 2014, Canadian Natural reported zero tailings volumes treated with NST, increasing to 7.7 million cubic meters in 2015.
Technology development in 2014-15
Some tailings technology development is a joint effort through the platform of Canada’s Oil Sands Innovation Alliance, the AER notes, while some activities are funded by the individual operators.
The AER says that in 2014-15 Suncor continued exploring opportunities to optimize the cost and performance of TRO, including tests to improve mixing performance and drying area utilization, as well as testing additives from different suppliers.
Suncor also tested centrifuge technology to treat its tailings, and continued a test of capping one of its legacy ponds with coke.
Syncrude has been testing an alternative fluid tailings treatment technology where fluid tailings is mixed with waste material that covers the oilsands that is removed before mining. “The mixture is stackable, and reclamation can start right after the placement,” the AER says.
Syncrude and Shell
The two centrifuge operators have been field testing columns (about three meters in diameter and ten meters deep) to understand long-term performance of centrifuge cake once it is placed.
The AER says Shell also tested Geotube technology, where fluid tailings is mixed with a small amount of additive and then the mixture is filled into bags to dewater. The company is also exploring capping options for tailings post-centrifuge.
Canadian Natural Resources
“CNRL technology development was focused more on laboratory-scale testing,” the AER says, including tests to see how NST can be improved.
“CNRL worked in cooperation with an academic institution to understand how fast the indigenous microbes in the fluid tailings can help the tailings become denser, and how the process can be accelerated. Finally, field testing was done onsite to try thin-lift drying technology.”