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Featured Articles
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Sep 2008
| Source: Oilweek Magazine
| | | Taming the tailings
| | | Dead ducks notwithstanding, extensive research is underway to deal with oilsands tailings in a more efficient manner
| | | by Melanie Collison
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| It only stands to reason that like everything else about oilsands surface mining, the leftovers are big. Very big.
The mine pits are big, and once the 8 to 12 per cent of the contents that´s bitumen is extracted, what´s left is an even bigger quantity of salty formation water in tailings basins loaded with sand, silts, and clay and topped up with repeatedly recycled Athabasca River water. The whole mess is laced with residual bitumen, production chemicals, and minerals.
The surface area of all the tailings ponds and experimental lakes in Alberta´s oilsands region is estimated at 60 square kilometres, the volume at 720 million cubic metres. By comparison, Sylvan Lake holds about 412 million cubic metres.
The tailings ponds serve as holding basins for water being recycled as well as collection sites for material ultimately to be used in reclamation. The problem is that while the coarse sand settles quickly, the fine solids separate out only somewhat over two or three years and left alone, might never completely segregate. As a result, only 80 per cent of the water can be repeatedly drawn off and re-used.
That silt soup, the consistency of ketchup, is called mature fine tails. It has to be contained behind dikes, as there´s always a risk of the kind of fluid seepage occurring at Tar Island Dike, the original tailings containment structure alongside the first mine on the shore of the Athabasca River.
Process-affected water is accumulating along with the mud. "There´s about 1.5 barrels of mature fine tails to every barrel of bitumen production," says Randy Mikula, head of the emulsions and tailings group in the advanced separation technologies section of Natural Resources Canada´s CANMET Energy Technology Centre in Devon, Alberta.
CANMET and the University of Alberta have taken the lead in tailings research in recent years. Strong industry collaboration has faded since the days of the Fine Tailings Fundamentals Consortium that developed consolidated tailings, which Suncor Energy Inc. pioneered in the field in the 1990s to speed the reclamation process.
"The industry is moving a lot of material. If you triple the industry [as projected], you could imagine it´s a big volume and big area. There´s no question something has to be done about it and something will be done about it," Mikula says. He´s been in oilsands research for 20 years, improving first extraction efficiency then environmental factors.
The struggle with managing tailings and speeding reclamation activities is to release the water trapped by clay.
"We´re looking at all sorts of options for dry stackable tailings so you can recreate the original landform," Mikula says. "Then you can start talking about reclaiming the boreal forest. There are two reasons [the push for results] is really taking off-public perception, and the companies are running out of space. Between those two factors, everybody is interested in doing something about these fluid fine tails."
The Energy Resources Conservation Board is certainly interested. It released a "No More Mr. Nice Guy" tailings management policy in draft form at the end of June, following on the heels of the deaths of 500 ducks on the Syncrude Canada tailings pond in May. Its directive, Tailings Performance Criteria and Requirements for Oil Sands Mining Schemes, and background information are available at www.ercb.ca.
The directive sharpens accountability by means of industry-wide criteria for managing tailings and specific enforcement actions if targets are missed.
Tailings treatment comes down to surface and interfacial science, Mikula explains. Surface science is the physics and chemistry of surfaces-how the surface properties of bitumen and clay can be manipulated to enhance bitumen recovery. Recovery requires surfactants. The same process that helps get grease off dishes helps get oil off sand and clays.
Then to stack up the suspended clay platelets into a solid requires further chemical manipulation of the surface properties. Without manipulation, electrostatic charges, and residual bitumen prevent coagulation.
Ultimately, the aim is to dry the mature fine tailings somehow into stackable material that has the consistency of soil. Because it lacks nutrients, it will need to be covered with sand for drainage and the original soil horizons to support vegetation.
Dry, stackable tailings will not need to be diked, but will no longer be pumpable. Transporting the material to a reclamation site as substrate for a forest will require coordinating truck routes with mining truck routes.
"Nothing is easy in the oilsands because of the volume and tonnage of materials you´re working with," Mikula points out.
Rising oil prices have brought economic feasibility to research advances of years past. In 2000, CANMET demonstrated it could create dry stackable tails at an oilsands operation in Utah.
"Last year, Syncrude and Suncor did very brief trials to prove to themselves there´s something to it," Mikula says, and CANMET is now in the middle of a large-scale centrifuge pilot project for them on a Syncrude lease.
"This trial is to get a large deposit so the engineers can do some geotechnical testing to get a better handle on the economics," he explains. "Other experiments with simple drying after aggressive chemical treatments are looking very, very promising. They dabbled in these things 25 years ago; now those same costs are starting to look pretty reasonable."
Processes such as putting the clays through the spin dry cycle require either mechanical or chemical manipulation first.
To consolidate its tailings, Suncor adds gypsum, a byproduct of its flue gas system for scrubbing out sulphur. The gypsum interacts electrostatically with the clays and the weight of added sand squeezes out the water.
"But there´s any number of additives to get the process just right," Mikula says, "including organic polymers called flocculents that increase settling. "Shell Albian is going to use flocculents. They call it NST, non-segregating tailings. The chemical treatment, in which very long molecules stick to different clays and interact mechanically, is enhanced by the addition of sand." (Albian Sands Energy Inc., which runs the Muskeg River Mine, is owned 60 per cent by Royal Dutch Shell PLC, 20 per cent by Chevron Canada Ltd, and 20 per cent by Marathon Oil Corp.)
"At CNRL [Canadian Natural Resources Ltd.], we showed the same process can be achieved with CO2. They´ll start that this fall. Not only does it sequester the CO2 to a certain extent, it´s also [using] a waste produce because [CNRL´s] hydrogen plant produces high-purity CO2. The mechanism is pretty subtle. In a broad sense, it changes how the clays interact. CO2 results in very slight acidification that helps release calcium ions. The bottom line is it is also an electrostatic effect.
"The CO2 doesn´t seep out because it reacts chemically. You need 600 to 1,000 ppm for consolidated tailings, but to maximize the CO2 to sequester, you can triple it," Mikula says.
Whatever the process, the resulting dry stackable tailings have similar properties.
"One day reclamation will happen right after the mining in the same way they do with coal," Mikula says. "The oilsands industry is relatively young. Look at when the coal industry started, and the tailings issues and messes; there´s an evolution. There are pieces [of our vision] coming into place. [We´re solving] the volume and storage of fluid fine tails issues. At-face sand deposition leaves the sand right there, and there´s an economic driver because they don´t have to move it around. It´s the first step in reclaiming right behind the mine operation. There´s going to be some small operators, maybe in Canada or maybe in Utah-they´re more flexible because they´re small-where we´ll see it before we´ll see it in Athabasca."
"There are four or five things ready to move to the next research phase. You might use one or two, or more, options to create dry stackable tails. Operators have permission to bury fluid fine tails under water [called end-pit lakes], but that takes a lot of space and a lot of water."
Water experts, meanwhile, are examining the chemically complex fluids in tailings ponds.
"Most of my work has to do with oilsands process-affected water, chemicals, and potential biological effects," says George Dixon, University of Waterloo biology professor and a member of the Canadian Water Network, a national network of centres of water research excellence. For 15 years he has led a research project funded by Syncrude and Suncor, the Natural Sciences and Engineering Research Council of Canada (NSERC), Environment Canada, and now the Canadian Water Network.
Of primary concern are naphthenates, surfactants found in all heavy oil; polycyclic aromatic hydrocarbons (PAH), which occur in oil and as byproducts of burning fuel; and sulphate and sodium salinity, along with some metals.
The interaction between naphthenates and salts disturbed from the naturally salty soils and overburden is of particular interest, but "it´s a mixture of more than 300 types of chemicals," Dixon says. "We can´t really separate them out, so we´re always talking about a mixture." The PAHs tend to settle out with the fine sediments.
The team´s test sites include different types and ages of tailings and process water. A couple are already stocked with fish.
"We have looked at the evolution of the chemical structure and toxicity," Dixon says. "We´ve done some work in the laboratory and some on wetlands constructed on the leases. We´re now starting to work in the Athabasca River watershed."
Bitumen in the region is close to or at the surface. Knowing what is natural to the region sets the parameters for declaring when a constructed lake can be considered successful.
"The chemicals in the waste materials are exactly the same type occurring naturally in rivers and streams," Dixon says. "Some streams up there look like the bottom has been paved because water-soluble materials over years-a lot of years-are removed, and you´re left with the dense hydrocarbon product in the streambed."
Given concerns about fluid leaking out of the 40-year-old Tar Island Dike and reports of disease rates downstream in Fort Chipewyan, Dixon says the question that must be answered is whether pollutants are increasing in the water because of oilsands activity.
"No one releases effluent into the river; no waste has been dumped into the river," he points out.
Fellow Waterloo professor and Canadian Water Network expert James Barker has extensive experience analyzing surface water in the oilsands region. He sits on a review board regularly evaluating Suncor´s mine development and reclamation.
He says no aquatic impacts have ever been found from the Tar Island Dike seepage, so the thinking is it´s water used to build the dike that´s leaking, not process-affected water from behind the dike.
"We presume the seepage ends up in the Athabasca River, but have no evidence of that," he says.
The dike "came about because of novel work that was done to start the oilsands when the only way to get at the bitumen was to dig in from the river [bank]," Barker explains. "Great Canadian Oil Sands [the forerunner of Suncor] didn´t expect to have to store water, but couldn´t get the tailings to separate, so the dike grew from something that was supposed to be a few metres high to 60 metres high. You won´t find anyone starting a mine that way these days."
He adds, "It´s not a good example of what the industry does, but is a useful illustration of the processes and the challenges that can occur."
Barker sees the progress in managing tailings as particularly timely, given the soils around new projects.
"Most of the initial Syncrude and Suncor mines´ [surrounding] natural soil and glacial material is not very permeable, so escaping water wouldn´t move very fast in groundwater. New areas have surficial sandy material so there´s a potential [water] would move faster towards receptors."
Mikula welcomes benchmarks of progress that free up attention for conventional pollutants: sulphur dioxide polluting the air at Fort McMurray and around upgraders, solvents used for extraction, heavy metals, the lost bitumen.
"Our focus next is going to be on [volatile organic compound] solvents going into the process. Dry, stackable tails still need some science steps, but there´s enough science on the table to go ahead with confidence."
Toronto-based Titanium Corp. is freshly armed with a $3.5-million Energy Innovation Fund Grant from the Province of Alberta to advance research developed at its Regina pilot plant into recovering hydrocarbons, titanium, and zircon from tailings.
Calgary-based MinMiner Technologies Ltd. has been collaborating with Suncor, recovering bitumen and naphtha from tailings using solvent-coated polyethylene beads. The project, boosted by $1.15 million from Sustainable Development Technology Canada, could be followed by an in situ demonstration plant.
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