Canadian Mining Journal

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Strict Rules

Suncor Energy Inc. has announced significant inroads with its Tailings Reduction Operations solution, while Syncrude Canada Ltd. has been testing centrifuge technology as one potential saviour. Smaller companies, such as Solid Environmental...



Suncor Energy Inc. has announced significant inroads with its Tailings Reduction Operations solution, while Syncrude Canada Ltd. has been testing centrifuge technology as one potential saviour. Smaller companies, such as Solid Environmental Services Ltd, Foret Plasma Labs, LLC and Micro-TES, Inc., remain on the sidelines heavily promoting their own solutions to the majors.

The massive waste water ponds – containing a slurry of water, clay, sand, silt and residual bitumen resulting from the Clark hot water extraction process – have become one of the industry’s biggest environmental and public relations challenges. Some 750 million cubic metres of mature fine tailings (MFT, consisting of fine clay particles suspended in water), have accumulated in fluid containment structures in the oilsands region.

Left alone, the fines are taking far longer than was originally estimated to settle out from the water – by some estimates it could take 500 to 1,000 years or more. Add to that Syncrude’s ongoing trial on charges relating to the deaths of 1606 ducks that landed on its Aurora settling basin in 2008, bolstered by more negative reports, such as recent details of the deaths of mammals from bears and wolves to deer and moose – and concerns over possible contamination of surrounding water bodies, and the recipe for a public relations headache persists.

The Alberta Energy Resources Conservation Board’s Directive 74, announced in February 2009, requires that oilsands mining companies convert at least 20% of the fine particles in their tailings ponds to solid waste by June 2011, rising to 50% by 2013 and annually thereafter. Tailings ponds must be ready for surface reclamation within five years of the ponds becoming inactive. Thus far, only Suncor has committed to meeting the directive’s deadlines, while at least one other company has submitted plans that won’t meet the new deadlines.

The inability of the majors to commit to meeting the deadlines is particularly irksome to those who believe they have the answer to the tailings problem, if only they could be given a chance to prove it.

Directive 74, designed to be the first component of a larger initiative to regulate tailings management, specifies performance criteria for the reduction of fluid tailings and the formation of trafficable deposits. It stipulates that within one year of the creation of a dedicated disposal area (DDA ), the area must attain a minimum undrained shear strength of five kilopascals (a unit of pressure measurement – one kilopascal corresponds to about one per cent of atmospheric pressure), rising to a minimum shear strength in five years of 10 kPa, trafficable and ready for reclamation.

While some companies have indicated that deadline may not be attainable with existing technology, Darryl Lasenby contends he has already demonstrated to the Alberta Research Council and the University of Alberta tailings pond research group that the figure is achievable. In fact, his company’s PitDry process can attain it within weeks, he says.

“We already have the equipment in place and material on hand to clearly demonstrate the process to the oilsands producers,” says the owner of Devon, Alberta-based Solid Environmental Services, which markets the Cetco Oilfield Services Company’s PitDry process in western Canada. “The whole problem with the tailings ponds is to reach that five kPa rating; that seems to be everybody’s hurdle. Within two weeks we were over the five kPa threshold, with just our baseline material.”

Composed of a powdered, inorganic mineral formula, the bentonite-based PitDry solidification process has multiple uses, including handling of drilling waste, mining and industrial waste treatment, lagoon remediation, and solidification of polychlorinated biphenyls (PCBs) and other polycyclic aromatic hydrocarbon (PAH ) waste streams.

Bentonite, formed by the alteration of volcanic ash deposited in the sedimentary environment, used with other proprietary components, rapidly absorbs the water and transfers liquid waste into a soft solid. It can take out so much water, 500-700% by weight of water, because the sodium cation is readily hydrated – water can enter its expandable sheet structures extremely easily. Its high water volume absorption capacity means only small amounts, usually two to five percent by weight, are needed to solidify wastes.

“We are adding bentonite under a high shear – a bentonite and a super absorbent polymer and some other materials,” explains Lasenby. “We blend them together, and then it becomes a solid matrix.”

Its high absorption capability promotes the binding and encapsulation of heavy metals and organic contaminates inside the solid matrix, so they will not leach out and cause environmental issues.

Sodium bentonite clay has a platelet structure resembling a deck of cards, according to the company. Due to its small dimensions, a cubic inch of bentonite clay powder is composed of an estimated 130 million platelets or particles. As a result the surface area is extremely high. When two to four per cent of sodium bentonite clay is dispersed under high shear into water, the clay platelets separate and form a house of cards with the surface of the exfoliated platelets fully exposed to water molecules, says the company. “The same one cubic inch of sodium bentonite powder would have an exfoliated surface area in water of about one acre or 43,000 square feet.”

“The last oilfield job we did, there was 1.1 million pounds of material on the ground that we processed,” Lasenby says. “We went from 1.1 million pounds to 350,000 pounds of material a week-and-a-half later, and they came in and hauled it all away to a landfill. That’s all they took away – Mother Nature grabbed the rest [through evaporation] for nothing.”

Lasenby has met with officials from Syncrude and the former Alberta Energy Research Institute and even his MLA, Doug Horner, Minister of Alberta Advanced Education and Technology, to little avail. Costs and the ability to handle such huge volumes as those represented by the tailings ponds appear to remain barriers. He says producers want to deal with their ponds at a cost as low as $3 or less per cubic metre, something he does not believe is attainable.

Lasenby says that while he knows any single technology isn’t the answer, “because every tailings pond mixture is different,” his company’s solution could be part of the mix. It could, for instance, be blended at smaller rates, and less cost, to existing processes to speed drying. “They [producers] are interested, but not at a cost. They seem to be looking for a magic pill that is absolutely free,” he says.

“Their comment is, ‘You guys couldn’t handle that much volume anyway,’ but do you not have to start with the first gallon before you deal with your tenth gallon? You have to start somewhere. Nobody is going to build a machine that can do a million gallons a day unless they know they can do one gallon a day.

“It’s not like we are two guys in a garage with a good idea. This is backed by a billion dollar corporation,” he notes. “The technology and the money to back it are there. I think the only way anybody is going to be able to understand it, see how it works, is to try a pilot. And I know Cetco would gladly go up and run things for a week, just to prove our process. But we need the opportunity to get a pilot.”

Suncor, meanwhile, appears to be putting all its marbles on its new Tailings Reduction Operations (TRO ), for which it allocated $450 million as part of its 2010 capital spending plans. Suncor, which pioneered the consolidated tailings (CT) process in the 1990s to speed consolidation of mature fine tailings (by adding sand and gypsum to accelerate dewatering), has been testing MFT drying, a key component of TRO, since 2003.

In the TRO process, MFT is mixed with a polymer flocculent and spread in thin layers on shallow sloped sand banks. The polymer flocculent adheres to the clay particles in the MFT,
causing them to bundle together, according to the company, separating the clay from the water. The released water evaporates or drains back into the settling pond for reuse.

Suncor says the flocculent is composed of an anionic polyacrylamide, an inert class of chemical used in municipal water treatment that does not react with the environment. The company has applied to implement TRO at its Millennium and North Steepbank/span expansion mines. Suncor says its use would bring about a reclaimable surface in 10 years after initial disturbance, compared to 30 years using the CT approach.

Syncrude has been, among other things, experimenting with centrifuge technology at its Mildred Lake operation. Though considered costly, centrifugal separators are a well established, heavy duty technology.

In MFT field trials, Syncrude operated two pods of oilfield scale centrifuges in parallel. Two Alfa Laval Lynx 40s were run to provide centrifuge cake for transport assessment (conveyor and positive displacement pump/pipeline studies) and bulk materials for geotechnical and environmental studies. And an M-I Swaco 518 centrifuge was used to advance MFT flocculation and MFT centrifuge process understanding.

Among the conclusions were that MFT centrifuge cake can be pumped, but it must be sheared first to reduce yield stress; that pipeline friction factors are relatively high but can be pumped via positive displacement pumps; and that when deposited, the material showed little water bleed – an advancing front is apparent with surface cracking, the company found. In a presentation in November, the company said it was investigating all cake transport alternatives – trucking with specialty boxes, pumping, conveying and possibly direct deposit from floating centrifuge barges for some in-pit deposition.

The company has also been investigating rim ditching, a technology borrowed from the phosphate industry in Florida in which a ditch is dug around polyacrylamide-strengthened MFT so that water can be drained off. The company estimates rim ditching can reduce MFT volumes up to 50% over a five-year period.

Canadian Natural Resources Limited said last fall it would not meet the ER CB deadline for fines capture in a DDA . But that’s not to say it has not pioneered some unique technological solutions at the newest oilsands mining project, which reached first production last year.

At its Horizon project, CNRL is mixing CO2 rather than gypsum as a coagulant with fine clays and silts in the tailings. The CO2, which will eventually come from CNRL’s upgrader, reacts to form carbonic acid, changing the pH and causing the fine clays and silts to more rapidly settle. Like gypsum, CO2 gives tailings fines sufficient strength to allow the courser sand to mix in with it rather than simply sink to the bottom. The sand can then supply the necessary pressure to force out the water. With the more rapid settling, the company can then recycle the water while it still retains some heat, reducing the amount of energy required to reheat the water while at the same time allowing for smaller tailings ponds.

As an alternative to meeting its ERCB deadline, CNRL is looking at two options that could allow it to surpass the annual target of 90% fines capture by 2015, and ultimately exceed cumulative fines capture requirements by 2025. One would be to implement non-segregated tails (NST) as soon as possible with a target 85% fines capture, combined with MFT dewatering using organic polymer and CO2 addition for 15% fines capture. The other option would see polymer and CO2 treated MFT dewatering expanded to capture greater than 50% of the fines while Pond 1 would operate as a conventional tailings pond with continued CO2 treatment of segregated tailings.

Imperial Oil Limited, meanwhile, is evaluating several fine tailings management technologies for its planned Kearl mining project scheduled for 2012. Among the options are early implementation of the consolidated tailings process, MFT thin lift drying/freeze thaw, MFT centrifuge and thickened tailings.

Shell Canada Limited spokesman Ed Greenberg says Shell supports the objectives of Directive 74 as it continues to work on tailings technology and collaborates with research institutions. “We are continuing to work with ERCB on specific details and timeline for compliance. In addition, Shell is advancing a number of options in an effort to meet the directive,” he says.

While not being specific about what technology the company will use to meet the directive’s timelines, Greenberg notes the company has invested $100 million in tailings research since 2005, including a state-of-the-art Tailings Test Facility at the Muskeg River Mine.

This special report was provided by Maurice Smith, Editor, New Technology Magazine, a sister publication of Canadian Mining Journal and published by June Warren-Nickel’s Energy Group, Calgary.


 

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