Tailings Ponds Up Close

Oilsands miners are making progress in their efforts to shrink their tailings ponds and are being prodded to quicken their pace by a regulator’s recent rules, say tailings technology researchers.

The Alberta Energy Resources Conservation Board’s Directive 74 makes it clear that operators need to accelerate their pace at developing tailings technologies and they are working together to do that, says Alan Fair, chairperson of the tailings consortium within the Canadian Oilsands Network for Research and Development. CONRAD is a network of companies, universities and government agencies organized to facilitate collaborative research in science and technology for Alberta’s oilsands.

“I’d like to say that the industry would have done that anyway but the reality is that there’s no question the industry has been called to task here a bit, and has responded,” said Fair.

The directive, Tailings Performance Criteria and Requirements for Oil Sands Mining Schemes, was released last February and applies to all mineable oilsands operations. It requires the reduction of fluid tailings, their capture in ERCB-approved dedicated disposal areas (DDAs) and their conversion to trafficable deposits which means they can be walked upon and bear the weight of heavy equipment.

Tailings are a mixture of water, clay, sand and residual bitumen that result from oilsands mining. They are stored in large ponds where the clay/water mixture is left to settle. Tailings ponds cover about 130 square kilometres of the oilsands region.

Facilitated by CONRAD, Directive 74 has led to more collaboration within the industry, said Fair.

CONRAD’s tailings consortium has representation from the four existing oilsands operators (Suncor Energy Inc., Syncrude Canada Ltd., Shell Canada Limited and Canadian Natural Resources Limited (CNRL) as well as three companies with proposed projects: Total E&P Canada Ltd., Imperial Oil Limited and Petro-Canada.

“None of the existing owners are adverse to the development and implementation of the tailings directive. I think everyone recognizes and agrees that there’s a need to put more focus on managing the tailings challenges,” said Fair.

Both the owners and the ERCB acknowledge that one of the areas that needs work is in the measurement parameters, he said.

For example, the directive requires that within one year of the creation of a DDA, the area must measure five kilopascals (a kilopascal is a unit of strength) and that may be impossible to achieve, depending on the chosen technology, said Fair.

Industry and the ERCB are working together to come up with a solution, he said.

Directive 74 has stirred up a “huge response” among mine operators, but in all fairness operators had been working diligently to curb tailings long before the ERCB’s announcement, said Dr. Randy Mikula, a tailings pond research scientist. The head of emulsions and tailings at Natural Resources Canada (NRC), he has spent more than 20 years researching oilsands processing from extraction to tailings behaviour and now specializes in reducing the environmental impact of surface mining.

Both Fair and Mikula agreed that the technologies that work best will be project-specific. There is “a whole pile of things on the table,” and the tailings technologies that will become the companies’ “best” treatments will depend on their projects, said Mikula. While some companies might apply three or four different technologies, others might be able to get away with only one or two, depending on their operation, he said.

Technologies in that “pile on the table” include water capping, centrifugation, composite tails, MFT (mature fine tails) drying, accelerated dewatering and the use of carbon dioxide.

Syncrude is experimenting with three main methods: water capping, composite tails and centrifuge. Taking a multi-pronged approach, it is also researching other technologies. “We feel that it will take more than one,” said Cheryl Robb, media relations advisor.

In water capping, a layer of water covers a deposit of fine tails, forming a lake. Syncrude says tests have shown these lakes will evolve into natural ecosystems and after the final deposition of fine tailings, eventually support healthy plants, animals and fish.

Composite tails combines fine tails with gypsum and sand, causing the tailings to settle faster than they would on their own, thereby speeding up the process of developing landscapes of grass, trees and wetlands. Syncrude will implement water-capping and tails on a commercial scale in the east-and west-end pits within the next five years, said Robb.

Centrifuge, spinning out water from the fine tails, has been piloted twice in the past two years and research is ongoing. It’s fast but costly, said Fair, who also manages Syncrude’s research and development department.

Mikula is a big fan of centrifuge technology. “It’s not going to be for everyone and to be honest it still needs some work, but that work’s progressing very, very quickly and so far everything looks pretty promising,” he said.

Syncrude is taking the lead on that technology and is sharing what it learns with its competition. The competitive advantage is in the operational experience, not necessarily in the know-how, he added.

The fourth technology that Syncrude is researching; thickened tails, or paste technology, is also promising to speed up the settling process. Tailings sent out to the pond are first sent through a product separating vessel to thicken the mixture. The fine solids settle out rapidly and are pumped out as a viscous fluid with a paste-like consistency. This soft clay will be immediately used for reclamation into a finished landscape.

Shell has commissioned a $100-million tailings pilot plant at its Muskeg River mine to produce trafficable tailings. The company is experimenting with various tailings technologies to identify the best mix of solid particles and techniques for increasing water recovery and creating dry tailings.

Its current tailings management plan is designed to remove all water and then blend and treat the remaining solid tailings.

Shell has demonstrated tailings management options such as non-segregating tailings and paste tailings technologies and has been running a pilot project since 2007. It is gathering information for the design of large-scale facilities and deposits, said spokesperson Phil Vircoe.

Starting this year, the company will be placing the first tailings material in the mined-out pit areas.

The newest oilsands mine, Canadian Natural Resources Limited’s Horizon, injects waste CO₂ into the tailings slurry lines before the tailings enter a pond, where the carbon dioxide reacts to form carbonic acid. This reaction changes the pH of the tailings mixtures and allows the fines clays, silts and sand to settle quickly and leave clearer water which can be immediately recycled for reuse in the bitumen extraction process.

CNRL plans to implement another new tailings treatment process during Horizon’s next phase. As part of this new process, cyclones will remove the water from the coarse sand, and thickeners will remove the water from the fine clays, silts and sand. The dewatered streams will then be combined with waste CO₂ . The tailings that result will be deposited in the tailings disposal area where even more water will be released and reused.

Additionally, the CO₂ will react with the minerals in the tailings to form mineral carbonates. In this phase, the waste CO₂ will be captured from Horizon’s upgrader instead of being purchased and trucked to site.

“CNRL is doing something really cool,” said Mikula. “The beauty of CO₂ is it actually gives you a water chemistry that’s beneficial to the extraction process so you don’t have to worry about over-adding your process aid.”

CO₂ chemically works on the fluid fine tails in the same way that gypsum does to create consolidated
or non-segregated tailings, using mature fine tailings (MFT) in the recipe, he said. “And what’s interesting with that, of course, is CO₂ is a big environmental issue so you get to take some credit for the CO₂ that you sequester in the tailings.”

The trouble is, eventually those bubbles are going to find their way to the surface so with the current process CNRL won’t be able to get the CO₂ credits. Mikula and NRCan are working on that, though. The trick is to get the chemistry and physics of it just right so that the bubbles are small enough that they will react before they coalesce and get big enough to bubble out, he said.

In the same way that gypsum does, CO₂ gives tailings enough strength so that the sand will mix in with them, said Mikula. “There’s a recipe involved. You need the mature fine tails or the fluid fine tails which has clays and silt -very, very fluid material. If you throw sand in it, the sand will just go to the bottom and you won’t really achieve anything. But if you get the chemistry just right, that fluid fine tails has enough strength to hold the sand, and then the sand is supplying pressure that squeezes water out; and because you’ve squeezed water out, now you’ve got something you can walk on, whereas before, it was too fluid, it would have had to have been behind a dike.”

These new processes are designed to reduce the footprint of the tailings pond, and by increasing the amount of water available for recycling, decrease the amount of river water needed to process bitumen. CNRL also expects the process of sequestering CO₂ into tailings will eliminate about 219,000 tonnes.

Suncor, which recently planted the first trees on what will be the first tailings pond reclaimed by the oilsands industry, has made tremendous strides in reclamation, said Mikula. “It’s very, very impressive.”

It’s one of the many steps the company has taken towards bringing Pond 1, its 40-year-old tailings pond, back to the original state, said Shawn Davis, Suncor spokesperson. “Once that is achieved it will be a major milestone not just for Suncor but for the industry,” said Davis.

Suncor stopped putting its tailings into the roughly two-square-kilometre area about 10 years ago and it is now almost completely “trafficable,” meaning it can be walked upon and bear the weight of heavy equipment. If all goes well, the final state will be a mixed-wood forest and a small wetland capable of supporting a variety of plants and wildlife.

The company is on track to live up to its commitment of reclaiming it by 2010, said Davis. To get to that goal, Suncor has been moving the soft mature fine tailings and water to ponds that are better suited to their long-term treatment, and replacing them with sand from the extraction process, she said. The sand’s surface was then molded into hills and valleys that promote plant and animal habitat before it was capped with the material that was saved from when the area was dug up.

Industry researchers also are collaborating on a method of injecting flue gases such as CO₂ into tailings ponds to feed the growth of micro-algae which can then be processed into products like ethanol, biodiesel and fertilizer.

Operators have until Sept. 30 to submit to the ERCB their plans for meeting the new requirements. Annual tailings management plans for the next calendar year must be submitted by Sept. 30 each year thereafter. Requirements will be phased in and adapted, as approved by the board, to take account of particular mining and tailings plans, facilities and the status of a project.

In addition, the mass of fines -mineral solids -must be reported annually and quarterly.

However, no matter what companies do it won’t be fast enough for some people, Fair acknowledged. However, “you have to be realistic and at the end of the day you do what you can do.”

*This Report was written by Lynda Harrison, a Writer with New Technology Magazine, a JuneWarren-Nickel’s Publication and sister magazine to Canadian Mining Journal.