Oil Sands Miners Advance New Technologies for Tailings Management
Producers are moving to commercial-scale projects after years of pilot-scale testing
By Russell A. Carter, Managing Editor
The most familiar end product from the mining and processing sequence— synthetic crude oil—is quickly pro-cessed and shipped via pipeline to refineries across North America for con-version into commercially useful petro-leum products. The other end prod-uct—huge volumes of tailings—remains on site and has generally been stored in ponds or mined-out pits. Over several decades of oil sands mining, producers have tried a number of methods, such as cyclone separation, gypsum addi-tives and flocculant treatments, to reduce the time it takes for suspended fine tailings particles to consolidate to a level that would allow reclamation of storage facilities to begin—a process that normally takes decades, leading to an ongoing need for extended tailings storage facilities.
Although these ponds have been managed and monitored, their extent— estimated at about 170 km2 of surface area in 2010 by the Canadian Associa-tion of Petroleum Producers, containing more than 220 billion gallons of tailings fluids—and toxic ingredients have been contentious issues involving the produc-ers, regulators and the public at large.
The intensity of concern was ampli-fied in 2008, when an estimated 1,600 migrating ducks were found dead in a Syncrude Canada-owned tailings pond, trapped in sludge floating on the sur-face after landing in an area in which the company’s bird-deterrent systems had failed. A year later, Alberta’s Energy Resources Conservation Board (ERCB) issued Directive 74, which mandated new industry-wide criteria for tailings management and annual reporting on modified tailings plans.
The directive set out new require-ments for the regulation of tailings operations associated with mineable oil sands. It specified performance criteria for the reduction of fluid tailings and the formation of ‘trafficable’ (capable of supporting the equipment and traffic necessary to incorporate the tailings into a dry reclaimed landscape) de-posits. These criteria, according to the directive’s preamble, “are required to ensure that the ERCB can hold mine-able oil sands operators accountable for tailings management.”
To comply with the directive, pro-ducers are required to make submis-sions to the ERCB on how they will meet the new requirements and identi-fy any project-specific constraints that may have a bearing on meeting the requirements. “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,” according to the directive, and “the ERCB recog-nizes that fluid tailings management is developing and that operators may need flexibility to apply technologies and techniques that best suit the circum-stances of particular projects. The ERCB will consider submissions of operators and will determine project-specific requirements related to the directive.” Under the directive, produc-ers must regularly report their up-dated tailings management perform-ance to the board, compared with their approved tailings plans.
In response, oil sands producers Canadian Natural Resources, Imperial Oil, Shell Canada, Suncor Energy, Syncrude Canada, Teck Resources and Total E&P Canada established the Oil Sands Tailings Consortium in late 2010, described at the time as a uni-fied effort to advance tailings manage-ment by making tailings-related techni-cal information more broadly available to interested parties and eliminating financial and intellectual-property road-blocks that might prevent tailings management advances.
More recently, in March 2012, a larg-er group of oil sands producers formed a new alliance called Canada’s Oil Sands Innovation Alliance (COSIA), dedicated to “accelerate the pace of improving environmental performance in Canada’s oil sands.” Chief executive officers of 12 companies—including five of the six OSTC members, plus BP Canada Energy, Cenovus Energy, ConocoPhillips Canada Resources, Devon Canada, Nexen and Statoil—signed the alliance’s founding charter, which commits the organization to establish structures and processes through which members can identify, develop and apply solutions-oriented innovation to oil sands environmental challenges, specifically water, land, greenhouse gases and tailings. (Syncrude Canada, a member of the OSTC, did not initially join COSIA but has been engaged in talks regarding pos-sible membership.)
Reading the Roadmaps
The various alliances appear to have begun bearing fruit: In August 2012, out-comes from the Tailings Technology Roadmap and Action Plan project— another collaboration, this one involving the provincial corporation ‘Alberta Innovates—Energy and Environment Solutions [AI-EES]’ and the OSTC in part-nership with Alberta Energy, Natural Resources Canada, Alberta Environment and Sustainable Resource Development, and the Alberta Energy Resources Conservation Board—were released to the public and described as a “comprehen-sive review of technologies that will help industry identify the suite of technologies that are best for their operations.”
The roadmaps presented in this report focused mostly on tailings pro-cessing, tailings deposition and cap-ping technologies. Suncor, for example, had completed more than $1 billion of infrastructure realignment work between 2010–2012 to implement its TRO (Tailings Reduction Operations) process, a technology it has been test-ing since 2003 that it says will allow the company to convert mine tailings into a material solid enough to be reclaimed in a fraction of the time that earlier technologies require. With this new drying process in place, according to Suncor, it expects to reduce the time it takes from initial land disturbance to having a reclaimable surface to about 10 years—a third of what is now the industry standard.
Implementation of TRO-based tailings treatment, said the company, has enabled it to cancel plans for five addi-tional tailings ponds, and Suncor expects it will be able to reduce the number of tailings ponds at its current mine site from eight to one. The first phase of the tailings-infrastructure projects to implement the TRO process was completed in the first quarter of 2012, with the second phase slated for completion by year-end 2012, and advancement of the TRO process toward full commercial scale operations is well under way with six systems operational, and a seventh under construction, Suncor reported.
Zulfiqar Ali, senior engineer–tailings planning at Suncor, described the TRO approach in a paper presented at the Tailings and Mine Waste 2011 conference held in Vancouver, B.C. The implementation of TRO is based on two primary technologies: mature fine tailings (MFT) drying; and sequential con-struction of sand dumps. MFT is the classification for fine clay particles, smaller than 44 microns, suspended in water; it is the most challenging com-ponent of oil sands tailings when it comes to finding solutions that accelerate particle settling time.
In the TRO process, MFT is mixed with a polymer flocculent, then deposit-ed in thin layers over sand beaches with shallow slopes. The eventual product is a dry material that is capable of being reclaimed in place or moved to another location for final reclamation. This dry-ing process occurs over a matter of weeks, allowing for more rapid reclama-tion activities to occur.
Under the TRO scheme, process tailings will be deposited into in-pit beach-ing areas enclosed by berm structures where sand will trap portions of the fine tailings while the remaining fines will be suspended in water in the form of thin fine tailings. The thin fine tailings will then be transferred to MFT settling ponds where they will receive a polymer additive in the MFT drying process.
The tailings with polymer additive will then be deposited in thin layers over sloped beach areas, where freeze/thaw processes and the polymer treatment will then help recover a por-tion of the water, while the remaining water will evaporate or remain in the resulting deposit. The end result is a clay product that can be reclaimed in place or be placed in mine dumps.
Suncor reportedly spent $250 million to develop the process and although it has, and will continue, to spend millions to construct the estimated 500–600 hectares of beaching areas needed for drying tailings, it figures it will save at least $1 billion over the next decade by using this approach to reduce its need for future conventional tailings ponds. Suncor has patented the TRO process and says it is willing to make the tech-nology available to other interested par-ties—a step that hasn’t yet taken place.
“What we’re [asking] is, we want to help recoup our R&D costs,” Suncor CEO Rick George told the Toronto Globe & Mail in a recent interview. “That’s a reasonable request.”
Capping it Off
Syncrude Canada, the largest oil sands producer, is moving ahead with several tailings management technologies, which include centrifugation of MFT and water capping among others.
Syncrude plans to implement cen-trifuging technology in two stages: a first-stage, commercial-scale plant that, at last report, was scheduled to come online by the end of 2012, and a $1.9-billion full-scale plant that will start up in 2015. In November 2012, it awarded Houston, Texas, USA-based engineering company KBR two con-tracts to execute module fabrication and field construction for what it calls its Fluid Fine Tailings—Centrifuging Full Scale Plant (FFT-CFSP) in Fort McMurray, Alberta.
KBR Canada subsidiary, KBR Indus-trial Canada, will provide module fabri-cation and construction services for FFT-CFSP. Module fabrication is scheduled to begin late this year and run through the end of 2013. Construction will fol-low with mechanical completion sched-uled to allow plant start-up in 2015.
Syncrude’s centrifugation method is a two-step process. The first step involves MFT dewatering using horizon-tal solid-bowl scroll centrifuge technol-ogy with flocculent addition, forming two streams: relatively solids-free water having 0.5% to 1% wt solids, that can be returned to the water system for recycle; and cake, a soft soil material capturing greater than 95% of the solids. Cake is roughly half the volume of the original tailings. The second step involves subsequent dewatering of the cake—placed in 1- to 2-m-thick annual lifts—by natural processes including consolidation, desiccation and freeze-thaw, delivering a trafficable surface that can be reclaimed.
Syncrude’s water-capping tailings technology involves the placement of water over a deposit of fine tailings to form a lake. Syncrude said it has demonstrated this technology on a pilot scale over more than 20 years of research, including numerous test ponds of various sizes, and is currently estab-lishing a commercial-scale project to serve as a demonstration of the concept. Although the method doesn’t meet the Directive 74 goal of providing a traffica-ble surface, Syncrude notes that it offers an approach that can result in a sus-tainable ecosystem that would be capa-ble of supporting aquatic life forms.
After receiving approval from regula-tory agencies to move ahead on the commercial-scale water-capping pro-ject, located at its Base Mine Lake tailings pond, Syncrude has begun preparatory steps to demonstrate the concept by stopping tailings flow into the lake, removing the tailings piping system, and starting fresh-water inflow from a nearby reservoir into the 8-km 2 pit lake. The intention is to allow heav-ier tailings to sink to the bottom of the pit lake while naturally occurring bacte-ria consume napthenic acids and hydro-carbons commonly found in oil sands tailings, eventually resulting in a non-toxic environment that is not harmful to birds and can support aquatic life. According to Syncrude, a 5-m-deep layer of fresh water atop the existing tailings fluids is necessary to shield the in-place tailings from disturbances that would inhibit settling.
If the concept is proven successful, Syncrude has plans to convert about half of the 30 or so pit lakes that will exist at the end of mining into water-capped tailings storage facilities. The company will closely monitor Base Mine Lake over the next decade to assess the progress of the project. Apart from the benefit of achieving an accepted form of reclama-tion if the method turns out to be effec-tive, Syncrude hopes to reap monetary savings from what would be a very low-energy form of tailings management.
Weir’s Mega-barges in Service at Suncor Tailings Project
Weir Minerals Canada (WMC) won an order in early 2010 to supply three Multiflo mega-barges, pictured below, for Suncor’s TRO tailings management project (see accompany-ing article). This past spring, WMC and its team of contrac-tors completed project construction prior to the hand-over to Suncor for commissioning. The system, says WMC, is now fully operational.
The project is the largest of its kind for WMC, and startup
marked culmination of months of effort on the part of sever-al key groups within Weir Minerals. The effort began in the
The complete turnkey project, which includes design, fab-rication, on-site construction, launch and supply of all equip-ment—including the Hazleton pumps shown here (right), the barges and their mechanical, electrical, process control and marine design components—represents a multi-million dollar endeavor for Weir Minerals.