One of the biggest challenges for oil sands mining companies is reclaiming fluid fine tailings. In oil sands open-pit mining processes, warm water is used to separate the heavy oil (bitumen) from the sands. The by-product of this process is a mixture of water, clay, sand and residual bitumen. This material is sent to a tailings pond, where the sand and clays begin to settle out, allowing the process water to be recycled and used again in the mining operation.
While the sand settles quickly to the bottom, the fine solids such as the clays and silts create a floating layer below the surface of the water called fluid fine tailings (FFT). One of the technologies that speeds the release of process water from the FFT for recycling and minimizes tailings pond size is centrifuge technology. The centrifuge technology process consists of three steps. The FFT is dredged from the tailings pond. A polymer (the same kind that is used at a municipal water treatment plant) is added to the FFT slurry. The slurry is then fed into a centrifuge that spins the water out and produces a clay material that has the consistency of a mud cake.
The process water is returned to the tailings pond while the clay material is transported via truck and placed in an area that will allow for further consolidation. Once the clay material is sufficiently dense, it is capped with sand and reclamation soils, and then planted with trees, shrubs and other native vegetation.
Centrifugation technology is now considered commercially ready, with Syncrude Canada building a full-scale centrifuge plant estimated to cost $1.9 billion and operational since 2015. The full-scale plant has 18 centrifuges and is winterized to be operational year-round.
Syncrude has developed this technology methodically over the past decade, beginning with a proof of concept at a lab scale in 2005; proof of concept at a pilot Scale in 2007; work in 2008 focused on centrifuge operation; work in 2009 focused on the geotechnical characteristics of the centrifuged tailings deposits; work in 2010 focused on scale-up, flocculent mixing, by-product transport and deposits; work in 2011 involved a commercial prototype to understand throughput and commercial readiness; work in 2012 and through to 2014 before operating a commercial FFT centrifugation demonstration plant.
The environmental benefit of centrifugation is immediate as it speeds the release of water from FFT and leaves behind a clay material that is dense enough and strong enough to meet the Alberta government regulations for tailings materials that can be used as a base for landform design and reclamation. This means the clay material can be transported via truck and placed in an area slated for reclamation. Once the clay material has consolidated and settled, it is capped with sand and reclamation soils, and then planted with trees, shrubs and other native plants.
Over the long-term, speeding release of process water means more is available for recycle, and being able to reclaim over condensed fine tailings clay material reduces the size of tailing ponds needed for future continued operations.
Syncrude contributed the centrifuge technology to the COSIA Environmental Priority Area (EPA), which means it is available to all Tailings EPA members. Shell Canada was the first to pick up the technology, commissioning a commercial-scale demo plant (with two centrifuges) at Jackpine Mine. Operational since 2014, and is used to assess the applicability of the technology for a full commercial installation. Learnings by Syncrude or any other COSIA member are freely shared with the larger EPA group.