Engineering & Mining Journal

DEC 2012

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TA I L I N G S its Fluid Fine Tailings—Centrifuging Full Scale Plant (FFT-CFSP) in Fort McMurray, Alberta. KBR Canada subsidiary, KBR Industrial Canada, will provide module fabrication and construction services for FFTCFSP. Module fabrication is scheduled to begin late this year and run through the end of 2013. Construction will follow with mechanical completion scheduled to allow plant start-up in 2015. Syncrude's centrifugation method is a two-step process. The first step involves MFT dewatering using horizontal solid-bowl scroll centrifuge technology 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- www.e-mj.com 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 establishing 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 trafficable surface, Syncrude notes that it offers an approach that can result in a sustainable ecosystem that would be capable of supporting aquatic life forms. After receiving approval from regulatory agencies to move ahead on the commercial-scale water-capping project, 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-km2 pit lake. The intention is to allow heavier tailings to sink to the bottom of the pit lake while naturally occurring bacteria consume napthenic acids and hydrocarbons commonly found in oil sands tailings, eventually resulting in a nontoxic 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 reclamation if the method turns out to be effective, Syncrude hopes to reap monetary savings from what would be a very lowenergy form of tailings management. DECEMBER 2012 • E&MJ; 63

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