Slurry Tank Conditioning of Oil Sands: Tailings Behaviour

Slurry tank conditioning as an oil sands process step prior to extraction can be expected to produce a tailings material significantly different from conventional Clark hot water process tailings. Recycle water pond design and operation will depend upon the settling and consolidation properties of the fine tailings stream, and these properties in turn depend upon the chemical and physical conditions to which the oil sands are exposed in the extraction process. Slurry tank conditioning occurs at 50°C and without the addition of any process aides. The release of bitumen from the sand matrix is accomplished using mechanical agitation (stirring) in a tank, prior to desanding and flotation using conventional oil sands separation processes. This is in contrast to the Clark process which conditions the oil sand using tumblers, heat (80°C), and an alkaline water chemistry. The alkaline water chemistry serves to disperse the fine clays, as well as enhance the release of natural surfactants in the bitumen. Both of these effects result in rapid release of bitumen from the sand, allowing for very short residence times (5 to 10 min) in the tumblers. The non-alkanine water chemistry, and (longer residence time) mechanical conditioning in the slurry tank process results in a reduction in dispersion of the fine clays, as well as an increase in the flocculation and settling rate, compared to the Clark process tailings. The rapid flocculation and settling of the fine clays results in a fine tailings stream that begins settling without any induction time and that has a solids free release water. The slurry tank process tailings have an order of magnitude higher permeability than Clark hot water process tailings and they have a significantly improved capacity to support a sand surcharge which will provide a stress to further enhance dewatering, relative to the Clark tailings. The improved capacity to support a sand surcharge indicates that a lower calcium addition would be needed to create CT (relative to Clark tailings). Because of the similar water chemistry, slurry tank and OSLO tailings behaviour will be similar, with the additional potential benefit of tailoring the degree of mechanical conditioning in the slurry tank to maximize bitumen recovery, but minimize clay dispersion. The beneficial fine tailings properties result from both the water chemistry, as well as the more controlled mechanica! conditioning in the slurry tank. Depending upon the connate water chemistry of the oil sands, maintaining a non-alkaline environment after many years of recycle may require chemical treatment of the recycled water. For the lease 13 oil sands tested here, chemical treatment is not likely to he required to control the water chemistry. Toxicity of the release water is significantly lower for the slurry tank conditioned oil sands than for the Clark tailings, although it has some level of toxicity. This means that in any treat and release scenario, the slurry tank conditioned tailings will require less treatment than conventional Clark tailings.