Water availability is beginning to impact oil sands development and as a result, several technologies to increase the percentage of recycle water are being evaluated. One such option which is being re-evaluated is the use of centrifuges to produce a dry tailings which can accommodate overburden and soil replacement. Previous evaluations of centrifuge performance to capture water from the clay and silt tailings (mature fine tailings) components demonstrated some success, but at the time unacceptable costs. A better appreciation of the long term costs of mature fine tailings storage has prompted a reevaluation of centrifuge technology. The use of additives to improve centrifuge performance has significantly improved the results which can be achieved. Aside from the obvious positive environmental benefit of reclaiming the fluid fine (mature fine) tailings, the increase in the amount of water recycled will decrease the requirement to use the limited water in the Athabasca river. This paper discusses a laboratory scale study of the water chemistry and clay/silt feed properties which affect centrifuge performance, along with 20 tonne per hour pilot scale results.
The term dry stackable tailings is commonly used in oil sands tailings management to mean a mineral stream left over from the bitumen extraction process which can be stored without the need for dikes or other fluid containment structures. The water required for the bitumen extraction process results in mineral tailings streams in the form of slurries or suspensions, that require containment. In general, surface mined oil sands tailings fall into three categories: sand tailings, fine tailings, and froth treatment tailings. Although the froth treatment tailings have important environmental implications due to their contamination with solvents or diluents from the froth treatment process, they are generally combined with the other tailings prior to discharge into the recycle water area (tailings settling pond). Typically it is a straightforward process to create dry stackable tailings from the sand tailings, and they are often used to build the containment for the remaining fluid fine tailings.
It is another common practice for the surface mined oil sands industry to define sand as mineral particles greater than 44 microns. Fines are therefore less than 44 micron, and this definition can be useful when discussing the long very clearly, however, that it is the clay content that determines all of the important properties of the fine tailings or fluid fine tailings. (or mature fine tailings, when the solids content exceeds about 25%)(1–3). Over the entire mine, of course, the average clay to fines content is fixed, and the fines content can be a useful approximation tool for large scale planning purposes and the prediction of sand volumes and the fine tailings volume that will require containment.
The clay content, often expressed as a clay to fines ratio, can vary across an oil sands lease by as much as a factor of