Residual solvent release from froth treatment tailings

Yuming Xu1, Jianying Wu1*, Tadek Dabros1, Jianmin Kan2

1: CanmetENERGY, Natural Resources Canada, 1 Oil Patch Dr., Devon, Alberta T9G
1A8
2: Total E & P Canada, Suite 2900, 240 â?? 4th Avenue SW, Calgary, AB T2P 4H4
*: Current address, Canadian natural resources limited, 2500, 855 - 2 Street SW Calgary, Alberta, Canada T2P 4J8
Froth treatment tailings (TSRU) contain trace amounts of solvent. When they are deposited into tailings ponds under water or on a beach, solvent evaporates and is released to atmosphere. Local accumulations of solvent and high evaporation rates would raise safety and environmental concerns. It is therefore important to understand the behaviour of the solvent release from the TSRU tailings. Solvent release was studied using two approaches: 1) kinetic modeling, and 2) experiments simulating solvent release under two different scenarios: subaqueous deposition and subaerial deposition. A diffusion-controlled kinetic model was used to predict the solvent release from subaqueous deposition at temperatures below the solvent boiling point. A kinetic model based on continuity equations was found to successfully model solvent release from unsaturated tailings under aerial conditions at ambient temperature. However, at temperatures above the solvent boiling point, solvent release generates bubbles and produces foam. The foam formation changes the characteristic of tailings and makes the modeling very difficult. Experimental results demonstrated that solvent is released from subaqueous tailings very slowly due to the lack of agitation and mixing. Solvent trapped in the sediment did not effectively keep the overlying water saturated with pentane. Solvent release from aerially deposited beaches is faster than from subaqueous deposits; for instance, at 22°C after 24 h, only 15% of the solvent remained in aerially deposited tailings, compared to 90% remaining in subaqueous tailings under the experimental conditions.