Dr. J. Don Scott is Professor Emeritus, Geotechnical Engineering at the University of Alberta.
Dr. Scott reviews the properties that negatively effect the consolidation of oil sand's fine tailings. These properties include: oil sands ore, tailings stream, thixotropy and overconsolidation, and biogenic gas. The AER 2013 report on how the four oil sands companies were doing in capturing the fine tailings did not report the success you would anticipate after 30 years of researching the problem. Intermittent clay shales layers in the bitumen are the source of the fine tailings. Biogenic gas from the tailings ponds, mainly methane and a bit of CO2, creates channels up through the MFT. MFT solids content increases but density does not. So he calls attention to the action of biogenic gases in understanding MFT consolidation. .
Dr. Scott also discusses the results of thixotropic strength tests, as well as a thirty year study in the interface settlement of mature fine tailings in standpipes. He describes the process as "creep" not consolidation and the implications for lab measurements.
In conclusion, Dr. Scott discusses the properties of fine fluid tailings, and that dispersed fines are the "major hostile property" in the tailings. He also raises the issue that clay-shale aggregates and clay booklets are dispersed considerably more in research projects than what actually happens in the mining, extraction and tailings disposal processes.
Dr. Scott points out that the biogenic gas processes needs to be studied more and densities of MFT are not commonly measured. He discusses over-consolidation stress and thixotropic strength measurements in the lab compared to the field and points out the limitations.
Dr. Scott's presentation was a part of the Tailings and Mine Waster conference in Banff, Alberta, in November 2013.
