Laboratory and Pilot Experience in the Development of a Conventional Water-Based Extraction Process for the Utah Asphalt Ridge Tar Sands

Abstract The belief that the Utah tar sands deposits are oil-wet has led to a focus on solvent-based bitumen extraction processes, or some form of solvent assisted water-based extraction process for these types of materials. However, under certain conditions, this ore is in fact amenable to a conventional water-based extraction process. The thermal, mechanical and chemical environments necessary to make the Asphalt Ridge ore behave like an Alberta Athabasca oil sand are outlined, along with the typical criteria which must be satisfied for a novel extraction process to be viable. Laboratory-scale demonstrations of the efficacy of a Clark-style hot water extraction process for the Asphalt Ridge tar sands were subsequently confirmed on a twenty tonne per hour pilot scale. In addition, the scarcity of water at the mining and extraction operation in Utah led to the development of an aggressive tailings treatment process, which also offers lessons for tailings handling in the surface-mined oil sands in Alberta. Introduction The CANMET Energy Technology Centre in Devon, Alberta, became involved in the Asphalt Ridge tar sands project when it was a solvent-based extraction operation hampered by a significant emulsion buildup in the recycle water. In working to develop a solution to the emulsion buildup, it became apparent that, using the solvent-based extraction process, solvent losses associated with clay mineral-solvent interactions would be unacceptably high. As a result, a series of standard tests(1, 2) were applied to Asphalt Ridge tar sand samples in order to assess the potential for a solvent-free, water-based extraction process(3, 4). Surprisingly, some of these nominally oil-wet tar sands performed very well, indicating that the Asphalt Ridge tar sand bitumen could be extracted using commercially proven technology developed over the last 40 years in Alberta(5–10). In order to achieve bitumen recoveries similar to those for Athabasca oil sands, significantly higher mechanical energy levels were required, along with high temperatures. Since the early 1990s, the operating temperature used in commercial processing of Athabasca oil sands has been reduced from about 80 °C to less than 50 °C while increasing the mechanical energy input(1, 2, 11, 12). By maintaining both mechanical and thermal energy inputs at high levels, the ‘difficult to process’ Asphalt Ridge tar sand showed bitumen recoveries of approximately 90%; similar to the Athabasca commercial operations. The Asphalt Ridge tar sand samples that did not perform well in bench-top laboratory assessments were found to be weathered or oxidized; conditions that also inhibit extractability in the Athabasca oil sands in Alberta(13–17). The difficulties encountered by earlier researchers in using Canadian technology, or a modified water-based extraction process for the Asphalt Ridge tar sand (without pre-treatment with an organic diluent before ore conditioning), may have been due to improper handling of cores or bulk samples resulting in bitumen oxidation or weathering(18–24). In referring to the differences between the Utah tar sands and those in the Athabasca deposit, "These differences preclude the direct application of the Canadian mining and recovery technology to Utah's tar sands and to other United States tar sands(18)."

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