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 unconventional tar sands deposits are oil-wet has led to a focus on solvent-based bitumen extraction processes for these types of materials. Utah's Asphalt Ridge deposit is a case in point, except that, 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 ton 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 mining of oil sands in Alberta. Introduction CANMET's Energy Technology Centre in Devon became involved in the Asphalt Ridge tar sands project when it was a solvent-based extraction operation hampered by a significant emulsion build up 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 solvent and clay mineral interactions would be unacceptably high. As a result, a series of standard tests were applied to Asphalt Ridge tar sand samples in order to assess the potential of a water-based extraction process(1,2). 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 30 years in Alberta(3–8). 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 from about 80 °C to less than 50 °C by increasing the mechanical energy input(9–12). 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 processing the Asphalt Ridge tar sand without solvents may have been due to improper handling of cores or bulk samples resulting in oxidation or weathering(18–21). In spite of the nominally oil-wet nature of the Asphalt Ridge tar sand, the bitumen can be extracted using a water-based process. Water-based bitumen extraction involves two key steps, referred to as conditioning (where the bitumen is separated from the mineral) and flotation (where the bitumen is concentrated in a series of flotation cells).

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