| Description |
The world's tar sand deposits appear to be divided into two basic types, characterized by the way in which the tar and sand are associated within the ore structure. In the first, the tar or bitumen in the ore is separated from the silica sand grains by a film of water. These sands are designated water-wet and are typified by the large deposits in the Athabasca region of Canada. The other type is oil-wet sand, in which the bitumen is bonded directly to the sand grains with little or no water present. Much of the tar sand found in the United States, particularly in Utah, where 90 percent of the country's known reserves are located, is oil-wet. Most of the oil-wet sands contain less than 5 percent fine material, which appears to be mostly fine particles of alpha quartz, similar in composition to the larger sand particles and not the clay minerals typically associated with the Canadian water-wet ores. The bitumen associated with the Utah oil-wet tar sands is also much more viscous, in some cases by several orders of magnitude, than the bitumen found in Canadian tar sands. Some Utah bitumen also can contain an order of magnitude less sulfur than the Canadian bitumen. A processing strategy for separation of bitumen from water-wet tar sand was successfully worked out by the early Canadian researchers, and the so-called "Clark" hot water process has been successfully applied to two large commercial plants now operating in Canada. However, heretofore, the Clark process and its variations have not been successful in processing oil-wet tar sands ores. A research team at the University of Utah, headed by two of the authors (Oblad and Miller) has developed a package of processing strategies for the separation of bitumen from these oil-wet sands. The principal work has been previously reported in the literature (Misra& Miller, 1980, Sepulveda, Miller, & Oblad, 1976; Sepulveda & Miller, 1978; Sepulveda, 1977). |
