In one aspect, the present invention relates to a method of conditioning raw tar sand to render it suitable for the separation of bitumen from the tar sand by froth flotation. In another aspect, the present invention relates to a method for processing raw tar sand to produce a bitumen enriched tar sand product more suitable for subsequent extraction of bitumen. In yet another aspect, the present invention relates to upgrading the bitumen content of tar sands through separation by froth flotation of a milled tar sand slurry to produce a concentrated tar sand product. In still a further aspect, the invention relates to a method whereby components of the tar sand slurry may be recovered and recycled for reuse. In yet another aspect, the present invention relates to the preparation of a fluid medium suitable for use in the separation of bitumen from tar sands by froth flotation.
Tar sands (also known as oil sands and bituminous sands) are sands which are impregnated with dense, viscous petroleum. Technically, the material should perhaps be called bituminous sand rather than tar sand since the hydrocarbon is a bitumen (i.e., a carbon disulfide-soluble oil). Herein these sands will be referred to as "tar sands". Deposits of tar sands are found in many countries, for example, Canada, the United States, and Venezuela. Tar sand deposits found in the Province of Alberta, Canada are being exploited commercially. In the United States, tar sand deposits are found in the Uinta basin of Utah and Colorado. These tar sands deposits contain billions of tons of tar sands which would be very valuable provided an economical method of separating the bitumen from the sand was available.
At present, the Canadian tar sands have been the subject of most of the research and development efforts conducted to date. The Canadian tar sands deposits are characterized by a sandstone grain covered by a layer of water which is covered with bitumen. Two methods of recovery of bitumen from these Canadian deposits are known as "the cold water method" and "the hot water method".
The "cold water method" does not involve heating of the tar sand other than whatever heating may occur during normal factory operations. The process involves mixing the tar sand with water at ambient temperature, soda ash and an organic solvent. The mixture is then permitted to settle at ambient temperature and a mixture of solvent and bitumen dissolved in the organic solvent rises to the top of the settling zone, much in the manner of cream rising in milk, and is recovered. The cold water method has not achieved commercial acceptance in Canada due to the physical nature of the Canadian tar sands.
The best known and most widely used method in the recovery of bitumen from Canadian tar sands is often referred to as the "hot water method". In general, the hot water process involves heating the tar sand with steam or hot water, milling the tar sand with a small portion of water at about 175.degree. F., transferring the tar sand into a turbulent stream of circulating water and carrying it through a separation cell maintained at an elevated temperature of about 180.degree. F. In the separation cell, entrained air causes the oil to rise to the top and form a froth rich in bitumen which is then drawn off. The sand settles to the bottom and may be removed. It is believed that separation of bitumen from Canadian tar sands is effected by disruption of the sheath of water surrounding the sandstone grain thereby also disrupting the bitumen covering of the water sheath, allowing the bitumen to rise to the top of the separation cell. The basic hot water system may be enhanced as described in U.S. Pat. No. 3,573,196 issued to Cymbalisty on Mar. 30, 1971, by adding a light hydrocarbon solvent to the slurry which is at a temperature below the boiling point of the solvent and subsequently heating the slurry to the boiling point of the hydrocarbon solvent, which volatilizes the solvent and assists in the separation of the bitumen.
These methods have been used to process the raw tar sand as mined. Raw tar sand ores typically contain from about 6% to about 12% bitumen by weight. Thus, treatment of the raw ore by both methods requires enormous quantities of water in relation to the bitumen recovered because of the low bitumen content in the raw tar sands. The cold water method described above as well as using large quantities of water requires large settling ponds. The hot water recovery method permits an energy recovery in the range of 50 to 60% of the bitumen processed. In other words, approximately one-half of the energy value of the recovered bitumen by the hot water method is consumed in its production.
The present invention provides a method whereby the raw tar sand ore may be concentrated, thereby increasing the bitumen content of the tar sand processed for bitumen recovery. By utilizing cold (ambient) water in the concentration of the tar sands in accordance with the method of the present invention, the amount of energy necessary to extract the bitumen from the concentrated tar sand is less per unit of bitumen recovery. Another advantage of the present invention is that the froth flotation apparatus utilized is less expensive to purchase, operate and maintain, and consumes less energy than the specially designed attritioning devices utilized in the hot water method. Potentially, an energy recovery rate of 90% is possible. In still another aspect, the invention allows the utilization of standard equipment readily available in the market. The method allows for recycle of the water agents thereby reducing water consumption, which is an important factor in recovery of bitumen from tar sands in the Western United States.