Flotation method and apparatus for recovering crude oil from tar-sand

This invention relates to an improved method and apparatus for scrubbing crude oil (bitumen) from tar-sands, the apparatus being characterized by a heated vessel for maintaining the tar-sand/water slurry at between approximately 180.degree.-200.degree. F., a pair of counterrotating screw conveyors in the bottom of the vessel for agitating the sand and moving it to the discharge end, means for simultaneously diluting and aerating the incoming slurry that produces small bubbles effective to float the crude oil freed from the sand to the surface, an overflow wier running alongside the vessel for catching the oil skimmed off the surface of the water, transversely-extending endless chain-and-flight skimmers for skimming the oil into the wier, a bottom-opening discharge for the clean sand, and valves controlling the discharge of sand effective to remove the latter without lowering the fluid level in the vessel to a point where the oil previously released can reattach itself to the sand. The method encompasses the steps of submerging the tar-sand in a hot water bath agitating the sand while thus immersed while continuously bubbling air up through the slurry to float the oil particles freed from the sand grains to the surface, continuously skimming off the oil floating on the water bath from the surface thereof, and withdrawing the clean sand from the bottom of the vessel intermittently and quickly enough to prevent the level of the water bath from falling below the top of the screws.