Aerating tar sands-water mixture prior to settling in a gravity settling zone

Claim 1

An improved process for the recovery of bitumen from tar sands comprising: a. forming a mixture of tar sands and water at a temperature in the range of 130° to 210°F. including that of the hereinafter specified recycle stream of aerated bitumen-rich middlings material; said mixture containing 0.2 to 3.0 pounds of water per pound of tar sands; b. settling the mixture in a separation zone to form an upper bitumen froth layer, a middlings layer containing water, silt, clay, and bitumen, and a sand tailings layer; c. separately removing the bitumen froth layer and the sand tailings layer; d. passing a stream of middlings layer into an air scavenger zone and therein aerating said stream to provide additional bitumen froth; e. recovering the froth from the scavenger zone; f. passing a second bitumen-rich middlings stream to an aeration zone and mixing air into the middlings stream in said aeration zone and g. admixing the aerated bitumen-rich middlings from said aeration zone with the mixture of step (a).