Treatment of primary tailings and middlings from the hot water extraction process for recovering bitumen from tar sand

The primary tailings and middlings are combined and fed to a vessel having the general form of a deep cone thickener. The feed is deflected outwardly and generally horizontally by a baffle, as it is delivered to the vessel. Simultaneously, the outwardly radiating layer of newly added feed is contacted from below by an upwelling stream of aerated middlings, which stream moves in parallel with the aforesaid layer. Bitumen froth is formed and recovered. The upwelling stream is provided by circulating middlings through eductor/aerator assemblies and a plenum chamber mounted centrally in the body of middlings in the vessel. A generally circular circulation of middlings is generated. In this manner, the newly added bitumen is quickly and efficiently recovered. Recirculation of middlings to the aeration zone yields an additional recovery of bitumen. Use of the deep cone ensures that the tailings from the vessel are relatively low in water and bitumen content.