Process for secondary recovery of bitumen in hot water extraction of tar sand

It has been found that tank-type air flotation cells are more efficient, when treating hot water process middlings containing in excess of about 3% bitumen, than trough-type air flotation cells. Also, it has been found that the trough-type cells are more efficient than the tank-type cells when treating middlings containing less than about 3% bitumen. Thus a secondary recovery circuit is proposed wherein the middlings are first treated in one or more tank-type cells in series and the underflow from the last tank-type cell is treated in one or more banks of trough-type cells.