Abstract: Industrial apparatus for mixing viscous material comprising a stationary mixing tank (1) having an inlet (7) and an outlet (8), a rotary stirring element (12) within the tank, duct means (23) interconnecting said outlet (8) and inlet (7), and an impeller (18) mounted for rotation with said stirring element (12), to thereby urge said viscous material towards said outlet (8) to at least assist the flow of material from said outlet through said duct means (23) to said inlet (7) and its recirculation through said tank (1). A macerating pump (29) is interposed along said duct means (23) to assist with mixing and recirculation.