The mixer has a loading arm (15) for carrying a loading cutter (25), and a displacement device (28) comprising a front roller that is placed near and downstream of the loading cutter. A posterior roller (30) of the displacement device is placed near a mixing tank. A conveyor belt (31) is wound around the front and posterior rollers, and the arm carries a tensioning device (34) of the belt. The tensioning device comprises a jack (36) that is connected to the front roller and the arm such that actuation of the jack causes displacement of the front roller relative to the arm.
