Abstract: The present invention concerns equipment for the leaching of solid matter from a sludge with the aid of a gas containing oxygen, the said equipment comprising a tall reactor (1) equipped with a central pipe (2) and from the reactor bottom (3), an upward-directed double-action mixer (5). The mixer is situated in the vicinity of the lower edge of the central pipe: the upper blades (13) of the mixer produce a downward suction flow from the central pipe, and the lower blades (14) disperse the gas to be fed into the sludge in the form of small bubbles, thereby preventing the solid matter from settling to the bottom of the reactor.