Abstract: In order to wash inert materials, even of a large size, with a limited amount of washing liquid and with a lesser consumption of energy and without moving metal parts, apparatus having a plurality of tubular rotors (1) which are in side-by-side relation but spaced a distance from each other and are rigidly locked with a common shaft (13) which is horizontal or at an angle with respect to the horizontal, in which each rotor (1) has a plurality of transverse annular baffle plates (2) adapted to delimit corresponding annular channels (3) and having in each channel (3) a plurality of peripheral boxes (15). As the rotors (1) revolve, the washing liquid overflows to the outside over the lower baffle plate (2) of each rotor (1) and the material being washed, which is introduced through the mouth of the rotor (1) located at one end of the apparatus, advances against the current through all the rotors (1) until it is discharged from the mouth of the rotor (1) located at the other end.