Abstract: In an apparatus including a column through which the liquid and the divided solids to be treated thereby circulate in counter-current, the treated solids which tend to collect at one of the column being conveyed hydraulically by a fraction of the liquid introduced into the column towards separating means from which the said fraction is re-cycled into the column, the circuit of the liquid intended to circulate through the column and the circuit of the liquid intended to convey the treated solids are wholly separated from each other, the first one comprising a first inlet nozzle directed towards the other end of the column and the second one a second inlet nozzle directed towards the inlet of the conduit through which the treated solids are hydraulically conveyed, this second nozzle being located between the first one and the adjacent end of the column. In the case of solids heavier than the treating liquid, both inlet nozzles are disposed axially in a chamber provided at the lower end of the column.