Process and apparatus for classifying granular material suspended in a liquid

A method and apparatus according to which slurries are treated so as to achieve therefrom a final fraction in which particles smaller than a given size are suspended in a given concentration. The slurry is treated in a first liquid cyclone having an upper overflow discharge and a lower discharge for substantially dewatered matter. The upper overflow discharge is delivered from the first liquid cyclone to a second liquid cyclone which has an upper overflow discharge providing the desired final fraction. At least part of the dewatered matter discharged from the first liquid cyclone is delivered to a gravity separator to which liquid is supplied at a rate which controls the concentration of the particles in the final fraction. This gravity separator has an overflow which is returned to the first liquid cyclone, and the gravity separator serves to separate from the slurry therein particles which are larger than a given size.