This work concerns the use of a pneumatic classifier in the valorization of fly ash. This classifier is characterized by a rotor positioned vertically. Firstly, a study in laboratory was carried out. Three parameters were retained: the rotation speed of the rotor, the air flow and the ash feeding rate. The main parameter is the rotation speed of the rotor. There is a relation between the cut diameter and the speed rotation: d(50) = K/V with V as the speed and K as a factor in function of the process. The increase of the air flow and the ash feeding rate favours the extraction of the fine particles. After that, we realized a study of the industrial feasibility of the selection. We observe the same relation as those obtained during the laboratory study. We have found a set of operating parameters so as to obtain four granulometric fractions (<10, <30, <50 and <80 mu m).