The degree of separation in the recovery of cenospheres from coal fly ash has been estimated for both wet and dry separation processes by applying the terminal velocity concept of particles. Particle diameter and density were determined by sieving industrial cenospheres and coal fly ash type IV, the model particles. This information was then utilized to calculate the terminal velocity needed to estimate the separation performances of both the wet and dry separation processes. Based on this estimation, the dry separation process performed similarly to the wet separation process, with an optimum Newton's efficiency of 0.54, only slightly lower than that of the wet separation process of 0.6. Moreover, it was observed that the cenospheres were concentrated in the underflow product, whereas for the wet separation process the reverse was true. The findings of this assessment were verified using a micron separator. Similar tendencies in the concentration of cenospheres in the underflow products were obtained. An optimum Newton's efficiency as high as 0.44 was achieved, with 66% recovery of the cenospheres. The recovery of the cenospheres was only 4% lower than the estimated value (70%), from which we conclude that dry separation processes are interesting technologies to apply to the recovery of cenospheres from coal fly ash because of their high efficiencies. (C) 2010 Elsevier B.V. All rights reserved.