Fluidized bed medium separation (FBMS) was applied to separate objects with a small specific gravity difference by precisely controlling the apparent specific gravity of gas-solid fluidized bed with binary particle systems. The binary systems of particles with various specific gravities and diameters were employed, and the apparent specific gravity of fluidized bed, gfb and the dispersion, Δgfb, were measured by changing the bulk volume fraction of heavier particle, Vhp, and the superficial air velocity, u0. It was found that gfb can be controlled by Vhp and u0 because gfb varies with the total mass of particles and the bed expansion. On the other hand, since Δgfb is determined by the extent of segregation of fluidized particles and the fluidization intensity, Δgfb decreases with reducing the extent of the segregation and the vertical fluctuation of fluidized bed surface. The experimental results showed that practical fluidized conditions for FBMS are in the range of gfb≈0.5-3.8 and Δgfb≤0.1. Under these fluidized conditions, plastics with a small difference in specific gravity (0.04-0.24) were almost completely separated at the top and the bottom of the fluidized bed.
