The minimum fluidization velocity for coarse ores, of which fluidization behavior is governed by the force of inertia, increases with temperature while that of fine ores smaller than about 1500 ㎛ decreases. As the gas velocity increases, the abrasion and degradation in coarse ores are more severe but the elutriation rate and the concentration of fine ores entrained in gas also increase and it finally results in a high elutriation loss.