The dry dense medium separation of iron ore based on floating and sinking of ore particles in a gas-solid fluidized bed was investigated using zircon sand as the fluidized medium. The float-sink of ore particles with mean size D-ave = 23.6 mm was investigated as the fluidizing air velocity and the float-sink time were varied. It was found that gangue with density less than 2850 kg/m(3) which float is able to be separated from valuable ore with density greater than 2850 km/m(3) which sink. The set point (density where half the particles float and half the particles sink) decreases with increasing the air velocity, and that the float-sink separation is completed within 2 min. The influence of different sized ore particles in the float-sink experiments was also investigated. As a result, the iron ore with D-ave >= 17.6 mm are successfully separated. As D-ave decreases below 17.6 mm, the ore particles with density near the set point tend to scatter in the fluidized bed without floating or sinking, resulting in separation efficiency which decreases with decreasing D-ave. This indicates that the size of the ore particles is one of the major factors, to achieve high separation efficiency. (c) 2010 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.