Liquid-solid fluidized bed separators are one of the important types of equipment for the beneficiation of low-grade iron ore fines. Particles separate based on the difference in their terminal velocities in these types of separators. Misplacement of particles is a common phenomenon in such type of separators. Qualitative and quantitative studies of the misplacement of particles are essential for the complete understanding of the particle separation. The performance of fluidized bed separators depends on the particle separation. The present study looks into the qualitative and quantitative evaluation of the misplacement of particles inside a fluidized bed separator. The misplacement of particles depends on the particle flow or hydrodynamics. The misplacement of particles, studied using iron ore, quartz and their binary mixtures. The present study uses a new index called "misplacement index" to understand the particle misplacement quantitatively. Effects of different parameters on the misplacement of particles, evaluated experimentally. It is found that mean particle size ratio (MPSR), particle size, static bed height, particle component concentration in the feed, overflow height and superficial velocity have a significant effect on the misplacement of the particles. (C) 2016 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.