The vertical as well as horizontal dispersion for the gas-solid fluidization has been analyzed in the present work. The fluidization and solids mixing characteristics of large irregular particles (Geldart-BD type) for both homogeneous and heterogeneous materials (size-variant and density-variant respectively) have been investigated in a 15 x 100 cm(2) cylindrical column. A theoretical model for concentration of jetsam particles has been developed as a function of height of any layer of particles (measured from the grid) by considering the counterflow of solids and circulation model together with the dispersion model for the vertical and the horizontal displacement of the particles in the fluidized bed. The mixing index at any position in the bed has thereby been expressed as a function of the concentration of the jetsam. The values of mixing index calculated from the above model as well as the experimentally measured ones for both the homogeneous and the heterogeneous systems have been compared with each other. Attempt has also been made to develop correlations for the mixing index using various system parameters based on the dimensional analysis approach for the unpromoted and the promoted beds. The mixing index values thus obtained through the dimensional analysis approach have been compared with those obtained from the developed theoretical model. The values of the mixing index calculated for promoted beds have also been compared with the corresponding values for the unpromoted beds. Segregation effect is found to be stronger for the heterogeneous systems than the homogeneous ones. The density difference is the major factor affecting the segregation.