The many advantageous properties of gas-fluidized beds have enabled its widespread use across many industries. In most industrial applications of fluidization the suspension consists of non-spherical particles of different diameters and sometimes-different densities. The materials of interest in the present study, sponsored by Huntsman-Tioxide, are industrial raw materials used in the manufacture of titanium dioxide pigment, the two materials belong to the Geldart Group B of the classification of powders and have the following characteristics; d_p1 = 186x10^-6m, density₁ = 4200kg/m³, d_p2=156x10^-6m, density₂ = 3200kg/m³. Eulerian-Eulerian models have become useful in the study of the hydrodynamic behaviour of particulate flows; this development has been facilitated by quantum leaps in computing power. In the Eulerian-Eulerian approach, both the fluid and particle phases are assumed to be interpenetrating continua and are described in terms of conservation of mass and momentum. In the present study, the Eulerian-Eulerian two fluid continuum model built in CFX 4.4 has been used to model and simulate the fluid dynamics of the mono-dispersed system of the two mentioned individual materials and their bimodal behaviour within the bubbling regime of fluidization. Granular Kinetic theory, which is already available from CFX 4.4, has been used for 2D time-dependent simulations for the mono-dispersed system of the individual materials. Model predictions have been compared with experimental data obtained on pressure, voidage and bed height fluctuations. The aim of the project is then to further develop the modelling work towards the simulations of the bimodal system at different weight fractions. To rise to this challenge, a new Particle Bed model, which makes use of volume-averaged mass and momentum balances for the fluid and particle phases, is proposed for the modelling of the bimodal particle mixtures. The model is used to investigate the stability and fluidization quality of the feedstock mixture, with model predictions compared with experimental data.