For a batch sedimentation test of a suspension formed by k particle categories, the settling velocity of a particle belonging to a category i, i=1,2,...,k, at a given time t and a given height x, from the bottom of the column, is a function of the terminal settling velocity of each category and of the concentration distribution by categories at (x,t). The mathematical model for this system is represented by k hyperbolic partial differential equations with the given initial conditions and the appropriate boundary conditions. The model allows a realistic description of the process and numerical simulations, using the donor-cell finite differences method, which are in good agreement with some previously published experimental data about bidisperse suspensions, when LOCKETT and AL-HABBOOBY or SELIM et al. relative fluid-particle velocity expressions were used.