A kinetic mathematical model was developed to describe the operation of the multi-spigot hydrosizer. The model is based on the description of two fundamental mechanisms: particle segregation and particle dispersion. Starting from the integral form of the continuity equation, applied to a discretized space, a system of ordinary differential equations, which includes the two mechanisms, was derived. The resulting system of differential equations describes the work of the teeter bed that exists inside each classifying chamber of the hydrosizer. A computational algorithm was developed to solve the model equations, based on a second-order precision predictor-corrector method. Timed samples were collected on the new six-spigot MEP Hydrosizer at present time working in Barroca Grande plant at Panasqueira mine (Portugal). The experimental data consist of the size distributions, the grades in tungsten trioxide and arsenic for each size class, the volume flow rates, and the pulp densities for each product yielded by the hydrosizer. The model was fitted to the experimental data, employing an optimization algorithm for non-linear unconstrained least-squares problems. It was found good agreement between the simulated and experimental results. (C) 2009 Elsevier Ltd. All rights reserved.