The trajectories of real, scrap particles processed with an eddy current separator are compared to computer simulations to investigate the effects of particle shape and particle-particle interaction, effects that are difficult to catch in a purely theoretical model. The results show that the primary particle parameters are size, conductivity and initial orientation, provided that the size of a particle is defined in relation to the eddy current process. Therefore, the detailed shape of scrap particles is less important. The effects of particle-particle interaction on the grade and recovery can be predicted by considering two different types of collisions between nonferrous and nonmetal particles. This results in a simple theory that can be incorporated into a simulation model. (C) 2004 Elsevier B.V. All rights reserved.