We present a model for the motion of particles in an eddy current separation process. The model describes the action of the transient magnetic field of the separator by a first-order linear differential equation for the particle magnetic moment. From the model, qualitative conclusions can be drawn regarding the effects of particle size, shape and conductivity on the particle trajectory. It is also possible to solve the equations of motion for particles of simple shapes by numerical integration. The results of such simulations are compared with experimental data. The aim of the model is to improve the understanding of the behaviour of small particles in eddy current processes in order to optimize separator design and operation.