Balling of finely comminuted solids by random coalescence and granulation of iron ore fines and other minerals by autolayering are two major size enlargement processes. The existing kinetic model for random coalescence does not take into account the strong dependence of coordination number on the size distribution of agglomerating entities. We present a coordination number based coalescence model, which mimics the underlying physical process more realistically. Simulations show that in spite of highly diverse model structures, random and coordination coalescence models give remarkably similar results. Only static models of autolayering are available presently. These map the input size distribution of feed solids into steady state or terminal size distribution of granules, with little or no information on the path traversed by the process. We propose a continuous-time dynamic model of autolayering within the population balance framework. The model, which is based on the proportionate growth postulate of autolayering, agrees reasonably well with experimental data. (C) 2003 Elsevier B.V. All rights reserved.