The effect of glass particle size on the crystallization kinetics of an iron-rich glass from a nickel leaching waste has been investigated by means of differential thermal analysis (DTA). The results show that the crystallization of a pyroxene phase occurs by bulk nucleation from a constant number of nuclei. The crystallization mode and the dimensionality of crystals are strongly dependent on the glass particle size, 100 mu m being the critical size. Glass fractions with particle size > 100 mu m show three-dimensional crystal growth controlled by diffusion, whereas a particle size < 100 mu m leads to an interface reaction mechanism with two-dimensional growth of crystals.