Finite Element Modeling of Selective Liberation of Copper Slag Under Impact Crushing

Recycling large-tonnage copper slag as a secondary source of iron in the form of magnetite is limited by the liberation of finely disseminated phases, whereas particle shape has so far been regarded as a consequence of breakage rather than a controllable feed parameter. In the finite element model, particle contours were taken from optical micrographs, while the third dimension and the texture with explicitly resolved phases and interphase boundaries were built using rules adopted from a published mineralogical description. Of 93 impact simulations, 68 formed the main sample covering seven particle shapes, impact angles of 30–90° and velocities of 22.5–80 m/s, the rest being control, tuning or rejected runs. Three slag samples were crushed in a disintegrator at rotor speeds of 1000–3000 rpm. For the series of particles of equal length, liberation is governed by the ratio of the smallest particle dimension to the grain size; the transition is threshold-like, and, for the adopted strength of interphase boundaries, the critical thickness increases with impact energy from about two to four grain sizes. With no parameters fitted to the experimental data, the calculated critical thickness is close to the threshold size of about 315 µm and of the same order as the median product size, while the concentration of liberated fayalite in the fine class and the rotor speed giving the greatest effect agree qualitatively with the simulations. Classification of the feed by size and shape is proposed as a strategy for further testing.