Enhancement of copper dissolution by mechanochemical activation of copper ores: Correlation between leaching experiments and DEM simulations

In this work we investigated the influence of planetary ball milling and vertical stirred ball milling on the leaching of a copper ore containing copper sulfate and covellite. We used a mixed experimental-simulation approach to correlate the kinetic parameters of leaching to the collision energy during grinding. The effect of milling was studied by scanning electron microscopy (FE-SEM), X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS). Results showed that both high-intensity grinding techniques resulted into a dramatic decrease of particle size. Furthermore, under specific grinding conditions, the planetary ball milling determined also the partial amorphization of covellite. The collision energies corresponding to specific grinding conditions in terms of rotational speed and number of grinding media were assessed by DEM simulations and were related to the specific surface area after grinding. The specific surface area of grinded samples was found to be directly proportional to the collision energy in grinding. The leaching of the ore occurred through three subsequent steps: (i) dissolution of copper sulfate, (ii) dissolution of amorphousized covellite and (iii) dissolution of residual crystalline covellite. The results of kinetic fitting highlighted an increase of the rate constants for the leaching of amorphous and crystalline covellite by intensifying the milling conditions. By correlating the collision energies from DEM simulation with the leaching rate constants, we confirmed that the rate constants for the leaching of covellite increased due to an occurred mechanochemical reaction. The mechanochemical reaction that determined the partial amorphization of covellite occurred above 0.25 J/s · g. On the other hand, the rate constants for the leaching of the residual crystalline covellite constantly and progressively increased with the collision energy, thus highlighting an improvement of leaching due to an increase of surface area.