We report the investigation of a chalcopyrite leaching process that implements millimeter-sized glass beads that are stirred in the leach reactor to combine particle grinding, mechanical activation, and surface removal of reaction products. The paper focuses on demonstrating the impact of the so-called attrition-leaching phenomenon on the leaching rate of a chalcopyrite concentrate and provides a first understanding of the underlying mechanisms. For this purpose, we have compared the copper leaching yield for different configurations under controlled chemical conditions (1 kg of glass beads and 84 g of chalcopyrite concentrate in 2.5 L of H2SO4-H2O solution, pH = 1.3, Eh = 700 mV vs SHE, and T = 42 °C). On top of elemental analysis of the leach solution with time, we provide a full characterization of the solid residue based on X-ray diffraction, elemental analysis, and sulfur speciation. We demonstrate that glass beads led to a remarkable enhancement of the leaching rate in conditions where particles were already passivated by simple leaching and even when large amounts of solid products (elemental sulfur and jarosite) were present. An in-depth evaluation of particle size distribution showed that particle breakage occurred during a rather short time (a few hours) at the beginning of the runs, transforming the initial particles with d4/3 = 30 μm to finer particles with d4/3 = 15 μm. Then, particle breakage almost stopped, while an attrition phenomenon was evidenced, inducing the formation of very fine particles (<1 μm) and aggregates concomitantly with copper leaching.