Beyond energy input: From dry grinding limitations to rheology-mediated wet micronization of calcium carbonate in a planetary ball mill

The micronization of calcium carbonate by planetary ball milling was investigated through a combined study of dry and wet grinding regimes to identify the factors governing ultrafine grinding performance. Dry grinding exhibited intrinsic limitations associated with agglomeration and unstable breakage behavior, preventing efficient micronization despite variations in operating parameters and grinding aid dosage. In contrast, wet grinding substantially improved performance, reducing particle size to approximately D50 ≈ 2 µm and D90 ≈ 4–5 µm within the identified operating window. Response surface analysis showed that grinding performance within the initial experimental domain was mainly controlled by rotational speed and grinding time, while the predicted optimum lay beyond the design space. Additional experiments under higher-energy conditions revealed a transition from an energy-dominated regime toward a slurry-mediated regime, where slurry rheology became a determining factor in process efficiency. An operating window was identified at 350–400 rpm, ∼50 min grinding time and 0.55–0.60 mL/g water-to-solid ratio, providing the best compromise between particle size reduction and process stability. These results show that wet planetary grinding performance is governed by coupled mechanical–rheological interactions and provide a mechanistic framework for optimization of ultrafine grinding of industrial carbonates.