The optimum rotational speed (RS) of a novel centrifugation method for obtaining high-purity Si separated from Al-Si melts was evaluated numerically and experimentally. Numerical calculations showed that the separation efficiency (Si to Al ratio in the separated solid) increases and finally reaches a plateau at a high RS. The calculated relationship between RS and the separation efficiency was consistent with experimentally measured data except for the removal of primary Si crystallites, which happened at centrifugation at 800 revolutions per minute (RPM). Based on the acquired data, it was established that 700 RPM is the optimal RS for our centrifugation apparatus (developed in a previous study) to maximize the separation efficiency. (C) 2015 Elsevier B.V. All rights reserved.