Force index computation for a magnetic separator based on permanent magnet Fatima Ezzahra Kassid, Essaâdia Azelmad, Lahbib Bousshine and Abdelmajid Berdai E3S Web Conf., 280 (2021) 07013 Published online: 30 June 2021 DOI: 10.1051/e3sconf/202128007013