Separating chalcopyrite, an important copper-containing ore, from pyrite is an important mineral-processing objective. Herein, we report the synthesis of S-hydroxyethyl-O-isobutyl xanthate (HEIBX), a novel surfactant bearing both hydroxyl and thione groups, through the attachment of a hydroxyethyl group to sodium isobutyl xanthate (SIBX), and its first application as a flotation collector for the selective flotation-separation of chalcopyrite from pyrite. The flotation mechanism involving HEIBX and chalcopyrite or pyrite was investigated by DFT calculations, UV-vis spectroscopy, contact-angle and surface-tension measurements, flotation and zeta-potential experiments, as well as FTIR spectroscopy and XPS. Incorporation of the hydroxyethyl group was observed to increase the molecular properties of SIBX by increasing the number of active sites, arrangement density, selectivity and hydrophobicity, thereby improving its flotation performance. Chalcopyrite was separated from pyrite using 4 x 10(-5) mol.L-1 HEIBX at pH similar to 8.0. Furthermore, we found that the hydroxyl and thione functional groups adsorb onto the chalcopyrite surface though the formation of C-O-Cu and C-S-Cu bonds. (C) 2019 Published by Elsevier Ltd.