Selective Depression of Sphalerite by α-Cyclodextrin in Chalcopyrite–Sphalerite Flotation Separation

α-Cyclodextrin (α-CD) was evaluated as a selective depressant for chalcopyrite–sphalerite flotation. Single-mineral and artificial mixed-mineral flotation tests were combined with contact angle, zeta potential, Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) analyses. α-CD depressed sphalerite while exerting little effect on chalcopyrite. Without α-CD, the Cu and Zn grades of the concentrate were 17.84% and 30.12%, with corresponding recoveries of 92.37% and 79.65%, respectively. At pH 8, with 30 mg/L sodium butyl xanthate and 500 mg/L α-CD, flotation of a 1:1 artificial mineral mixture produced a concentrate with a Cu grade of 31.45% and recovery of 98.61%; the Zn grade and recovery were 3.52% and 5.64%, respectively. Compared with xanthate treatment alone, α-CD pretreatment lowered the contact angle of sphalerite by 36.1°, versus 3.2° for chalcopyrite. FTIR and XPS analyses indicated an increase in oxygen-containing species on the sphalerite surface, whereas the main Cu 2p and S 2p spectra of chalcopyrite remained largely unchanged after α-CD treatment. These results are consistent with preferential adsorption of α-CD on sphalerite and increased surface hydrophilicity, explaining its selective depression in this mineral system.