A novel thionocarbamate collector, O-n-butyl-N-isobutyl thionocarbamate (NBIB), was synthesized. The flotation test showed that NBIB has good selectivity under low alkali conditions. NBIB has a strong ability to collect chalcopyrite in the pH range of 6 − 11 though it is slightly affected by pH. The ability to collect pyrite is weak and decreases with increasing pH. The adsorption mechanism of NBIB was studied by adsorption measurements, UV–Vis spectroscopy scanning, contact angle measurements, zeta potential measurements, XPS and density functional theory (DFT) calculations. The results showed that the adsorption capacity of NBIB on the chalcopyrite surface is much larger than that on pyrite, and it is not affected by pH, which is consistent with the flotation test results. UV–Vis spectrum scanning showed that the interaction between NBIB and Cu²⁺ is stronger than that between NBIB and Fe²⁺. At pH = 9, the hydrophobicity of NBIB on the chalcopyrite surface is greater than that of pyrite. Zeta potential and XPS analysis showed that NBIB may have chemical adsorption on the chalcopyrite surface, but the interaction on the pyrite surface is very weak. DFT calculations further confirm that the bond atom of NBIB is the S atom of the C = S double bond, which has the conditions for forming chemical bonds with chalcopyrite.