Effective separation of chalcopyrite and molybdenite by flotation with 2-mercaptonicotinic acid as a depressant: Insights into interfacial adsorption mechanism

Selective separation of molybdenite and chalcopyrite by flotation remains challenging due to their similar flotation behaviors and the environmental risks associated with traditional inorganic depressants. In this study, an environmentally friendly reagent, 2-mercaptonicotinic acid (2-MNA), was investigated as an effective depressant for the selective separation of molybdenite from chalcopyrite. Micro-flotation experiments demonstrated that, under non-acidic conditions, 2-MNA markedly depressed chalcopyrite but showed negligible effect on molybdenite, resulting in efficient mineral separation. For artificially mixed minerals, at pH 8 and a 2-MNA dosage of 25 mg/L, molybdenite recovery reached 93.75 % while chalcopyrite recovery decreased to 5.28 %. Characterization of interfacial chemistry through zeta potential and surface wettability analyses demonstrated that 2-MNA showed a strong affinity for chalcopyrite, significantly decreasing chalcopyrite’s hydrophobicity, while showing little interaction with molybdenite. The combined evidence from FTIR, XPS, and DFT calculations confirmed that 2-MNA was predominantly chemisorbed on chalcopyrite through S–Cu and N–Cu coordination, thereby effectively inhibiting chalcopyrite flotation. These findings demonstrate that 2-MNA is a promising green depressant, enabling effective separation of Cu–Mo sulfide minerals.