Mechanistic insights into chalcopyrite–molybdenite flotation separation using 4-amino-6-hydroxy-2-mercaptopyrimidine as a selective depressant

The inherent floatability of chalcopyrite and molybdenite, together with the environmental concerns associated with conventional depressants, poses a persistent challenge to their efficient and sustainable separation. Therefore, this study evaluates the potential of 4-amino-6-hydroxy-2-mercaptopyrimidine (AHMM) as an efficient depressant and systematically investigates its role in improving flotation selectivity and regulating interfacial interactions. Micro-flotation experiments showed that at neutral pH and an AHMM concentration of 12 mg/L, the recovery of molybdenite reached 92.91%, whereas that of chalcopyrite was only 7.76%. This large difference corresponds to a selectivity index of 12.48, enabling highly efficient separation of the two minerals. Surface analyses—including zeta potential measurements and surface wettability tests—indicated that AHMM preferentially adsorbed onto chalcopyrite, significantly reducing its hydrophobicity. FTIR and XPS results demonstrated that the S and N atoms of AHMM coordinated with Cu atoms on the chalcopyrite surface, leading to the formation of stable surface complexes. DFT calculations further supported the robust chemisorption of AHMM on the chalcopyrite surface, producing a four-membered chelate via Cu–S and Cu–N coordination. Overall, this study demonstrates that AHMM has significant potential to serve as an efficient and selective depressant for chalcopyrite in Cu–Mo flotation separation processes.