Selective depression of chalcopyrite by 2-mercapto-5-benzimidazolesulfonic acid sodium salt for the flotation separation of Cu–Mo sulfides

The flotation separation of chalcopyrite from molybdenite is hindered by their comparable floatability in the presence of collectors. In this work, 2-mercapto-5-benzimidazolesulfonic acid sodium salt (MBS) was proposed as a selective chalcopyrite depressant in Cu–Mo flotation using kerosene as the collector. Micro-flotation tests showed that 8 × 10 −5 mol/L MBS restricted chalcopyrite recovery to below 15 % over the pH range of 4.0–8.5, while molybdenite recovery remained above 94 %. For a 1:1 mixed-mineral feed at pH 7.0, MBS produced a concentrate assaying 54.31 % Mo with a Mo recovery of 95.81 % and a Cu recovery of 2.33 %, outperforming sodium sulfide and sodium thioglycolate applied at the same dosage. Bench-scale flotation of a real Cu–Mo bulk concentrate further validated this selectivity, where MBS returned a higher molybdenum recovery and grade and a much lower copper recovery than STG at an identical dosage. Contact angle, zeta potential, adsorption capacity, AFM, and Raman analyses consistently revealed that MBS preferentially accumulates on chalcopyrite, rendering its surface hydrophilic and weakening the hydrophobizing effect of kerosene, whereas the molybdenite basal plane is barely affected. ToF-SIMS imaging coupled with principal component analysis identified the Cu-bearing organic fragment C 7 H 4 N 2 S 2 O 3 Cu − exclusively on chalcopyrite, indicating the formation of Cu–MBS surface complexes, while no Mo–organic species were detected on molybdenite. DFT calculations further showed that the exocyclic S atom of MBS bonds to surface Cu atoms of chalcopyrite (112) (adsorption energy: −127.61 kJ/mol; Cu–S bond: 2.269 Å) through Cu 3d–S 3p orbital hybridization, whereas its interaction with molybdenite (001) is weak physisorption (−5.10 kJ/mol). These findings suggest that MBS is a promising alternative to conventional sulfide depressants for the flotation separation of Cu–Mo sulfides.