Collectorless flotation separation of molybdenite from complex sulfide minerals employing a bi-carbonyl depressant

•Acetoacetamide (CSD2) is used as a selective depressant to realize the flotation separation of sulfide minerals.•The collectorless flotation with only CSD2 reduces the cost and simplifies the process.•CSD2 can expand the recovery gaps between molybdenite and chalcopyrite, galena, and pyrite to 60–80%.•–C=O in CSD2 molecule realizes the stable adsorption onto the surfaces of chalcopyrite, galena and pyrite.•–NH2 in CSD2 molecule bonds to S2– through hydrogen bonding, improving its selectivity and surface hydrophilicity.