NH4HSO4　was　used　as　an　activator　to　improve　the　sulfidization　flotation　of　azurite,　with　Na2S　as　the　sulfiding　agent　and　butyl　xanthate　(NaBX)　as　the　collector.　Microflotation,　contact　angle　measurement,　and　adsorption　test　results　indicated　that　NH4HSO4　facilitated　the　sulfidization　flotation　of　azurite,　enhanced　the　adsorption　of　Na2S,　and　improved　the　adsorption　of　NaBX,　which　increased　the　floatability　of　azurite.　Further,　X-ray　photoelectron　spectroscopy　analysis　demonstrated　that　the　combined　use　of　NH4HSO4　and　Na2S　decreased　the　amounts　of　CO32−　and　OH−,　which　resulted　in　high　azurite　surface　hydrophobicity.　In　addition,　NH4HSO4　increased　the　amount　of　copper　sulfide　and　improved　the　sulfidation　of　azurite.　A　potential　model　for　the　reagent　activation　process　was　proposed.　Density　functional　theory　(DFT)　calculations　revealed　that　the　interaction　between　the　Na2S　and　azurite　surface　was　strengthened　by　NH4HSO4　modification.　©　2021　Elsevier　Ltd