In　this　study,　the　effects　of　calcium　ions　on　the　flotation　of　malachite　with　octyl　hydroxamate　collector　has　been　investigated　using　micro-flotation,　zeta　potential,　contact　angle,　adsorption,　and　particle　size　measurements.　Although　the　adsorption　amount　of　collector　and　the　hydrophobicity　of　malachite　surface　were　not　influenced　by　the　addition　of　1　×　10−2　mol/L　CaCl2　at　the　optimized　flotation　pH　9,　it　was　found　that　the　malachite　flotation　recovery　was　enhanced　by　the　addition　of　CaCl2　in　the　pH　range　of　6–11.　In　the　presence　of　CaCl2,　energy　barrier　between　the　malachite　particles　and　the　bubbles　were　lower,　leading　to　the　aggregation　of　malachite　particles,　and　the　enhanced　malachite　recovery.　However,　at　pH　>　11,　the　formation　of　Ca(OH)+　and　Ca(OH)2　species　on　malachite　surface　inhibited　its　flotation.　©　2019　Elsevier　Ltd