The　adsorption　of　chelating　collector　octyl　hydroxamate　onto　malachite　was　studied　at　various　pH　to　reveal　the　adsorption　mechanism.　Below　pH　6,　a　substantial　amount　of　octyl　hydroxamate　was　consumed　by　copper　ions　in　solution,　leading　to　low　malachite　recovery.　In　the　pH　range　from　6　to　9,　octyl　hydroxamate　mainly　existed　in　the　molecular　form.　The　collector　reacted　with　the　chemisorbed　Cu(OH)(+)　and　Cu(CO3)(2)(2-)　on　the　malachite　surface.　The　octyl　hydroxamate　anion　was　the　predominant　species　above　pH　9.　The　reaction　between　the　anion　and　the　chemisorbed　Cu(OH)(+)　and　Cu(CO3)(2)(2-)　on　the　malachite　surface,　was　responsible　for　flotation　of　malachite.　At　pH　9,　the　maximum　collector　adsorption　and　flotation　recovery　were　achieved,　presumably　as　a　result　of　the　coadsorption　of　octyl　hydroxamate　molecules　and　anions.　Although　Cu(OH)(+)　and　Cu(CO3)(2)(2-)　were　the　predominant　active　species　for　malachite　surface　below　and　above　pH　8.3,　respectively,　and　octyl　hydroxamate　anion　and　molecule　were　the　predominant　species　below　and　above　pH　9,　respectively,　the　same　copper　hydroxamate　chelate　was　formed　on　the　malachite　surface　above　pH　6.