In　order　to　improve　the　flotation　separation　of　magnesite　from　dolomite　effectively,　the　organic　regulator,　phenoxyacetyl　chloride　(POC),　was　first　introduced　as　a　selective　depressant　of　magnesite,　with　dodecylamine　(DDA)　as　the　collector.　The　results　of　single　mineral　flotation　showed　that　POC　could　selectively　inhibit　magnesite　but　hardly　affect　dolomite.　The　results　of　reverse　flotation　of　a　synthetic　mixture　of　magnesite　and　dolomite　were　basically　consistent　with　those　of　single　mineral　flotation.　With　DDA　as　the　collector　and　POC　as　the　depressant,　dolomite　floated　selectively　against　magnesite.　Magnesite　and　dolomite　could　be　efficiently　separated　at　pH　8.00　with　a　reagent　scheme　of　0.50　mg/mL　POC　and　30.00　mg/L　DDA.　When　the　mixed　ore　for　the　synthetic　mineral,　grading　42.60　%　MgO　and　2.84　%　CaO,　a　magnesite　concentrate　with　46.85　%　MgO　and　0.45　%　CaO　was　achieved.　Contact　angle,　Zeta　potential,　Fourier　transform　infrared　spectroscopy　(FTIR),　X-ray　photoelectron　spectroscopy　(XPS),　and　DFT　analyses　showed　that　POC　selectively　adsorbed　on　the　surface　of　magnesite,　by　chelating　Mg　on　the　surface　of　magnesite.　The　results　from　the　contact　angle　tests　indicated　that　POC　selectively　reduced　the　surface　hydrophobicity　of　magnesite　in　the　DDA　system.　Besides,　Zeta-potential　measurements　and　FTIR　analyses　revealed　that　the　addition　of　POC　prior　to　DDA　had　no　significant　impact　on　the　adsorption　of　DDA　onto　dolomite;　the　addition　of　POC　strongly　prevented　DDA　from　being　adsorbed　onto　magnesite,　resulting　in　a　significant　difference　in　the　flotation　performances　of　the　two　minerals.　Furthermore,　XPS　analyses　and　DFT　calculations　confirmed　that　the　adsorption　of　POC　on　the　magnesite　surface　could　be　attributed　to　the　interaction　between　the　POC　electron-rich　groups　and　the　Mg　exposed　to　magnesite,　POC　could　be　used　as　a　high-performance　inhibitor　for　the　magnesite　flotation　to　realize　the　decalcificationic.　Based　on　these　experimental　results,　a　possible　model　for　the　flotation　separation　process　of　magnesite　has　been　proposed.