Abstract: order to better achieve the flotation decalcification of magnesite， the crystal structure， cleavage surface， minerals and the interaction model with common flotation reagents of magnesite， dolomite and calcite were simulated by Materials Studio （MS） software based on density functional theory. The energy band structure， density of states， surface energy of the three minerals， the frontier orbital ，as well as interaction energy between the minerals and common flotation reagents were calculated， which helps to study flotation mechanism of calcium-magnesium carbonate minerals from microscopic view. Theoretical studies indicated that magnesite， dolomite and calcite are all insulators. Sodium hexametaphosphate and water glass are interacted with these three minerals easily， compared with sodium oleate and dodecylamine. The complete cleavage surface of magnesite， dolomite and calcite are {104}plane， {110}plane and {104}plane respectively. The calcium ions and magnesium ions of these three minerals are chemically adsorbed with the carbonyl oxygen of sodium oleate， and the interaction with dodecylamine is the physical adsorption accompanied with the formation of N-H…O hydrogen bonds， indicating a selectivity interaction between dodecylamine and calcium magnesium carbonate minerals in flotation. The speculative results of the first principles are basically verified by the pure minerals flotation experiments， which indicates that the first-principles has guiding significance for the selection of flotation separation agents and its mechanism research.

Key words: Magnesite, Dolomite, Calcite, MS simulation, Flotation