Coal slimes are mainly composed of coal and clay particles.The interaction energies among these particles were calculated using extended DLVO(DERJAGUIN-LANDAU-VERWEY-OVERBEEK)theory and the aggregation mechanisms were analyzed based on the settling experiments for coal-kaolinite and coal-montmorillonite suspensions,respectively,under different conditions of water hardness.The results indicate that for coal-kaolinite suspensions,as the water hardness reaches 10.0mol/L,the coal particles aggregate with each other easily,and then,the coal particles may aggregate with kaolinite particles.However,no aggregation occurs between kaolinite particles.A clay platelet network is formed in coal-montmorillonite suspensions by montmorillonite particles and coal particles are captured into the network.Coal and montmorillonite particles settle completely. Coal slimes are mainly composed of coal and clay particles. The interaction energies among these particles were calculated using extended DLVO (DERJAGUIN-LANDAU-VERWEY-OVERBEEK) theory and the aggregation mechanisms were analyzed based on the settling experiments for coal-kaolinite and coal- montmorillonite suspensions, respectively, under different conditions of water hardness. The results indicate that for coal-kaolinite suspensions, as the water hardness reaches 10.0 mol / L, the coal particles aggregate with each other easily, and then, the coal particles may aggregate with kaolinite particles. Despite, no aggregation occurs between kaolinite particles. A clay platelet network is formed in coal-montmorillonite suspensions by montmorillonite particles and coal particles are captured into the network. Coal and montmorillonite particles settle completely.