Abstract：In order to study the microscopic characteristics and sedimentation effect of different particle size of raw coal after adding flocculants, slime flocs structure were observed by optical microscope, the area and perimeter were extracted by Image J software, and the floc size, fractal dimension, floc density and flocculation strength were valued. The settling velocity and the supernatant transmittance were taken as macroscopic factors to compare the effect of different flocs. The results show that the maximum sedimentation velocity of coal particles with particle size of 0.250~0.125 mm is 78.40 cm/min and the maximum of supernatant is 83.6% under the condition of 200 g/t dry coal flocculant. The maximum floc strength is 280.01 ×10^-19 N, the minimum density of floc is 1 033.95 kg·m³, and the minimum value of floc fractal dimension is 1.361.

Keywords: floc size; fractal dimension; floc density; floc strength; sedimentation