Hydrodynamic parameters play an important role in flotation efficiency. In the present work, the effects of some key hydrodynamic factors such as impeller speed (600, 700 rpm), impeller off-bottom clearance (0.3H, 0.4H), solids percent (12%, 14%), frother type (Pine oil and methyl isobutyl carbinol (MIBC)) and their concentrations (140, 170 ppm) on the flotation performance of coarse coal particles were investigated using factorial experimental design. The DX8 software was used to analyze the results of the experiments. According to DX8 software, it is concluded that until 700 rpm, the effects of the studied parameters follow the order: impeller off-bottom clearance > impeller rotational speed > frother concentration > the interaction between impeller off-bottom clearance and impeller speed. But for higher impeller speeds, the impeller rotational speed has the most effects. The positive effect of impeller speed before 700 rpm (i.e. 97397.38 < Re < 119589.22, 1.21 < Fr < 1.53 and 0.0035 < C-a < 0.0038 for 0.01226 < mu(p) < 0.01299) and its negative effect beyond (i.e. Re > 113609.61, Fr > 1.53 and 0.0033 < C-a < 0.0035 for mu(p) = 0.01299) concluded that the optimum value for impeller speed is 700 rpm. Also, it was concluded that the recovery of coarse coal particles is increased by increasing pulp solids percent because of increasing medium viscosity. (c) 2012 Elsevier Ltd. All rights reserved.