The release of harmful gases during the combustion of coal due to the presence of ash and sulfur, as a coal associated impurities, has negative effects on the environment as well as on the efficiency of power plants. Removal of ash and sulfur from coal is one of the crucial issues that attract researchers' attention. Several separation techniques were tested for ash and sulfur removal from coal. Bioseparation is one of recently tested methods for removal of sulfur from coal. Therefore, in the current study, bioflotation was used for reducing coal ashes and sulfur using Bacillus subtilis and Paenibacillus polymyxa. Coal-bacteria interaction was investigated using adsorption kinetics, adsorption isotherm, Fourier Transform Infra-Red (FTIR) and zeta potential. Bioflotation results indicated that B. subtilis is better than P. polymyxa for reducing both sulfur and ash content. B. subtilis produces a coal concentrate with a 0.92% total sulfur and 1.95% ash, in comparison to 1.12% total sulfur and 2.65% ash for P. Polymyxa, with a yield exceeds 72%, from feed sample with 3.3% total sulfur and 6.65% ash. (C) 2013 Elsevier Ltd. All rights reserved.