In this study, effects of simultaneous ultrasonic treatment on flotation of original and aged hard coal slimes were investigated with aiming to recover more combustible and good quality products. Conventional and ultrasonically assisted flotation tests of original and aged coal slimes were performed by using Montanol-531, a special coal flotation reagent, at variable dosages. The results of the batch flotation tests revealed that simultaneous ultrasonic treatment increased combustible recovery and lowered ash values of concentrates compared to the conventional flotation conditions despite using similar reagent dosages. These results were also verified by testing some physico-chemical properties of the samples, i.e. temperature, pH, oxidation-reduction potential, and zeta potential. Finally, it is concluded that a thorough surface cleaning by cavitation due to power ultrasound might improve the flotation recovery compared with the conventional flotation conditions, even though very slight changes were also observed in some physico-chemical properties of the treated samples. (C) 2011 Elsevier Ltd. All rights reserved.