The effects of ultrasonic waves on the flotation of calcite, barite and quartz have been investigated in the case of single and mixed minerals. In the case of single minerals, ultrasonic treatment has a positive effect in the flotation performance of calcite and barite, while showing a negative effect in the case of quartz. Similar results were obtained in the case of mixed minerals. This has been attributed to the difference between collector adsorption mechanisms characterised by infrared spectroscopy, Chemical adsorption takes place on calcite and barite whereas plysical adsorption takes place for quartz. (C) 2004 Institute of Materials, Minerals & Mining Published by Maney on behalf of the Institute in association with AusIMM. Manuscript received 30 October 2003; accepted in final form 1 June 2004.