The variables affecting flotation during ultrasonic preconditioning, i.e. pulp concentration, particle size and density, temperature, pressure, as well as ultrasound frequency and amplitude, were studied. An ultrasonic process for the batch flotation of sulphide ores from the Merensky reef in South Africa was designed to improve flotation performance, by selectively altering the surface properties of the target mineral particles. After ultrasonic excitation, the floatability of the sulphides improved significantly, and the silicates were also depressed to some extent. Compared to mechanical conditioning, ultrasonic radiation can improve the flotation rate, value grades and recoveries and reduce the dosages of flotation reagents appreciably.