An investigation of spark discharge parameters for material processing with high power ultrasound

High power ultrasound (HPU) generated using pulsed-power techniques provides an alternative method for treating ores and minerals prior to extraction processes and for the comminution of waste materials as part of a recycling process. In an earlier publication [Wilson, M.P., Balmer, L., Given, M.J., MacGregor, S.J., Mackersie, J.W., Timoshkin, I.V., 2006. Application of electric spark generated high power ultrasound to recover ferrous and non-ferrous metals from slag waste. Minerals Engineering 19, 491–499], preliminary results using the HPU technique to treat stainless steel slag and waste bottle glass were reported. This paper describes further work performed on stainless steel slag to determine the likely energy costs associated with HPU processing. In industrial applications of HPU it is important to optimise the parameters of the high-voltage (HV) spark discharge causing the shock wave in the working liquid to maximise the efficiency of the treatment. However, because of the high intensity of the shock wave it is difficult to measure its output close to the HPU source. Experiments have therefore been performed using Pinducer sensors to measure the pressure waves produced by the source at distances relatively far from the spark discharge. These measurements made in the far field have been correlated with the electrical energy provided to the discharge and treatment rates for stainless steel slag and bottle glass obtained under identical conditions.