Acoustic Cavitation Enhanced Delamination of Technology Critical Metals from Electronic Waste Using Green Solvents

Power ultrasonics is being investigated as a potential technology for the enhancement of technology critical metal (TCM) recovery from electronic waste in green solvents. Deep eutectic solvents (DESs) are an emerging class of ionic liquid with several advantages as a lixiviant. However, the high viscosity of DESs impose mass transport limitations resulting in slow dissolution chemistry. Whilst the application of power ultrasound significantly enhances the etch rate, the driving mechanisms behind this enhancement can be strengthened in less viscous media. In this study, we investigate the dilution of an Ethylene Glycol-Choline Chloride DES with volume fractions of deionized water. By lowering viscosity through tailoring DES water content, we observe strengthened cavitation at the tip of a 20 kHz sonotrode, by acoustic monitoring of bubble collapse shockwave activity. Delamination efficiency of TCMs from Printed Circuit Boards (PCBs) is quantified through surface microscopy of the PCB surface after sonication in each DES-solution. Reducing viscosity through addition of deionized water results in improved delamination rate with over 97 % of the TCM surface removed from the PCB in as little as 150 seconds The results demonstrate the potential for process optimization through solution tailoring for enhanced sonoprocessing.