Enhanced metal recovery using ultrasound assisted leaching (UAL). An overview

Cavitation is one of the major effects of UAL, associated with a variety of phenomena and physical aspects such as chemical, mechanical, and thermal. Cavitation, categorized as an unconventional metal extraction technique, has lately been brought into the field of extractive metallurgy. The past decade has been marked by fundamental advances in leaching efficiencies and reduced reagent consumption with fast reaction kinetics. However, it needs further improvement for carbon neutrality and a sustainable environment, which could be achieved through the enhanced cavitation mechanism. Therefore, the current review focuses on the latest frontiers of conventional and unconventional leaching techniques, with the addition of hydrodynamic and ultrasound-based cavitation systems. By combining the two systems, we may reduce the processing time, energy, and reagents needed to increase the leaching rates of the target metals from various resources on a large scale. This study also observed a resurgence in this field through in-depth discussions on key parameters such as frequency, power, time, temperature, and particle size using kinetic models. Our study found that the particle size, agitation rate, and standing wave formation during UAL operation attract bare attention, which hinders the extraction rates. In addition, we found that dual-frequency ultrasonic transducer reactors effectively enhance extraction rates. The discussion covers additional parameters related to process intensification, such as the type of ultrasound device, vessel position, characteristics of the transmitting liquid, irradiation mode, and the ultrasound probe's horn immersion depth. In addition, we survey future research directions for worthwhile applications that lay a theoretical foundation for further study in this area.