Metal extraction from ores and waste materials by ultrasound-assisted leaching -an overview

Abstract

ABSTRACT The traditional leaching process is characterized by extensive reaction time, low efficiency, and considerable leaching reagent consumption. It was well demonstrated that using ultrasound could effectively enhance the leaching reaction rate by removing the passivating layer and increasing the mass transfer rates. This improvement would result from bubble cavitation and other mechanical-chemical mechanisms that ultrasounds can generate during ultrasound-assisted leaching (UAL). Thus, these days using UAL for the recovery and recycling of various valuable metals has markedly received attention as an environmentally friendly process. However, surprisingly no comprehensive overview has been provided to focus on various reaction mechanisms through the applications of UAL and deliberate them for nearly two decades. This work has explored various applications of UAL applied for ore and waste processing by a systematic approach to fill this gap. An overview of different mechanisms (mechanical, thermal, sonochemical) based on main ultrasound operating variables (frequency, power, and time) and their level of leaching effectiveness on the leaching metallurgical responses in varied conditions was discussed in detail. It was indicated that the common approach for conducting UAL investigation mainly focuses on improving the leaching efficiency of metals by using single-frequency ultrasound. While analyzing the correlation between ultrasonic cavitation theory and assisted leaching process and exploring the systematic effect of multi-frequency ultrasonic system need to be further clarified in future research. In general, the present work is going to potentially pave the path for understanding UAL and further its development in the future.