Ultrasonic-enhanced complete lithium extraction from alkaline roasting slag of spodumene: kinetics and mechanism

Abstract

Lithium extraction from spodumene conventionally requires complex, energy-intensive processes involving high-temperature conversion of α-spodumene to β-spodumene, followed by acid roasting and leaching. Inspired by alkali fusion, we achieved microwave-assisted alkaline roasting of spodumene at only 250 °C, producing water- and acid-soluble salts and thereby substantially reducing the roasting temperature. However, efficient lithium recovery during subsequent leaching remains challenging. Here, we report an ultrasonic leaching (UL) strategy applied to microwave-roasted slag after water washing in a sulfuric acid medium. Under optimized conditions, lithium leaching efficiency reached 99.9%, representing a 27% improvement over conventional leaching (CL). Kinetic analysis revealed that ultrasound reduced the apparent activation energy from 32.61 kJ·mol^-1 (CL) to 20.68 kJ·mol^-1. Mechanistic studies showed that ultrasound disrupts diffusion boundary layers, decreases particle size, and enhances interfacial mass transfer and infiltration, thereby accelerating lithium dissolution. This microwave-ultrasound synergistic strategy provides a highly efficient, sustainable, and environmentally friendly approach for lithium extraction, establishing a promising paradigm for process intensification in green hydrometallurgy.