Microwave-assisted calcination of spodumene for efficient, low-cost and environmentally friendly extraction of lithium

Abstract

To utilize the advantages of microwave-assisted calcination over conventional heating, this work studied the effect of microwave power on phase transformation and leachability of spodumene. X-ray diffraction (XRD) and scanning electron microscope (SEM) were utilized to characterize the phase transformation and structural changes of spodumene calcined by both microwave and conventional heating methods. Results showed that the effect of microwave power on both phase transformation and leachability of spodumene is significant. The optimum lithium recovery through the microwave calcination-acid roasting-leaching process reached 97% at 2.0 kW microwave power, comparable with that of conventional heating. Besides a more rapid, less energy-consuming, and free greenhouse-gas-emission calcination, microwave heating also resulted in lower recovery values of Fe, Na, and Ca in the leaching process, gaining an advantage in downstream purification processes. The microwave temperature profiles of spodumene, and characterization results confirmed that α-spodumene started to transfer into γ- and β-spodumene at around 900 °C.