Synergetic strengthening mechanism of ultrasound combined with calcium fluoride towards vanadium extraction from low-grade vanadium-bearing shale

Abstract

The effect and mechanism of ultrasound and CaF2 on vanadium leaching from vanadium-bearing shale were investigated systematically. In consideration of the enhancement for vanadium recovery, the combination of ultrasound and CaF2 (66.28%) exerts more evident effects than ultrasound (26.97%) and CaF2 (60.35%) alone, demonstrating the synergetic effect of ultrasound and CaF2. Kinetic analysis manifests that the product layer diffusion controls vanadium leaching in ultrasound system without CaF2, however product layer diffusion and interfacial reaction is the rate-controlling step for vanadium leaching in other three leaching systems. The combination of ultrasound and CaF2 notably decreases the activation energy (Ea) from 62.03 to 27.61 kJ/mol, nevertheless individual CaF2 only reduces the Ea to 50.70 kJ/mol. X-ray diffraction and fourier transform infrared spectrometer analyses show that the decomposition degree of the vanadium-bearing mica structure is the most significant in ultrasound and CaF2 system, proving the highest release degree of vanadium. Specific surface area and pore distribution combined with scanning electron microscope analyses reveal that the action of ultrasound and CaF2 would provide higher specific surface area, more abundant pores structure and cracks for the particles, which further prompts the rapid diffusion of H+, F− and HF, and achieves the conspicuous improvement of vanadium leaching recovery.

Keywords

• Vanadium-bearing shale
• Ultrasound
• CaF2 addition
• Synergetic effect
• Leaching kinetics