Vanadium-bearing (V-bearing) shale is an established vanadium resource. In China, it accounts for over 87% of the country’s total vanadium reserve. Meanwhile, vanadium-bearing shales generally contain less than 1% V2O5 – considered a complex low-grade mineral- which makes extraction of vanadium from the shale rather complex and challenging. Presently, blank roasting with sulfuric acid leaching technique is extensively used to extract vanadium from V-bearing shales. However, this technique suffers from low leaching recovery, long leaching time, and high energy consumption, thus cannot sustainably serve as the basis of vanadium extraction. Recent studies have shown that the ultrasonic-assisted method, used in hydrometallurgy during leaching of metals from minerals, can be used to address the above drawbacks owing to its high efficiency. Moreover, fluorine-bearing leaching agents such as CaF2 can significantly improve the vanadium leaching process by enabling efficient breaking of the vanadium-bearing mineral structure, a prerequisite step in vanadium extraction. Nevertheless, most studies have focused on the extraction of vanadium by regular leaching processes, with little being reported about ultrasonic-enhanced vanadium leaching.
Recently, a team of researchers at Wuhan University of Science and Technology: Dr. Bo Chen, Professor Shenxu Bao, Professor Yimin Zhang, and graduate student Sheng Li used a combination of scanning electron microscopy and X-ray diffraction techniques to carefully study the differences between ultrasonic-assisted and regular leaching of V-bearing shale with 0.96% V2O5 grade. They also examined the effects of different parameters, including sulfuric acid concentration, CaF2 content, leaching time and temperature, and ultrasonic power on the vanadium recovery. This approach mainly focused on analyzing the microstructure, chemical phase transformation, and the element distribution of the leaching residues. Their main aim was to develop an alternative and high-efficient method for extracting vanadium from low-grade V-bearing shales. Their research work is currently published in the journal, Separation and Purification Technology.
The research team achieved the optimum recovery of vanadium for both ultrasonic-assisted and regular leaching methods under the conditions of 95°C leaching temperature, 3 wt% CaF2, and 15 vol% sulfuric acid. Overall, the ultrasonic-assisted method outperformed the regular leaching method. For instance, 92.93% of vanadium was leached out at a leaching time of 30 minutes using an ultrasonic-assisted method compared to 87.86% that was obtained with the regular leaching method after 240 minutes. The high performance, in the presence of ultrasound, was attributed to the ultrasonic cavitation, which exposed more active surfaces to the reaction solution by increasing the specific surface area of the V-bearing muscovite particles and reducing the diffusion layer. Furthermore, kinetic fittings results revealed that the leaching process of vanadium from V-bearing shales is mainly controlled by two factors: diffusion through the ash layer and reaction constant of vanadium.
In summary, the study by Wuhan University of Science and Technology scientists presented the new ultrasonic-assisted leaching method as an efficient and sustainable process for extracting vanadium from V-bearing shales. Based on their results, the ultrasonic-assisted method outperformed the regular leaching method with regard to the leaching time, rate, and recovery. In a statement to Advances in Engineering, Professor Shenxu Bao said that the ultrasonic-assisted technique exhibits remarkable advantages that put it ahead as a promising technology for efficient and sustainable extraction of vanadium from low-grade vanadium bearing minerals.
Chen, B., Bao, S., Zhang, Y., & Li, S. (2020). A high-efficiency and sustainable leaching process of vanadium from shale in sulfuric acid systems enhanced by ultrasound. Separation and Purification Technology, 240, 116624.