A high-efficiency and sustainable leaching process of vanadium from shale in sulfuric acid systems enhanced by ultrasound

Abstract

A major source of vanadium recovery and also the raw material of this research is the vanadium-bearing (V-bearing) shale. The main purpose of the study is to capture the difference between the ultrasonic-assisted and regular leaching of vanadium from roasted V-bearing shale, having a V2O5 grade of 0.96%. In this work, the effects of various factors such as ultrasonic power, sulfuric acid concentration, amount of CaF2, leaching time and leaching temperature on the leaching recovery of vanadium were investigated by the comparison of the two methods. The results showed that the optimum leaching recovery of vanadium for regular and ultrasonic-assisted leaching method were both achieved under the conditions of 15 vol% sulfuric acid, 3 wt% CaF2 and leaching temperature 95 °C. It was clearly found that the leaching recovery of vanadium can be increased from 87.86% to 92.93%, furthermore, the leaching time can be reduced by as much as 87.5% (240 min vs 30 min) in the presence of ultrasound. The enhancement of ultrasound on the leaching rate and ratio was mainly ascribed to that ultrasonic cavitation can increase the specific surface area and renew the active surface of the V-bearing muscovite particles involved in the leaching reaction. The kinetics analysis proved that the vanadium leaching process is both controlled by diffusion through the product/ash layer, and the reaction constant (kd) of vanadium leaching process with ultrasound is much higher than that without ultrasound, promoting vanadium release and accelerate the diffusion rate from the shale. Therefore, ultrasonic-assisted leaching method may be a potential and sustainable technique for increasing the leaching efficiency of vanadium from low-grade V-bearing shale.