Improvement of the grindability of vanadium-bearing shale and the direct vanadium leaching efficiency of grinded product via microwave pretreatment with particle size classification

Abstract

The total wet extraction technology without roasting will be the mainstream in the field of vanadium extraction from shale under China's strict carbon emission policy. Reducing energy consumption of grinding and improving leaching efficiency are the main directions of efforts. In this study, microwave pretreatment (MT) was used to improve the grindability of vanadium-bearing shale (VBS) and leaching efficiency. Sieving out the particles above 1.5 mm for MT under 2500 W for 4 min and then combining with 0–1.5 mm untreated particles for grinding increases the breakage rate of VBS by 209.0% with a 36.64% reduction in energy consumption. The particles passing 1.5 mm are prone to soft melt due to the hot pot caused by intensification of electromagnetic fields at the junctions of the adjacent particles. This negative effect can be avoided by pre-screening before MT. MT with particle size classification can obtain a 14.2% increasement of vanadium leaching efficiency of grinded products. Simulations and microscopic morphology analyses indicates the temperature gradient between minerals with different dielectric loss properties causes thermal stress with the maximum value at the junction of minerals. It promotes the dissociation of vanadium-bearing minerals and other absorbing minerals, providing more active reaction interfaces for vanadium leaching.