Research on the mechanism of mechanochemical activation for enhanced leaching of vanadium-bearing shale: activation kinetics and fluorine adsorption

Vanadium-bearing shale as a strategic resource is an important raw material for extracting vanadium, and the mechanochemical activation can realize the vanadium extraction by full-wet leaching with green, low-carbon and high efficiency. Based on mineralogical research on mineral composition and distribution, mineral embedded grain size distribution, we employ a graded activation process. The mechanism of mechanochemical activation-enhanced dissolution of vanadium-bearing shale is revealed through the relationship between activation kinetics and vanadium leaching as well as the fluorine adsorption process on different minerals surfaces of vanadium-bearing shale. Vanadium-bearing shale is mainly composed of quartz, muscovite, calcite, pyrite, feldspar and apatite. Vanadium with 94.24% exists in muscovite, while the remaining 5.76% exists in oxide. Muscovite is predominantly closely associated with quartz, calcite and organic carbonaceous and tends to be enriched in fine grained, displaying fine disseminated granularity with 0.005-0.06 mm. The grindability order of vanadium-bearing shale is observed as follows: -3 to +2.5 mm < -2.5 to +2 mm < -2 to +1 mm < -1 to +0.6 mm. The activation process of different particle sizes were well evaluated by kinetic equations (<i>R</i> ² = 0.99). The vanadium leaching efficiency has a positive linear relationship with the activation yield at the optimal leaching particle size with -0.6 mm. The vanadium leaching efficiency and activation time can be expressed by equation of <i>η</i> = <i>γ</i> ₀ exp(-<i>kt</i> ^<i>n</i> )<i>μ</i> + <i>ν</i>. The mineral surface of vanadium-bearing shale has a good adsorption of F^- (23.89 mg g^-1) undergoing amorphous phenomena. The order of F^- adsorption capacity is calcite, pyrite, dolomite, muscovite, feldspar, and quartz. The adsorption process of F^- alters the surface potential on the vanadium-bearing shale, and the negative charge on the of muscovite surface increases, while that of pyrite and calcite decreases, which is conducive to the diffusion of H⁺ to the surface of muscovite and away from pyrite and calcite. F^- generates CaF₂ with the surface of calcite and FeF₃ with Fe(iii)-S on the surface of pyrite, hindering and slowing down the dissolution of calcite and pyrite. F^- forms Al-F and Si-F bonds with Si and Al on the surface of muscovite, promoting the dissolution of muscovite.