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

Abstract

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 (R² = 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 η = γ₀ exp(−ktⁿ)μ + ν. 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.