Optimizing vanadium extraction from shale leachate using salicylhydroxamic acid-tri-n-octylmethylammonium

Vanadium (V) extraction from V-bearing shales typically involves direct leaching with sulfuric acid, resulting in highly acidic leachate containing multiple impurity elements, which complicates the V extraction process. Ionic liquid (IL) extraction methods have proven challenging due to the presence of V in its cationic form in the leach solution, while ILs generally function as anion-exchange extractants. In this study, the STOMAC system (salicylhydroxamic acid (C7H7NO3) to V molar ratio of 1) was proposed as an innovative solution for extracting V from this complex leachate. Key parameters affecting the extraction efficiency, including modifier selection, C7H7NO3 concentration, solution pH, phase ratio, and reaction time, were evaluated. Experimental results demonstrated that STOMAC exhibits excellent extraction performance, with approximately 99.29% of V extracted through a three-stage countercurrent extraction process under optimal conditions. Notably, the coextraction of major impurities such as aluminum (Al), magnesium (Mg), iron (Fe), and phosphorus (P) remained below 5%. The extraction mechanism of V and the preparation of STOMAC were further elucidated through Fourier transform infrared spectroscopy (FT-IR), proton nuclear magnetic resonance spectroscopy (1H NMR), and electrospray ionization (ESI) analyses. The data revealed that the hydrogen (H) atom of the salicylhydroxyl group coordinates with TOMAC in a 1:1 ratio, while the hydroxamic group forms a 1:1 coordination with the V ion. These results suggest that the STOMAC extraction system effectively recovers V from acidic leachate without necessitating pH adjustment, offering a more streamlined and cost-effective extraction process with reduced reliance on additional chemical agents.