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 co-extraction 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.