A molecular extraction process for vanadium based on tandem selective complexation and precipitation

Recycling vanadium from alternative sources is essential due to its expanding demand, depletion in natural sources, and environmental issues with terrestrial mining. Here, we present a complexation-precipitation method to selectively recover pentavalent vanadium ions, V(V), from complex metal ion mixtures, using an acid-stable metal binding agent, the cyclic imidedioxime, naphthalimidedioxime (H₂CID^III). H₂CID^III showed high extraction capacity and fast binding towards V(V) with crystal structures showing a 1:1 M:L dimer, [V₂(O)₃(C₁₂H₆N₃O₂)₂]^2-, 1, and 1:2 M:L non-oxido, [V(C₁₂H₆N₃O₂)₂] ^̶ complex, 2. Complexation selectivity studies showed only 1 and 2 were anionic, allowing facile separation of the V(V) complexes by pH-controlled precipitation, removing the need for solid support. The tandem complexation-precipitation technique achieved high recovery selectivity for V(V) with a selectivity coefficient above 3 × 10⁵ from synthetic mixed metal solutions and real oil sand tailings. Zebrafish toxicity assay confirmed the non-toxicity of 1 and 2, highlighting H₂CID^III's potential for practical and large-scale V(V) recovery.