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

Abstract

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.

Fig. 1. Cyclic imidedioximes and metal binding mode.

Glutarimidedioxime (H₂CID^I), phthalimidedioxime (H₂CID^II), and naphthalimidedioxime (H₂CID^III).

Fig. 2. Crystal structures of V-CID^III complexes.

Asymmetric units. a 1:1 V-CID^III complex, 1. b 1:2 V-CID^III complex, 2. Unit cell configurations. c 1:1 V-CID^III complex, 1. d 1:2 V-CID^III complex, 2. Countercations omitted for clarity. (Inset: bond lengths between the metal ion and O and N donor atoms).

Fig. 3. Tandem complexation-precipitation technique for recovery of vanadium.

a Structures of V(V) and H₂CID^III. b 1:1 and 1:2 V-CID^III complexes 1 and 2. c neutralized and π-π stacked V-CID^III complexes. V(V) recovery from single-metal aqueous solutions. d Influence of pH on V(V) complexation and precipitation; In each case, 0.05 g (0.25 g l⁻¹) of H₂CID^III was exposed to 20 mg l⁻¹ V(V). e The extraction isotherm of V(V) on H₂CID^III; In each case, 0.05 g (0.25 g l⁻¹) of H₂CID^III was exposed to V(V) for 12 h at 25 °C (Inset shows ¹H NMR of pristine H₂CID^III, 2 and 1 obtained from samples in isotherm with q_e of 80 mg g⁻¹ and 200 mg g⁻¹, respectively). Source data for (d) and (e) are provided as a Source Data file.

Fig. 4. V(V) recovery from mixed-metal aqueous solutions.

a Control experiment of H₂CID^III in the recovery of several metal ions from aqueous solutions. Qualitatively, color change of solutions depict complexation. Precipitation of solely the V sample is observed. In each case, 0.01 g of H₂CID^III was exposed to 1 mg l⁻¹ respective metal solutions for 12 h at 25 °C. b Quantitatively, extraction performances of H₂CID^III for various metals from simulated mixed solutions containing V(V) and excess Fe(III), Cr(III), Cu(II), Ni(II), and Zn(II). Source data for (b) are provided as a Source Data file.

Fig. 5. Spectroscopic analyses and theoretical computations via DFT methods.

a Potentiometric titration curves of 1:2 and 1:1 V-CID^III complexes. b FT-IR spectra of pristine H₂CID^III (0), Na⁺-form (1) and H⁺-form (2) 1:2 V-CID^III complexes, and Na⁺-form (3) and H⁺-form (4) 1:1 V-CID^III complexes. c E_complexation and electrostatic potential maps (EPM) of 1:1 V-CID^III complex. d E_{neutralization} and EPM of neutral 1:1 V-CID^III complex. e E_complexation and EPM of 1:2 V-CID^III complex. f E_{neutralization} and EPM of neutral 1:2 V-CID^III complex. Source data for (a) are provided as a Source Data file.

Fig. 6. V(V) extraction from real waste source.

a Selective recovery of V(V) with H₂CID^III from oil sands tailings containing a series of metal ions. b Images of samples utilized and obtained during the extraction process. Source data are provided as a Source Data file.