Synergistic extraction-purification strategy: Amine-modified CrOOH composites for selective vanadium adsorption from ultrahigh Cr/V ratio solutions and their green conversion

Selective vanadium extraction from ultrahigh Cr/V ratios systems remains a key challenge, particularly preventing the generation of chromium-containing solid waste, which poses substantial environmental and material-handling concerns. To enable a cleaner vanadium recovery process from chromate systems, polyethyleneimine-functionalized α -CrOOH was designed via a two-step synthesis. The resulting PEI@CrOOH, enriched with abundant –NH + =/–NH 2 + - functional groups, integrates the intrinsic structural stability of α -CrOOH with the strong chelation capability of PEI, achieving a high equilibrium adsorption capacity of 120.18 mg·g −1 for V(V). In both Cr–V binary systems and simulated chromite leaching solutions, PEI@CrOOH exhibits pronounced selectivity toward vanadium over chromium. DFT calculations further elucidate the origin of this selectivity, revealing substantially more negative adsorption energies for H 3 V 10 O 28 3 ⁻ (−478.1 kJ·mol −1 ) compared with those for Cr 2 O 7 2 ⁻ (−214.9 kJ·mol −1 ) and HCrO 4 ⁻ (−141.7 kJ·mol −1 ). The adsorption mechanism is primarily attributed to coordination interactions and redox reactions, with additional contributions from electrostatic attraction and hydrogen bonding. PEI@CrOOH demonstrates excellent reusability, maintaining high adsorption efficiency over multiple regeneration cycles. Moreover, the spent adsorbent can be sustainably upcycled via calcination into high-purity Cr 2 O 3 (99.33%), thus eliminating secondary waste generation. This work presents a technically feasible strategy for the purification and selective extraction of vanadium from chromite leaching solutions.