Solvent extraction mediated by specific complexation of acetate ions for efficient separation of vanadium and chromium

The chemical similarity between vanadium and chromium poses significant challenges for the selective extraction of V(IV) from Cr(III)-containing solutions to prepare high-purity vanadyl sulfate electrolyte. In this study, with EHEHPA employed as the extractant and the extraction equilibrium pH maintained at 2.5, the introduction of 1.00   mol/L sodium acetate into the solution effectively suppressed the extraction of Cr(III) while preserving the efficient extraction of vanadium achieving a separation factor of 29482. This introduction of acetate ion not only significantly enhanced the separation of vanadium and chromium but also effectively mitigated the precipitation of sodium salts at lower temperatures. Furthermore, after pretreatment of the water-leaching solution of sodium-roasted vanadium slag, extraction was carried out under the sodium acetate concentration of 1.00   mol/L, and the vanadyl sulfate electrolyte containing 2.12   mol/L of vanadium and only 2.17   mg/L of chromium was obtained after stripping. At low sodium acetate concentrations (≤ 0.05   mol/L), Cr(III) predominantly exists as [Cr(H 2 O) 6 ] 3+ , while at higher sodium acetate concentrations (e.g., 1.00   mol/L), Cr(III) primarily exists as [Cr(CH 3 COO) 2 (H 2 O) 4 ] + . Density functional theory calculations show that acetate ion readily complexes with Cr(III), forming a stable water-soluble complex. This complexation inhibits the extraction of Cr(III) by EHEHPA and enables efficient separation of vanadium and chromium.