Three-liquid-phase extraction and separation of V(V) and Cr(VI) from acidic leach solutions of high-chromiumvanadium–titaniummagnetite

A new method by liquid–liquid–liquid three phase system, consisting of acidified primary amine N1923 (abbreviated as A-N1923), poly(ethylene glycol) (PEG) and (NH 4 ) 2 SO 4 aqueous solution, was suggested for separation and simultaneous extraction of V(V) and Cr(VI) from the acidic leach solutions of high-chromium vanadium-titanium magnetite. Experimental results indicated that V(V) and Cr(VI) could be selectively enriched into the A-N1923 organic top phase and PEG-rich middle phase, respectively, while Al(III) and other co-existing impurity ions, such as Si(IV), Fe(III), Ti(IV), Mg(II) and Ca(II) in acidic leach solutions, could be enriched in the (NH 4 ) 2 SO 4 bottom aqueous phase. During the process for extraction and separation of V(V) and Cr(VI), almost all of impurity ions could be removed. The separation factors between V(V) and Cr(VI) could reach 630 and 908, respectively in the organic top phase and PEG middle phase, and yields of recovered V(V) and Cr(VI) in the top phase and middle phase respectively were all above 90%. Various effects including aqueous pH, A-N1923 concentration, PEG added amount and (NH 4 ) 2 SO 4 concentration on three-phase partitioning of V(V) and Cr(VI) were discussed. It was found the partition of Cr(VI) into the PEG-rich middle phase was driven by hydrophobic interaction, while extraction of V(V) by A-N1923 resulted of anion exchange between NO 3 ? and H 2 V 10 O 28 4 ? . Stripping of V(V) and Cr(VI) from the top organic phase and the middle PEG-rich phase were achieved by mixing respectively with NaNO 3 aqueous solutions and NaOH-(NH 4 ) 2 SO 4 solutions. The present work highlights a new approach for extraction and purification of V and Cr from the complex multi-metal co-existing acidic leach solutions of high-chromium vanadium-titanium magnetite