High efficient vanadium extraction from vanadium slag using an enhanced acid leaching-coprecipitation process

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• V in V slag was efficiently extracted by a two-stage leaching process. • 98.52% of V leaching efficiency was obtained via sodium roasting-water leaching and acid leaching. • The stable V in spinel was converted into amorphous V-Fe compound by hydrolysis precipitation. • This method can provide technical and theoretical support for efficient V extraction from V slag. Vanadium slag (VS) is a by-product of vanadium titanium magnetite BOF steelmaking process and becomes an important material for vanadium products preparation. Sodium roasting-water leaching is a mainstream process for industrial production, but the water leaching residue (WLR) usually remains 1.0 wt.% to 3.0 wt.% V 2 O 5 , which still has value for recycling extraction of vanadium. In this research, a two-stage leaching process was proposed for high efficient vanadium extraction. The first stage leaching was sodium roasting-water leaching for VS and the second stage leaching was sulfuric acid leaching for WLR. As a result, the total leaching efficiency of vanadium can reach as high as 98.52%, which was 7.72% higher than that of conventional water leaching efficiency of vanadium (90.80%). The mechanism analysis indicates that the CaNaFe 2 Si 4 O 12 and NaFeSi 2 O 6 water-insoluble phases formed and covered on (Mn,Fe)(V,Cr) 2 O 4 spinel surface during roasting, hindering vanadium oxidation and dissolution. The structures of wrapping phases and spinel can be effectively destroyed by acid leaching, releasing vanadium in WLR. By using hydrolytic precipitation of iron ions in acid leachate, 99.78% of vanadium can be recovered as V-Fe precipitation slag, which contains 6.83 wt.% V 2 O 5 and can be cycled back to sodium roasting process. The V-Fe slag belongs to amorphous precipitation, illustrating that residual vanadium in WLR can be changed to unstable compound by acid leaching and hydrolysis precipitation, which makes vanadium easier to extract during sodium roasting-water leaching process. This research has the advantages of enhanced reuse of V resource in the WLR, achieving a high V recovery. The short process has a strong adaptability and can provide technical support for efficient V extraction from VS.