Abstract: The addition of Na₂CO₃ in the process of sodium roasting of vanadium-bearing siliceous shale can promote the oxidation and leaching of vanadium. The promotion effect of Na₂CO₃ was investigated based on promotion effect by chemical composition analysis， XRD and SEM-EDS of roasting products and leaching residue from oxidation roasting with composite additive. The results showed that:① When the mass ratio of NaCl+Na₂CO₃ （3∶2 of mass ratio） to the raw material was 10%， the roasting temperature was 800 ℃， the roasting time was 180 min， the liquid-solid ratio was 10 mL/g， the leaching temperature was 80 ℃ and the leaching time was 120 min（stirring speed is 600 r/min）， the optimal leaching rate of vanadium was 84.96%.② During roasting， because of the destruction of Al-O octahedral lattice， the muscovite and illite in the raw materials were transformed into the melt particles containing Na， K， Al， Si and O. The addition of Na₂CO₃ increases the basicity of raw materials， enhances the reactivity of quartz and produces porous particles by co-melting with molten particles. ③With the addition of Na₂CO₃， the micropore structure produced by co-melting of melt particles and quartz and the gas channel formed by feldspar filling in the melt particles during roasting， enhanced the diffusivity of O₂， increased the contact probability with low-valent vanadium in ore， and accelerated the process of vanadium oxidation， and increased the oxidation roasted effect of vanadium.

Key words: Siliceous shale, Composite additive, Leaching rate, Molten particles, Microporous structure