<p>The impacts of particle size of vanadium–chromium slag (VCrS) on calcified vanadium extraction process were poorly understood. VCrS with different particle sizes VCrS-<i>y</i> (<i>y</i> is the value of D₉₀, 28.06–569.92 μm) were prepared to investigate the phase transformation during calcium roasting and acid leaching, along with separation efficiency of vanadium and chromium. The results indicate that after calcium roasting at 850&#xa0;°C, the phases of roasted slag were basically the same, but more Fe₂O₃ and a few chromium–iron spinel were detected in VCrS-569.92. The morphology of roasted slags became clearer, more dispersed and distinguishable with decreased particle size as <i>y</i> from 569.92 to 28.06 in VCrS-<i>y</i>. When roasting temperature was not higher than 850&#xa0;°C, the continuous refinement of VCrS was beneficial to improve the leaching rate of vanadium and reduce that of chromium. Since temperature was 900&#xa0;°C, the vanadium leaching rate of VCrS-336.23 was the highest, it decreased with the continuous refinement of VCrS, and all chromium leaching rate below than 0.1%. The leached tailing of VCrS-569.92 exhibited a little peaks of spinel phase which also observed in micromorphology, moreover, it possessed semi-encapsulated block structure with pyrovanadate phase located on the outer layer and solid solution phase in the interior.</p> Graphical Abstract <p></p>