Phase transformations of vanadium recovery from refractory stone coal by novel NaOH molten roasting and water leaching technology

Abstract

In this study, a novel NaOH molten roasting and water leaching technology, an eco-friendly process with good selectivity and good availability, was investigated for vanadium recovery from refractory stone coal. In addition, the phase transformations during the vanadium recovery process were also studied. During the NaOH molten roasting process, the monoclinic crystalline structure of muscovite (K(Al,V)₂[Si₃AlO₁₀](OH)₂) was converted into the orthorhombic crystalline structure of Na₂SiO₃ and the tetragonal crystalline structure of gehlenite (Ca₂Al₂SiO₇); this could promote the liberation and recovery of vanadium. During the water leaching process, the tetragonal crystalline structure of gehlenite (Ca₂Al₂SiO₇) was converted into the monoclinic crystalline structure of Ca₃Si₂O₇·H₂O. Ca₃Si₂O₇·H₂O, a kind of C–S–H gel, produced during the water leaching process probably covered the surface of the roscoelite and thus prevented effective vanadium recovery from roscoelite.