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

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 center dot H2O. Ca3Si2O7 center dot 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.