Mineralogical characterisation of vanadium slag under different treatment conditions

Synthetic vanadium slags were melted at 1673 K and then cooled to a predetermined temperature at different cooling rates. The mineralogical phases and crystallisation behaviour were investigated based on optical microscopy, SEM, EDS and XRD analyses. The results show that spinels and silicates were the major phases in the complex vanadium slag samples, and V is enriched in the spinel phases, i.e. FexV3-xO4 and Mg-x(V,Ti)(3-x)O-4. The apparent diameter of spinel crystal grains decreases with increasing cooling rate, e.g. from 14 to 5 mm at 1523 K. Crystal grain size increases significantly with increasing holding time. It is also found that the grain sizes of spinels at higher temperatures, 1573 and 1623 K, are considerably smaller than at lower temperatures, 1473 and 1523 K. At lower temperature, large blocked spinel crystals between grey silicate phases are formed, whereas there only a few smaller blocked spinels when performed at higher temperature. Better control of the process cooling parameters will benefit vanadium slag quality.