Influence of SiO2 and Al2O3 content on the phase transformation of vanadium-titanium magnetite pellets in the sodium salt roasting process

The influence of SiO 2 and Al 2 O 3 concentrations on phase evolution and vanadium recovery within vanadium–titanium magnetite pellets during the sodium salt roasting process were investigated. The findings revealed that an increase in SiO 2 and Al 2 O 3 levels within the vanadium–titanium magnetite significantly promotes the formation of specific silicates, namely Na 1.75 Al 1.75 Si 0.25 O 4 and Na 3 K(Si 0.56 Al 0.44 )O 16 , as well as aluminates, specifically Na 1.22 Al 11 O 17.11 . The formation of these silicates and aluminates consumes a substantial amount of sodium ions, thereby impeding their diffusion into the interior of vanadium-titanium magnetite particles and suppressing the generation of NaVO 3 and Na 0.79 Fe 0.8 Ti 1.2 O 4 . Additionally, during the sodium salt roasting process, sodium ions migrate from regions of high concentration to those of low concentration via liquid-phase flow and solid-phase diffusion. Elevated SiO 2 content and increased roasting temperature both promote slag formation within the pellets. The slag phase fills the interstitial spaces between particles or coats the particle surfaces, promoting the solid solution of vanadium elements into the slag, which is detrimental to the improvement of vanadium leaching rate. Strategic control of SiO 2 and Al 2 O 3 levels in vanadium–titanium magnetite can significantly enhance vanadium recovery efficiency. For instance, pellets containing 1.7% SiO 2 and 4.25% Al 2 O 3 , amended with 6% sodium carbonate and roasted at 1200 °C for 40 minutes, achieved a vanadium recovery rate of 91.31%.