Recovery of Tungsten and Vanadium from Spent Selective Catalytic Reduction Catalysts by Soda Roasting: A Mechanistic Study

This research investigated how soda roasting, which alters the roasting temperature and sodium carbonate concentration, recovers tungsten and vanadium from used selective catalytic reduction (SCR) catalysts. The ideal sodium carbonate content and roasting temperature were determined to be 800 °C and 30 wt%, respectively. Under these circumstances, tungsten and vanadium recoveries were 82.63% and 90.07%, respectively. In order to understand the roasting process, the compositions and morphologies of the original catalyst and specimens after roasting were examined by X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy. In addition, the thermodynamic parameters associated with this process were calculated using the HSC 6.0 program to confirm compositional changes during roasting, the result shows that the chemical reactions among vanadium, tungsten, titanium and sulfur with sodium carbonate have priority in this system, as V 2 O 5 = SO 3 > WO 3 > TiO 2 ; And the phases formation of vanadium and titanium are different at different temperatures and the amount of sodium carbonate, such as Na 2 V 2 O 6 , NaVO 3 , Na 3 VO 4 , VO 2 , Na 2 O* TiO 2 , Na 2 O* 3TiO 2 , 4Na 2 O* 5TiO 2 , and so on. Therefore, the recovery of vanadium and tungsten is significantly influenced by the other catalyst components as well as the reaction conditions. Based on this combination of experimental study and theoretical calculations, a technique for recovering tungsten and vanadium from spent SCR catalysts by soda roasting is suggested.