Spent V2O5-WO3/TiO2 catalyst processing for valuable metals by soda roasting-water leaching

In this paper, extraction of vanadium and tungsten from spent selective catalytic reduction (SCR) catalyst by a soda roasting process was investigated. The leaching efficiency of tungsten significantly increased with the increases in Na2CO3 addition, roasting time and temperature. A leaching efficiency of tungsten was achieved with 92% when the spent SCR catalyst was roasted using 10 equivalent ratio of Na2CO3/total wt% of V2O5 and WO3 under the following conditions: particle size of feedstock, < 106 um; roasting temperature, 1073 K; and roasting time, 120 min. Of particular note, increasing the leaching efficiency of tungsten was closely related to the degree of phase transition from TiO2 anatase to its rutile phase and suppression of formation of CaWO4 by increasing the amount of Na2CO3 addition. On the other hand, the leaching efficiency of vanadium was seldom affected by the soda roasting variables, and showed almost constant around 40% throughout the experimental results. This was presumably due to the formation of calcium vanadate by the reaction with CaO in the feedstock. Furthermore, it can be assumed that the leaching efficiency of vanadium was determined by the content of calcium in the feedstock.