Recovery of tungsten from spent selective catalytic reduction catalysts by pressure leaching

The recovery and purification of vanadium (V) and tungsten (W) from honeycomb-type spent selective catalytic reduction (SCR) catalyst was investigated using an autoclave through a pressure leaching process. Spent SCR catalyst mainly consists of TiO2 and other oxides (7.73% WO3, 1.23% V2O5, etc.). The reaction temperature, NaOH concentration, time, additive concentration, and liquid-solid (L/S) ratio were varied during the leaching process. The optimal reaction conditions were identified for recovery of V and W. The addition of NaOH to Na2CO3 improved the amount of V and W recovered because of the enhancing effect of NaOH in Na2CO3. As the concentration of CaCl2 was increased during the precipitation process in order to separate the recovered V and W, the precipitation percentages of V and W increased, respectively. However, the use of Ca(OH)(2) as the additive reduced the precipitation percentage of W. Therefore, despite full precipitation of V (98.6%), only 7.73% of W was precipitated when 3 equivalents of Ca(OH)(2) was reacted with spent SCR catalyst for 30 min. The remaining Win the leaching solution was reacted with NH4OH to form ammonium tungstate, which was converted to ammonium paratungstate through evaporation. Consequently, V and W could be recovered and separated successfully through the process in this study. (C) 2015 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.