Optimizing vanadium and tungsten leaching with lowered silicon from spent SCR catalyst by pre-mixing treatment

In this paper, the leaching behaviors of vanadium (V), tungsten (W) and silicon (Si) from spent SCR (selective catalytic reduction) catalyst were evaluated and a pre-mix treatment to enhance V-W leaching with low Si leaching at 25°C and atmosphere pressure was developed. The effects of leaching factors were investigated systematically by two orthogonal array experiments, and then experiments with a single variable factor of NaOH concentration and temperature were carried out, respectively. Alkali, especially NaOH, is the best reagent for V and W simultaneous leaching from spent SCR catalyst. Increasing temperature or NaOH/catalyst ratios enhances V and W leaching rates. 68.3% V leaching rate and 50.1% W leaching rate were obtained under an optimal conditions (temperature 100°C, NaOH/catalyst ratio 0.9, L/S 15, stirring speed 900 rpm and time 240 min). However, the W/Si concentration ratio under this condition, as low as 1.4, is unacceptable from the view of separation and economy. A proposed pretreatment process, in which NaOH and catalyst was pre-mixed, decreases time consuming to 20 min and lowers temperature to 25°C but obtains higher W/Si concentration ratio 7.0 and almost the equal leaching rate (67.7% for V and 56.3% for W).