Leaching behavior of vanadium from spent SCR catalyst and its immobilization in cement-based solidification/stabilization with sulfurizing agent

To understand the potential leaching toxicity of V in spent SCR catalysts for human and environment, the leaching behavior of V in spent V2O5-WO3/TiO2 SCR catalysts before and after cement stabilization/solidification (S/S) process was investigated. The results showed that the cement mixing ratio, curing time and solidifying agents (Na2S and sodium diethyl dithiocarbamate (DDTCNa)) obviously affect the leaching ability of V in spent SCR catalysts. The leaching amount, leaching concentration and leaching rate of V in original spent SCR catalyst are 137.98 mg/kg, 13.79 mg/L and 1.82%, respectively. After the spent SCR catalyst was solidified with cement and cured for 28 days, the leaching concentrations of V in catalyst-cement solidified waste are 2.27 mg/L for 30% of cement addition and 0.14 mg/L for 70% of cement addition, respectively. Increasing cement mixing ratio and curing time could decrease the leaching concentrations of V in the cement solidified waste by affecting the generation of V5+-bearing species, which was identified by XRD, BET, SEM and FTIR. The heavy metal V could be immobilized through the formation of VO43--bearing compounds in hydrating cement matrix. Evaluation on the leaching concentrations of V after adding Na2S and DDTCNa in cement solidified waste revealed that Na2S and DDTCNa are capable of reducing leaching concentrations of V from 6.25 mg/L to 5.74 mg/L and 4.65 mg/L, respectively. DDTCNa showed a better solidification performance for V compared to Na2S.