Leaching of vanadium and tungsten from spent V2O5-WO3/TiO2 catalyst by ionic liquids

Abstract

The V2O5-WO3/TiO2 catalyst has been used for selective catalytic reduction (SCR) of NOx for decades and is named as SCR catalyst. Nine ionic liquids (ILs) were screened to directly leach vanadium and tungsten from the spent SCR catalyst in this work. Effects of leaching temperature, time and catalyst pre-oxidation were evaluated and the pregnant leach solution (PLS) was characterized by nuclear magnetic resonance and Fourier transform infrared to investigate the vanadium leaching route. Results indicate that the basic ILs ([MEA]L, [TMG]L, N2222[L-Pro], N2222[Sar]) and the super acidic IL [Hnmp]HSO4 (pH = −0.43) are effective for V2O5 dissolution, while the neutral ILs and the acidic IL [P(C4H9)3C3H6SO3H][Tf2N] (pH = 0.43) do not work. The vanadium oxide V2O3 cannot be dissolved in the above ILs. Oxidation of the catalyst increases the vanadium leaching efficiency while the particle size of catalyst and temperature have little influence on the leaching efficiency. The vanadium leaching efficiency follows the order of N2222[L-Pro] > N2222[Sar] and [Hnmp]HSO4 > [MEA]L and [TMG]L, with a maximum of about 70%. The dissolved vanadium is in the form of [HnV10O28]n-6 for the basic ILs and [VO2]+ or VO(O2)(OH2)3+ for the acidic IL. These five ILs also have a good ability to leach tungsten from the spent catalyst and the maximum leaching efficiency of tungsten is about 77%.