Abstract
The selective dissolution of V and Fe from spent denitrification catalyst (SDC) with oxalic acid was investigated to minimise their environmental effects. The dissolution kinetics of different elements from SDC by using 0.1–1.5 mol L−1 oxalic acid concentration was studied at 60 °C–90 °C. V and Fe were preferentially released (65% and 81%) compared with Al, Ti and W within 5 min due to the redox reactions of oxalic acid. The dissolved fractions of Fe, V, Al, W and Ti increased with the increase of oxalic acid concentration and reaction temperature. The dissolution kinetic experiments were analysed and controlled diffusion with n < 0.5 according to the Avrami dissolve reaction model (R2 > 0.92). The Arrhenius parameters of the Ea values of Ti, W, V, Fe and Al from SDC with oxalic acid were 30, 26, 20, 19 and 11 kJ mol−1, respectively. The obtained Avrami equation of V and Fe was successfully used to predict their leaching behaviour in oxalic acid. Toxicity characteristic leaching procedure revealed that the toxicity risk of V and Fe metals from SDC after leaching with oxalic acid decreased to below 5 mg kg−1 residua. Overall, the leaching residua by oxalic acid indicated its safety for the environment.
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