Study on the decomposition of spent SCR catalyst by Na₂CO₃-NaCl mixed roasting method

The Na₂CO₃-NaCl mixed roasting method was employed to decompose the spent SCR catalyst, and effects of roasting and water leaching process on tungsten extraction rate were investigated in detail. The results revealed that the ratio of sodium carbonate and sodium chloride had a significant effect on tungsten extraction. When the mole fraction of sodium chloride was less than 0.5, the tungsten leaching rate of the roasting slag was higher than the result obtained by pure sodium carbonate roasting method. But when the mole fraction was in the range of 0.5 to 0.8, the result of these two methods were the same. However, negative effects would be produced on the extraction rate of tungsten when the ratio of sodium chloride was further increased. Meanwhile, the mineral phase reconstruction was observed during the roasting process. The original anatase XRD peaks of the spent catalyst weakened or disappeared, and the weaker sodium titanate diffraction peaks appeared. In addition, the leaching rate of tungsten was fast in the water leaching process, which was more affected by temperature than the liquid-solid ratio. Under the conditions of n(NaCl): n(Na₂CO₃): n(Ti)=0.5:1.1:1, roasting at 750 ℃ for 2 h, liquid-solid mass ratio of 8, leaching at 35 ℃ for 1 h, the leaching rate of tungsten can reach 99.1%. Therefore, Na₂CO₃-NaCl mixed roasting method was used to treat spent SCR catalyst with appropriate proportion. This not only improved the extraction rate of tungsten, but also reduced the cost of reagents.