Experiments were conducted using a bubbling reactor to investigate nitrogen oxide absorption in the calcium sulfite slurry. The effects of CaSO
3 concentration, NO
2/NO mole ratio and O
2 concentrations on NO
2 and SO
2 absorption efficiencies were investigated. Five types of additives, including MgSO
4, Na
2SO
4, FeSO
4, MgSO
4/Na
2SO
4 and FeSO
4/Na
2SO
4, had been evaluated for enhancing NO
2 absorption in CaSO
3 slurry. Results showed that CaSO
3 concentration had significant impact on NO
2 and SO
2 absorption efficiencies, and the highest absorption efficiencies of SO
2 and NO
2 could reach about 99.5 and 75.0 %, respectively. Furthermore, the NO
2 absorption was closely related to the NO
2/NO mole ratio, and the existence of NO
2 in flue gas may promote NO absorption. The presence of O
2 in simulated flue gas was disadvantage for NO
x removal because it can oxidize sulfite to sulfate. It was worth pointing out that FeSO
4/Na
2SO
4 was the best additive among those investigated additives, as the NO
2 removal efficiency was significantly increased from 74.8 to 95.0 %. IC and in situ FTIR results suggest that the main products were NO
3 ? and NO
2 ? in liquid phase and N
2O, N
2O
5 and HNO
3 in gas phase during the CaSO
3 absorption process.
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