NO in flue gas was oxidized into NO2 by ozone in gas-phase first, and then SO2 and NO2 were oxidized by redox reaction between MnO2 and SO2/NO2 and catalyzed oxidation between O-2 and SO2/NO2 in absorption process. Molar ratio of O-2/(SO2 + 0.5NO(x)) in flue gas had a decisive effect on catalyzed oxidation in absorption process, and eventually influenced reaction byproducts, Mn extraction rate and SO2/NOx absorption capability. Results showed that increasing O-2/(SO2 + 0.5NO(x)) enhanced catalyzed oxidation and led to the lower reaction pH. When O-2/(SO2 + 0.5NO(x)) <= 18, SO2 and NOx were mainly oxidized by MnO2 with main products of MnSO4 and Mn(NO3)(2), while when O-2/(SO2 + 0.5NO(x)) >= 18, SO2 and NOx were mainly oxidized by O-2 with main products of H2SO4 and HNO3. Total absorption capability of SO2 and NOx increased with increasing O-2/(SO2 + 0.5NO(x)). Mn extraction rate increased with the increase of O-2/(SO2 + 0.5NO(x)) first and then decreased, the maximum Mn extraction rate of 91% was got when O-2/ (SO2 + 0.5NO(x)) at around 13. Both the SO2/NOx absorption capability and Mn extraction rate could be enhanced by adding rhodochrosite as pH regulator in the case of O-2/(SO2 + 0.5NO(x)) >= 18. (C) 2013 Elsevier B.V. All rights reserved.