Reaction mechanism of NOx removal from flue gas with pyrolusite slurry

• A wet NOx removal process use pyrolusite slurry as absorbent.
• NOx was oxidized to NO3- by MnO2 and O2 in liquid phase.
• NOx removal efficiency depended on molar ratio of NO2 to total NOx.
• NOx removal efficiency constant at 60% and Mn extraction rate reah 90%.
• Prepared Mn(NO3)2 product meets the national industry grade standards.

Pyrolusite slurry was used as absorbent to remove NOx from flue gas. Reaction mechanism of NOx removal was theoretically analyzed based on E-pH diagram of Mn–NOx–H2O system and then verified by experiments via both the qualitative and quantitative analysis of reaction products. Main reaction and byproduct were also investigated in depth. Results showed that NOx   in flue gas dissolved into liquid phase first and then were oxidized into NO3- by MnO2 and O2. NO2 was more easily removed than NO because of its high solubility. NOx removal efficiency was depended strongly on the molar ratio of NO2 to NOx (NO2/NOx ratio). When NO2/NOx ratio at 75%, NOx removal efficiency remained between 60% and 64% within 11 h and manganese extraction rate reached 92%. Manganese nitrate, meeting the needs of national industry grade standards, could be produced using purified absorption solution.