Enhanced NO_x absorption in flue gas by wet oxidation of red mud and phosphorus sludge

The environmental problem caused by industrial emissions of NO_x has been studied in the past dacades. In this study, red mud coupling with phosphorus sludge were used to enhance the solution to absorb NO_x from the flue gas. Firstly, red mud reacted with the binder silicic acid in the phosphorus sludge, destroying the emulsion structure of the phosphorus sludge. Then, the P₄ in the phosphorus sludge is completely released, and the P₄ reacted with O₂ in the flue gas to produce O₃ and O. NO and NO₂ contained in the flue gas reacted with the active O and O₃ to produce high-valent NO_x, such as NO₃, N₂O₅. At last, the mixed slurry of red mud and phosphorus sludge absorbed the high-valent NO_x, resulting in the formation of Ca₅(PO₄)₃F along with HNO₃. Using phosphorus sludge to produce O₃ in the reaction process can reduce the production cost of O₃ and achieve waste utilization. Meanwhile, the interaction between red mud and phosphorus sludge can promote phosphorus sludge to produce O₃ and remove F^- from phosphorus sludge, as well as avoid the problem of secondary pollution. This study should be helpful for red mud and phosphorus sludge utilization and flue gas denitration.