Simultaneous removal of SO2 and NO using a novel method with red mud as absorbent combined with O3 oxidation

Aiming at SO2 and NOx in industrial flue gas, the simultaneous removal of SO2 and NOx was conducted using red mud as absorbent with O3 oxidation. The effects of different factors on the desulfurization and denitration efficiency were investigated. The results show that the increase of oxidation temperature is not conducive to the absorption of NOx (O3/NO molar ratio >1). Low concentration of SO2 promotes the absorption of NOx, however high concentration of SO2 inhibits absorption of NOx. The main product after desulfurization and denitration of red mud solid residue is bassanite (CaSO4·0.5H2O). In addition, when the pH is greater than 5, calcium carbonate and sodium alkali play major roles in red mud, and when 3.5< pH < 5, sodium aluminosilicate hydrate (1.08Na2O·Al2O3·1.68SiO2·1.8H2O), calcium nepheline (Na6CaAl6Si6(CO3)O24·2H2O) and garnet (Ca3Al2(SiO4)(OH)8) take part in the reaction. According to typically practical conditions with oxidation temperature at 130 °C and the O3/NO molar ratio being 1.8, the desulfurization efficiency of red mud can reach 93 % in the first hour, and the denitration efficiency can be maintained at about 87 %. Besides, the reaction mechanism with multi oxidation absorption steps was also proposed.