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

Aiming at SO₂ and NO_x in industrial flue gas, the simultaneous removal of SO₂ and NO_x 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 NO_x (O₃/NO molar ratio >1). Low concentration of SO₂ promotes the absorption of NO_x, however high concentration of SO₂ inhibits absorption of NO_x. 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.