Buffer effect of MgO on Na2SO3 to stabilize S(IV) for the enhancement in simultaneous absorption of NOx and SO2 from non-ferrous smelting gas

Abstract

Oxidation-reduction-absorption based on sulfite is a promising process for simultaneous removal of NO_x and SO₂. However, excessive oxidation of sulfite and competitive absorption between NO_x and SO₂ limit its application. A matching strategy between antioxidants and alkaline agents has been proposed to solve these problems and enhance the absorption process. The comparison results of inhibitors showed that hydroquinone exhibited long-term high-efficiency inhibition of S(IV) (SO₃^2-/HSO₃^-) oxidation. The comparison of alkaline agents showed that the Na₂SO₃ solution with heterogeneous mixture of MgO and hydroquinone exhibited better absorption performance than that with other combinations. The absorption amounts of NO_x in 0.15 mol/L Na₂SO₃ 50 mL solution added 0.1% hydroquinone (HQ) with 0.09 mol/L MgO were 2.24 mmol, which improved 5 times than that without additives. In addition, studies on the influence of pH showed that the pH of MgO mixture could be stabilized at 9-10 for a long time, while the pH of Na₂CO₃ mixture decreased faster. Further studies suggested that the hydration of MgO resulted in the solution with MgO keeping high pH. This is also the main reason why the combination of MgO and hydroquinone is superior to the combination of Na₂CO₃ and hydroquinone in desulfurization and denitration performance.

Keywords: Heterogeneous mixture; Match effect; Non-ferrous metal smelting flue gas; Oxidation inhibition; Oxidation–reduction-absorption.