Thermal decomposition behavior of MnO₂/Mg-Al layered double hydroxide after removal and recovery of acid gas

Acidic gases such as HCl, SO₂, and NO_x are compounds that are generated through the incineration of waste products. Hence, an efficient method of removing such gases is highly desired. In this study, we present a novel method for treatment of acidic gases by using an MnO₂/Mg-Al layered double hydroxide (MnO₂/Mg-Al LDH), which provides several advantages in removing NO when compared to other removal methods, in addition to enabling the removal of HCl and SO₂. We tested the recovery of acidic gases using the dry process, which separates the adsorbed gases from the LDH and recovers them as gases again, allowing them to be reused, and the adsorbent to be regenerated. To achieve this, we analyzed the pyrolysis behavior of MnO₂/Mg-Al LDH at different temperatures and with various acidic gases adsorbed, using thermogravimetry (TG) and evolved gas analysis-mass spectrometry (EGA-MS), and further studied the recovery of adsorbed acidic gases. For HCl, NO, and SO₂, outlet concentrations of 4000, 1000, and 950 ppm, respectively, were achieved, with recovery rates above 99% for all three. Additionally, we identified that for removal of both HCl and NO, MnO₂/Mg-Al LDH desorbed the acid gas and generated Mg-Al layered double oxide (Mg-Al LDO) as the LDH structure collapsed. Furthermore, for SO₂ removal, MgAl₂O₄ and MgO were generated. Overall, we confirmed that acidic gases such as HCl, NO, and SO₂, can be recovered with high efficiency and at a high concentration by using MnO₂/Mg-Al LDH. This method of removal can have many potential applications.