Determination of Sulfite Content in Wet FGD Slurry by No‐Acid‐Additive Iodimetry: Experimental and DFT Studies

In this paper, experimental and density functional theory (DFT) studies on determining sulfite content in wet flue gas desulfurization (FGD) slurry by no-acid-additive iodimetry were carried out. Three different raw materials of slurry, filtrate, and filter residue were employed to react with iodine. The measurement accuracy of acid-additive iodimetry and no-acid-additive iodimetry was compared by conducting the reactions in an acidic open system (AOS) and non-acidic open system (NAOS). It was found that no-acid-additive iodimetry has a higher measurement accuracy compared to that of acid-additive iodimetry, even though acid-additive iodimetry could slightly accelerate the reactions. In no-acid-additive iodimetry, it was confirmed by DFT calculations that SO32-, HSO3-, and H2SO3 had different reaction mechanisms when reacting with iodine, and SO32- showed the lowest energy barrier of 5.78 kcal/mol. According to the relative abundance of SO32-, HSO3- and H2SO3, the dominant reaction pathway of sulfite reacting with iodine could be summarized as HSO3--> SO32-->+I2SO42- .