Oxidation of FGD-CaSO3 and effect on soil chemical properties when applied to the soil surface

Use of high-sulfur coal for power generation in the United States requires the removal of sulfur dioxide (SO2) produced during burning in order to meet clean air regulations. If SO2 is removed from the flue gas using a wet scrubber without forced air oxidation, much of the S product created will be sulfite (SO32-). Plants take up S in the form of sulfate (SO42-). Sulfite may cause damage to plant roots, especially in acid soils. For agricultural uses, it is thought that SO32- in flue gas desulfurization (FGD) products must first oxidize to SO42- in soils before crops are planted. However, there is little information about the oxidation of SO32- in FGD product to SO42- under field conditions. An FGD-CaSO3 was applied at rates of 0, 1.12, and 3.36 Mg ha−1 to the surface of an agricultural soil (Wooster silt loam, Oxyaquic Fragiudalf). The SO42- in the surface soil (0–10 cm) was analyzed on days 3, 7, 17, 45, and 61. The distribution of SO42- and Ca in the 0–90 cm soil layer was also determined on day 61. Results indicated that SO32- in the FGD-CaSO3 rapidly oxidized to SO42- on the field surface during the first week and much of the SO42- and Ca moved downward into the 0–50 cm soil layer during the experimental period of two months. It is safe to grow plants in soil treated with FGD-CaSO3 if the application is made at least three days to several weeks before planting.