Sulfur trioxide Flue Gas Desulfurization processes(FGD) remove ulfur dioxidey its irreversible reactive absorption with lime or limestone,or by its reversible absorption in sodium citrate solutiouns.There are many electeochemical methods that have been studied for this purpose.Most of these involve the direct oxidation of sulfur dioxde to sulfate ion,although some involve its reduction to elemental sulfur.