Calcium bisulfite oxidation in the flue gas desulfurization process catalyzed by iron and manganese ions

Among different flue gas desulfurization processes for control of sulfur dioxide emissions from combustion of fossil fuels, wet limestone scrubbing is the most widely used. Forced oxidation in the scrubber loop substantially improves the dewatering properties of the sludge, leading to the formation of gypsum (CaSO4.2H(2)O). In view of this, the present paper reports the experimental study of calcium bisulfite oxidation in the presence of catalysts (ferrous and manganese ions) both separately and simultaneously added in the reaction vessel. A laboratory-scale apparatus was used; the experiments were performed at a fixed oxygen partial pressure (21.3 kPa) and at a temperature of 45 degreesC. In particular, the effect of the simultaneous addition of both catalysts has been studied. The analysis of the experimental results, carried out by using the theory of mass transfer with chemical reaction, indicated that the slow reaction regime has been explored and the transition from the kinetic to the diffusional subregime identified. Experimental results, as compared with those obtained in the presence of the single catalytic species (Mn2+ alone and Fe2+ alone) allowed one to observe the synergistic effect that the two catalysts added simultaneously have on the oxidation reaction.