Uncatalyzed heterogeneous oxidation of calcium bisulfite

Wet limestone scrubbing is the most common flue gas desulfurization process for control ofsulfur dioxide emissions from combustion of fossil fuels. Forced oxidation in the scrubber loop improves thedewatering properties of the sludge, leading to the formation of gypsum (CaSO4.2H20). A literatureanalysis revealed that uncertainties on the mechanisms of the oxidation reaction and on the values of thekinetic parameters still remain. In the present work the oxidation rate was experimentally studied bycontacting pure oxygen or mixtures of oxygen and nitrogen with a calcium bisulflte solution. Theexperiments were carried out in a well-mixed bubbling reactor varying temperature, oxygen partial pressureand sulfite concentration, in the absence of solid calcium sulfite and of catalytic species. It was shown thatthe rate of the process is controlled by reaction kinetics, and that the reaction rate is zero order in dissolvedoxygen and 3/2-order in bisulfite ion.