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  • Title: [Inhibition of sulfite oxidation catalyzed by heavy metals in dual alkali flue gas desulfurization slurry].
    Author: Yu J, Guan BH, Liu WX, Hu DQ, Wu ZB.
    Journal: Huan Jing Ke Xue; 2010 Mar; 31(3):591-7. PubMed ID: 20358813.
    Abstract:
    Heavy metals accumulated in slurry of dual alkali flue gas desulfurization (FGD) present a significant catalysis to SO3(2-) oxidation, resulting in a waste of effective components for desulfurization. Na2S was adopted to precipitate heavy metal ions in FGD slurry, and the oxidation rate of SO3(2-) was obtained under different concentrations of heavy metal ions, to reveal the inhibition effect of Na2S on SO3(2-) oxidation catalyzed by heavy metal ions. Mn2+ showed a remarkable catalysis to SO3(-2) oxidation, as the initial oxidation rate of SO3(2-) was tripled to 0.65 mmol/(L x min) by adding 1.0 mmol/L Mn2+ into the slurry. SO3(2-) was catalytically oxidized rapidly with the reaction order 0.169 of Mn2+ within first 60 minutes, so it is of great importance to control the concentration of Mn2+ to inhibit SO3(2-) oxidation. At initial pH value of 6.50-8.50, Na2S removed heavy metal ions effectively from FGD slurry. Higher pH value favored the removal of heavy metal ions. The removal efficiencies of Mn2+, Zn2+, Ni2+ and Cd2+ were 91.0%, 88.1%, 85.5%, and above 99.9% respectively under the conditions of initial pH value 8.50 and Na2S dosage 240.0 mg/L. Mn2+ could be used as an indicator for the concentration of the heavy metal ions in the slurry. As the Mn2+ concentration decreased from 1.0 mmol/L to 5.0 x 10(-3) mmol/L by adding Na2S, the initial oxidation rate of SO3(2-) decreased by 64.6% to 0.23 mmol/(L x min). The desulfurization efficiencies increase 3.8%-5.1% by adding Na2S in a pilot scale setup. It comes to conclusion that heavy metal ions precipitation by adding Na2S with an indicator of Mn2+ to inhibit catalytic oxidation of SO3(2-) is feasible to reduce the consumption of desulfurizer in FGD slurry.
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