| Summary: | 碩士 === 國立臺北科技大學 === 環境規劃與管理研究所 === 93 === A novel research was conducted for the chemical reaction between sulfur dioxide (SO2) and zero valent iron (ZVI), and to confirm the feasibility of SO2 removal based on ZVI strong reducing abilities. Four different parameters: temperature(573K, 623K, 673K, 723K and 773 K), influent concentration (380, 650, 900 and 1300 ppm), flowrate(115, 150, 200, 250 ml/min) and ZVI dosages (0.25 g, 0.5, 0.75 g and 1.0 g) were tested in two different types of reactors: packed and fluidized column studies.
For the controlled temperatures of 573 K-773 K, SO2 was completely removed for temperature of 623 K-773 K, but not for 573 K. Exhaustion test was conducted for the four working temperatures and the results indicated, when the temperature was higher, the run time (before breakthrough) was also longer. Since almost complete removal was achieved before breakthrough, SO2 reductions by ZVI (as mg SO2/g ZVI) was used to identify the efficiency of the SO2 for the different operating conditions. In these studies, higher temperature, and more ZVI dosage, can all achieve higher SO2 reduction (as mg SO2/g ZVI), while the SO2 reduction was decreasing with increasing influent concentration and inflow rate.
From fluidized column studies, the empty bed contact time (EBCT) did not show meaningful correlation to the SO2 removal efficiency, since the empty bed volume of ZVI was not linearly proportional to the flowrate as it was expected. The ZVI weight /flowrate (W/Q) or ZVI surface area /flowrate(S/Q), instead of EBCT, is linearly proportional to the SO2 removal efficiency.
XRD (X-Ray Diffraction) was conducted to analyze the crystal structure and oxidation state of the reacted ZVI. Several species were determined from the spectrum: Feo(ZVI) and FeS, Fe3O4 and Fe2O3. ZVI was the most prevalent species: FeS, Fe3O4 and Fe2O3 were less. Apparently, the double bondings between sulfur and oxygen were broken first then the ZVI reacted with sulfur and oxygen, respectively. Therefore, two reactions are proposed based on the XRD analytical results:
5Fe+2SO2=2FeS+Fe3O4 (Equation 1)
7Fe+3SO2=3FeS+2Fe3O4 (Equation 2)
SO2 reductions by ZVI (mg SO2/g ZVI) for various operating conditions were varied from 2.9~75.6 and 3.2~45.9 mg SO2/g ZVI with respect to packed column and fluidized column respectively. Stoichiometrically compared to either Equation 1 or Equation 2, there was only less than 16.5 % ZVI consumed regarding theoretical ZVI usage. Thus, it can be concluded that the heterogeneous reaction was only occurred on the ZVI surface instead of bulk of the ZVI.These ZVI can be reused after regeneration since more than 84% of the ZVI were actually intact.
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