Activity Measurement for the FeCl 2 -ZnCl 2 System
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INTRODUCTION
THE dust and fly ash generated in the steelmaking industry and the municipal solid waste incineration process contain metallic elements such as Fe, Zn, Pb, and Cd with some amounts of halogens. These dusts have been treated mainly by pyrometallurgical processes due to the high contents of halogen elements.[1–4] In pyrometallurgical processes, zinc and lead, which exist as oxides in the dusts, are reduced or chlorinated by reaction with carbon and a chlorinating agent and are vaporized as metallic zinc or their chloride compounds, whereas iron is stable as oxides and residue in slag. The selective chlorination and evaporation behaviors of metallic elements in the process are important for the efficient recovery of zinc and lead from the dusts. Many studies have been carried out to investigate the chlorination and evaporation behaviors of the metallic elements in the dusts depending on oxygen and chlorine potentials.[5–13] The present authors[8,9] measured the vapor pressure of ZnCl2 between 823 and 873 K and that of PbCl2 between 923 and 1023 K with an Ar-O2 stream by the transpiration method to investigate the vaporization behaviors of ZnCl2 and PbCl2 under a highly oxidizing atmosphere. Matsuura and Tsukihashi[10,11] and Matsuura et al.[12,13] measured the chlorination and evaporation behaviors of the PbCl2-PbO system, ZnO, ZnFe2O4, and Fe2O3-ZnFe2O4-ZnO-PbO mixtures with Ar-Cl2-O2 gas by gravimetry to investigate the evaporation behaviors of zinc and lead in the dusts. In the recovery process of zinc and lead from the ironbased dust by chlorination and evaporation reactions, the evaporation behavior of iron, as well as those of zinc and lead, is important for reusing the recovered zinc and lead. Many results have been reported for the chlorination of iron oxides such as FeO, Fe3O4, and Fe2O3 with different chlorinating agents.[14–16] According to these SANG HAN SON, formerly Graduate Student, Department of Materials Engineering, The University of Tokyo, is Researcher with Ironmaking Research Group, Technical Research Labs., POSCO, Pohang 790-785, Korea. FUMITAKA TSUKIHASHI, Professor, is with the Department of Advanced Materials Science, Graduate School of Frontier Sciences, The University of Tokyo, Chiba 277-8561, Japan. Contact e-mail: [email protected] Manuscript submitted December 10, 2006. Article published online July 12, 2007. METALLURGICAL AND MATERIALS TRANSACTIONS B
results, the chlorinated iron oxides are evaporated as FeCl2, FeCl3, Fe2Cl6, and FeOCl gaseous species. TitiManyaka and Iwasaki[16] measured the chlorination behaviors of Fe and iron oxides with Cl2-O2 gas between 298 and 1073 K by thermogravimetry and reported that the oxygen potential upon the chlorination of iron oxides had a small effect in the range from 0 to 40 vol pct of the concentration of O2 in the Cl2 and O2 gas mixture. However, Matsuura et al.[12,13] showed that the chlorination and evaporation reactions of iron oxide from ZnFe2O4 and Fe2O3-ZnFe2O4-ZnO-PbO mixtures can be efficiently diminished by controlling the p
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