|Keywords||waste gypsum, reductive decomposition, calcium ferrite|
|Abstract||Most of waste gypsum boards have been landfilled in many countries, leading to a shortage of dump yards. In consideration of a sustainable and environment-friendly society based on recycling and utilization of Ca-based wastes, it is preferable to utilize waste gypsum as a substitute for lime, which is used in many industrial applications. In view of this, we propose to utilize waste gypsum as a substitute for lime, which is used as a sintering agent in ironwork process. Thus, the experiments were carried out to clarify the reductive decomposition behavior of CaSO4 in the absence or presence of 5 wt.% Fe2O3, SiO2 or Al2O3 under CO-CO2 atmosphere. The reductive decomposition of CaSO4 with or without the additives (Fe2O3, SiO2, or Al2O3) was carried out by means of thermogravimetric analyzer (TGA) and a gas-flow type tubular reactor under CO: 2vol%- CO2: 30vol%- N2: balance atmospheres in a temperature range of 573K-1573K (heating rate: 10K/min). From TGA results, when 5 wt.% Fe2O3 was added to CaSO4, it was found that the rate of reductive decomposition at temperatures above 1023 K was enhanced relative to single component (CaSO4 only) system. Moreover, the 1023 K temperature for the onset of the decomposition was lower than that of single component system. By comparison between CaSO4 single component system and CaSO4-SiO2 and CaSO4-Al2O3 systems, reductive decomposition was enhanced at temperatures above 1373 K. Meanwhile, reductive decomposition of CaSO4 in the absence or presence of additives was also performed on a gas-flow type tubular reactor at 1573K. In single component system, there existed a long induction period on the one hand whilst on the other hand, the induction period was shortened by the addition of additives. Similar to results from TGA, it was found that the rate of reductive decomposition of CaSO4 was enhanced by the addition of Fe2O3, SiO2 or Al2O3. In addition and in comparison to CaSO4 single component system, the amount of desulfurized CaSO4 was depressed during the reductive decomposition of CaSO4-additive samples. Finally, during the reductive decomposition, some calcium compounds such as Ca2Fe2O5, CaSiO3 and SiS2, and CaAl2O4 and Ca4Al6O12SO4 (Yeelimite) were detected in the reaction products in CaSO4 -Fe2O3, CaSO4-SiO2 and CaSO4-Al2O3 systems, respectively|
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|Name||Affiliation||Home page||Total pubs|
|Matsuda H||Department of Energy Engineering and Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603 Japan||15|
|Mihara N||Department of Energy Engineering and Science, Nagoya University, Furo-cho, Chikusa-ku, 464-8603, Japan||n-mihara@ees||4|
|Onyango MS||Department of Chemical and Metallurgical Engineering, Tshwane University of Technology, Arcadia Campus, Pretoria 0001, South Africa||3|
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