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Sensors 2009, 9(7), 5059-5067; doi:10.3390/s90705059

Identification of Calcium Sulphoaluminate Formation between Alunite and Limestone

1
Mineral Resources Research Division, Korea Institute of Geoscience & Mineral Resources, 30 Gajeong-dong, Yuseong-gu, Daejeon 305-350, Korea
2
Department of Energy Resources Engineering, Seoul National University, 599 Gwanak-ro, Gwanak-gu, Seoul 151-742, Korea
*
Author to whom correspondence should be addressed.
Received: 31 May 2009 / Revised: 10 June 2009 / Accepted: 10 June 2009 / Published: 25 June 2009
(This article belongs to the Section Chemical Sensors)
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Abstract

This study was carried out to identify the conditions of formation of calcium sulphoaluminate (3CaO·3Al2O3·CaSO4) by the sintering of a limestone (CaCO3) and alunite [K2SO4·Al2(SO4)3·4Al(OH)3] mixture with the following reagents: K2SO4, CaCO3, Al(OH)3, CaSO4·2H2O, and SiO2. When K2SO4, CaCO3, Al(OH)3, CaSO4·2H2O were mixed in molar ratios of 1:3:6:3 and sintered at 1,200~1,300 °C, only 3CaO·3Al2O3·CaSO4 and calcium langbeinite (2CaSO4·K2SO4) were generated. With an amount of CaO that is less than the stoichiometric molar ratio, 3CaO·3Al2O3·CaSO4 was formed and anhydrite (CaSO4) did not react and remained behind. With the amount of CaSO4 that is less than the stoichiometric molar ratio, the amounts of 3CaO·3Al2O3·CaSO4 and 2CaSO4·K2SO4 decreased, and that of CaO·Al2O3 increased. In the K2SO4-CaO-Al2O3-CaSO4-SiO2 system, to stabilize the formation of 3CaO·3Al2O3·CaSO4, 2CaSO4·K2SO4, and β-2CaO·SiO2, the molar ratios of CaO: Al2O3: CaSO4 must be kept at 3:3:1 and that of CaO/SiO2, over 2.0; otherwise, the generated amount of 3CaO·3Al2O3·CaSO4 decreased and that of gehlenite (2CaO·Al2O3·SiO2) with no hydration increased quantitatively. Therefore, if all SO3(g) generated by the thermal decomposition of alunite reacts with CaCO3 (or CaO, the thermal decomposition product of limestone) to form CaSO4 in an alunite- limestone system, 1 mol of pure alunite reacts with 6 mol of limestone to form 1 mol of 3CaO·3Al2O3·CaSO4 and 1 mol of 2CaSO4·K2SO4. View Full-Text
Keywords: alunite; limestone; calcium sulphoaluminate; calcium langbeinite alunite; limestone; calcium sulphoaluminate; calcium langbeinite
This is an open access article distributed under the Creative Commons Attribution License (CC BY 3.0).

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MDPI and ACS Style

Kim, H.-S.; Han, G.-C.; Ahn, J.-W.; Cho, K.-H.; Cho, H.-C. Identification of Calcium Sulphoaluminate Formation between Alunite and Limestone. Sensors 2009, 9, 5059-5067.

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