Miscibility in the CaSO4·2H2O–CaSeO4·2H2O system: Implications for the crystallisation and dehydration behaviour |
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| Institution: | 1. Department of Chemistry, Graduate School of Science and Engineering, Tokyo Metropolitan University, Minami-Osawa 1-1, Hachi-Oji, Tokyo, 192-0397, Japan;2. Institute of Chemistry, Eötvös Loránd University, P.O. Box 32, 1512 Budapest, Hungary;3. Laboratory of Nuclear Chemistry, Chemical Research Center, Hungarian Academy of Sciences, 1512 Budapest, P.O. Box 32, Hungary;4. Department of Biological and Environmental Chemistry, Faculty of Humanity-Oriented Science and Engineering, Kinki University, 11-6 Kayanomori, Iizuka, Fukuoka 820-8555, Japan |
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| Abstract: | SeO42? ions can substitute for sulphate in the gypsum structure. In this work crystals of different Ca(SO4,SeO4)·2H2O solid solutions were precipitated by mixing a CaCl2 solution with solutions containing different ratios of Na2SO4 and Na2SeO4. The compositions of the precipitates were analysed by EDS and the cell parameters were determined by X-ray powder diffraction. Moreover, a comparative study on dehydration behaviour of selenate rich and sulfate rich Ca(SO4,SeO4)·2H2O solid solutions was carried out by thermogravimetry.The experimental results show that the Ca(SO4,SeO4)·2H2O solid solution presents a symmetric miscibility gap for compositions ranging from XCaSO4·2H2O = 0.23 to XCaSO4·2H2O = 0.77. By considering a regular solution model a Guggenheim parameter a0 = 2.238 was calculated. The solid phase activity coefficients obtained with this parameter were used to calculate a Lippmann diagram for the system Ca(SO4,SeO4)·2H2O–H2O. |
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