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Thermal decomposition of syngenite, K2Ca(SO4)2·H2O |
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| Authors: | JTheo Kloprogge Zhe Ding Roelof D Schuiling Ray L Frost |
| Institution: | a Inorganic Materials Research Program, School of Physical and Chemical Sciences, Queensland University of Technology, 2 George Street, G.P.O. Box 2434, Brisbane, Qld 4001, Australia b Department of Geochemistry, Institute of Earth Sciences, Utrecht University, P.O. Box 80021, 3508 TA Utrecht, The Netherlands c Analytical Electron Microscopy Facility, Faculty of Science, Queensland University of Technology, 2 George Street, G.P.O. Box 2434, Brisbane, Qld 4001, Australia |
| Abstract: | The thermal decomposition of syngenite, K2Ca(SO4)2·H2O, formed during the treatment of liquid manure has been studied by thermal gravimetric analysis, differential scanning calorimetry, high temperature X-ray diffraction (XRD) and infrared emission spectroscopy (IES). Gypsum was found as a minor impurity resulting in a minor weight loss due to dehydration around 100 °C. The main endothermic dehydration and decomposition stage of syngenite to crystalline K2Ca2(SO4)3 and amorphous K2SO4 is observed around 200 °C. The reaction involves a solid-state re-crystallisation, while water and the K2SO4 diffuse out of the existing lattice. The additional weight loss steps around 250 and 350 °C are probably due to presence of larger syngenite particles, which exhibit slower decomposition due to the slower diffusion of water and K2SO4 out of the crystal lattice. A minor endothermic sulphate loss around 450 °C is not due to the decomposition of syngenite or its products or of the gypsum impurity. The origin of this sulphate is not clear. |
| Keywords: | Differential scanning calorimetry Infrared emission spectroscopy Sulphate double salt Syngenite Thermogravimetry-mass spectroscopy |
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