For recovering CaO from spent gypsum at relatively low temperatures, decomposition behavior of CaSO
4 was studied by using a thermogravimetric analyzer in CO-CO
2-N
2 and H
2-C
2-N
2 atmosphere in a temperature range of 1123-1273K. The conversions of CaSO
4 to CaO and CaS byproduct were determined by the weight change of the decomposition of CaSO
4 and the oxidation of CaS to CaSO
4, respectively.
It was found that the conversion of CaSO
4 to CaO increased with an increase in temperature in both CO-N
2 and H
2-N
2 atmosphere. On the other hand, the formation of CaS byproduct increased with the increase in CO and H
2 concentrations, whereas the yield of CaO was decreased. It was possible to suppress the formation of CaS by adding high concentration CO
2 to CO-O
2-N
2 and H
2-CO
2-N
2 gas atmosphere. The conversion, greater than 90% of CaSO
4 to CaO was obtained in a mixed gas of CO : 2%, CO
2 : 30%, N
2 : 68% at 1273K. The formation of CaS byproduct was not detectable in this condition.
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