Recovery of CaO from CaSO₄ via CO reduction decomposition under different atmospheres

CaSO₄ reduction decomposition for CaO preparation provides a theoretical basis for the utilization of the industrial byproduct, gypsum. In this study, the effects of temperature (950 °C-1150 °C), CO₂/CO partial-pressure ratio (1-15), CO concentration (1%-5%), and O₂ concentration (1%-7%) on the preparation of CaO from CaSO₄ by CO reduction decomposition under different reaction atmospheres were investigated. The physical properties of CaO prepared by the decomposition of CaSO₄ and CaCO₃ were analyzed and compared. Finally, the reaction mechanism of the reduction decomposition of CaSO₄ to CaO by CO was studied. The findings reveal that CaSO₄ can be completely decomposed into CaO when the reaction temperature exceeds 1000 °C, CO% ≥ 2%, and P(CO₂)/P(CO) ≥ 8. Furthermore, the addition of an appropriate amount of O₂ can improve the yield of CaO in the products. In an O₂-CO-N₂ atmosphere, where O₂% = 7% and CO% = 16%, CaSO₄ can be completely decomposed into CaO without the addition of CO₂. The physical properties of CaO prepared by the reduction and decomposition of CaSO₄ are better than those prepared by the calcination of CaCO₃. An analysis of the reaction mechanism of the reduction decomposition of CaSO₄ by CO reveals that CaSO₄ generates CaO and CaS simultaneously. In addition, CaS can react with unreacted CaSO₄ to form CaO. Furthermore, it can react with CO₂ to produce CaO if an appropriate amount of CO₂ is added to the reaction atmosphere. The secondary interactions of CaS with CaSO₄ and CO₂ can significantly improve the yield of CaO in the product.