Calcination of calcium sulphoaluminate cement using flue gas desulfurization gypsum as whole calcium oxide source

Flue gas desulfurization (FGD) gypsum is an industrial by-product of the desulfurization process. The gross product of FGD gypsum has reached 550 million tons in China by 2016 and quite a portion was discarded. The purpose of this study is to investigate the feasibility of an innovative concept of producing the CSA cement based on sulfur recovery and entirely made of the FGD gypsum to replace natural gypsum and limestone as CaO and SO3 sources. A mixture of industrial solid waste was calcined under different calcination conditions to study the decomposition behavior of FGD gypsum and properties of CSA cement made from the FGD gypsum. Experimental results show that it is feasible to use the FGD gypsum to entirely supply the CaO and SO3 of this cement, the optimized calcination temperature is between 1270 and 1310 degrees C, and the suitable retention time is 60-100 min. The highest compressive strengths of 63.3, 85.3, 102.8 MPa were attained at 1, 3, and 28 d, respectively when the temperature was kept at 1310 degrees C for 60 min. Results also indicate that the FGD gypsum decomposition, which is mainly influenced by calcination temperature, retention time and alumina-silica ratio, has a significant impact on the clinker mineral phase formation. The novel technical idea developed in this research can greatly improve the utilization of FGD gypsum and may reduce about 50% of CO2 emission in routine production. (C) 2019 Elsevier Ltd. All rights reserved.