Preparation of high-performance building gypsum by calcining FGD gypsum adding CaO as crystal modifier

Preparation of building gypsum from flue gas desulfurization (FGD) gypsum is of great value in effectively utilizing the FGD gypsum. An economical and effective process for preparing high-performance building gypsum from the FGD gypsum was proposed. CaO, as a crystal modifier, was added to adjust the quality of hemihydrate gypsum converted in the dehydration process of FGD gypsum. The effects of CaO addition, calcining temperature and holding time on the properties of building gypsum were investigated. The results show that the obtained hemihydrate gypsum mixing with water can prepare high-performance building gypsum after the FGD gypsum adding 3–5 wt% of CaO is calcined at 160–220 °C for 1.5–2 h. Considering the low-temperature calcination error and preparation cost, 3 wt% CaO is added to the FGD gypsum and the mixture is calcined at 200 °C for 1.5 h. The initial and final setting time of building gypsum prepared by this process is 4.183 and 6.75 min, and 2 h and 3 d flexural/compressive strengths reach 2.8/6.2 and 3.5/10.6 MPa, respectively. This research can provide useful information for large-scale reuse of solid waste FGD gypsum in the future.