Effect of Al2(SO4)3 Additive on the Properties of Calcined Gypsum Prepared from Flue Gas Desulfurization

Abstract

In order to upgrade the utilization of flue gas desulfurization (FGD) gypsum, crystal modifier aluminum sulfate (Al₂(SO₄)₃) was added into FGD gypsum to prepare calcined gypsum by calcining at normal pressure, and the effect of Al₂(SO₄)₃ addition on the performance of calcined gypsum was studied. The results show that the addition of Al₂(SO₄)₃ to FGD gypsum is slightly beneficial to promote the crystallization of hemihydrate gypsum (HH) along the a-axis direction. The Al₂(SO₄)₃ addition also has a quick-setting effect on gypsum plaster during the hydration process, meanwhile inhibiting the growth of the (020) crystal plane of dihydrate gypsum (DH), then promoting uniform growth and aggregation along the c-axis. The close stacking makes hardened gypsum body dense and improves the strength of calcined gypsum. The strength of calcined gypsum prepared by calcining FGD gypsum with Al₂(SO₄)₃ of 0.6 wt.% at 170 ℃ for 2 h is the highest. 2 h and 7 d flexural strength are 3.80 MPa and 7.20 MPa, and 2 h and 7 d compressive strength are 9.05 MPa and 19.23 MPa, respectively. In addition, 2 h flexural and compressive strength of the calcined gypsum with 0.6 ~ 1.0 wt.% of Al₂(SO₄)₃ prepared at 170 ~ 180 ℃ for 2 h increase by 16 ~ 22 % and 20 ~ 33 %, respectively, which is very advantageous for the high value-added reuse of FGD gypsum for the preparation of high-quality calcined gypsum.