Abstract:

Phosphogypsum and desulfurization gypsum are industrial solid wastes with the largest storage capacity，and transforming them into hemihydrate gypsum as building materials is the best way for resource recycle.The α-hemihydrates gypsum was obtained by autoclave method from different industrial gypsum including desulfurized gypsum（FGD），phosphogypsum（PG） and natural gypsum（NG） as a control group.The effects of crystal modifiers including sodium dodecyl benzene sulfonate（SDBS），aluminum sulfate［Al₂（SO₄）₃］and compound crystal modifier（CM） on the morphology and strength of α-hemihydrates gypsum were investigated.The results showed that under autoclaved pressure at 135 ℃ for 5 h，α-hemihydrate gypsum could be prepared by three types of gypsum stably，three types of crystal modifiers had no impact on the phase composition of hemihydrate gypsum.0.4%CM could reduce the aspect ratio of crystals effectively.Based on T-test，the crystal modifiers had significant enhancing effect on the compression strength of α-hemihydrate gypsum prepared from FGD and NG，which was increased by more than 2 times to 13.59 MPa and 17.45 MPa，respectively.However，the strength of α-hemihydrates gypsum prepared by PG had no obvious change by adding crystal modifiers.The results exhibited that 0.4%CM could reduce the aspect ratio of crystals and improved compressive and flexural strength significantly of α-hemihydrates gypsum prepared from FGD and NG.The crystal modifier had no obvious impact on α-hemihydrates gypsum prepared from PG due to impurities.The results of the study provided a certain degree of theoretical guidance for the industrial production of different gypsum.

Key words: phosphogypsum, desulfurization gypsum, α-hemihydrates gypsum, crystal modifier, mechanical strength