α-Hemihydrate Gypsum from Flue Gas Desulphurization Gypsum

In this work, properties of sulphate technogenic raw material - flue gas desulphurization (FGD) gypsum have been investigated in order to obtain alpha-hemihydrate gypsum as gypsum binding material. FGD gypsum is produced as a by-product during the process of desulphurization of exhaust gas emitted in power stations heated by fuel containing sulphur. It has been determined that alpha-hemihydrate gypsum can be obtained from FGD gypsum under hydrothermal conditions at 125 degrees C and 130 degrees C. The compressive strength of gypsum samples is 13 MPa - 16 MPa after 2 h of hardening and it depends on temperature and time of isothermic curing. The compressive strength of the same samples in dry state is 49 MPa - 67 MPa. SEM analysis data showed that the properties of alpha-hemihydrate gypsum significantly depend on the shape and size of its crystals: when crystals have near form to regular hexagonal - shaped prism with length and width ratio approx. of 4 : 1, the gypsum exhibits the high quality mechanical and physical properties.