Effect of Copper Chloride on Phase Structure and Properties of Synthesized Materials from Flue Gas Desulfurization Gypsum

This research investigates the influence of crystal modifying agent, copper chloride (CuCl2) (0.3, 0.45, and 0.6 g), on the phase structure and characteristics of materials derived from flue gas desulfurization (FGD) gypsum. The raw material underwent hydrothermal transformation with 0.01 M H2SO4 at 90°C for 1 hour. XRD analysis revealed a notable shift in phase structure from hexagonal calcium sulfate dihydrate (DH) in FGD gypsum to monoclinic calcium sulfate hemihydrate (alpha-HH) up to 91%in the synthesized products, with an increasing CuCl2 content. SEM analysis revealed the elongated whisker-shaped particles (110.70 µm to 207.90 µm) of alpha-HH with higher CuCl2 concentrations. Specifically, when incorporating 0.6 g of CuCl2 in 0.01 M H2SO4 at 90°C, the longest alpha-HH crystals resulted in the cast plaster with the highest flexural strength of approximately 4.92 MPa, demonstrating suitability for applications requiring sufficient mechanical strength. Thermal analysis confirmed the complete conversion of the solid phase to alpha-HH at 1200°C. Additionally, the study revealed that higher CuCl2 content led to shorter setting time. These results suggest potential applications of the present synthesized materials from FGD gypsum in industries such as ceramics casting and dental materials, where precise control over material properties is critical.