Effect of CuCl2 on hydrothermal crystallization of calcium sulfate whiskers prepared from FGD gypsum

Using purified flue-gas desulfurization (FGD) gypsum as raw material, effects of CuCl2 on crystal morphology, phase structure, aspect ratio and crystallization of hydrothermal products prepared via hydrothermal crystallization in H2SO4-H2O solutions were investigated. The results show that dosage of CuCl2 has a significant effect on the morphology, aspect ratio and crystallization of calcium sulfate whiskers (CSWs), but no effect on their phase transformation. At a dosage of 15 g CuCl2/kg FGD gypsum, the produced calcium sulfate whiskers had diameters ranging from 1 to 3 m with average aspect ratio greater than 200. Transmission electron diffraction patterns and highly magnified surface morphology of CSWs were found different from those of self-assembly crystals. Compared to self-assembly crystals, the produced CSWs showed a single crystal structure and their surface was very smooth.