The controllable transformation of flue gas desulfurization(FGD)gypsum to calcium sulfate hemihydrate(HH)whiskers under facile,readily monitored,and cost-effective hydrothermal conditions could play a vital role in the preparation of high quality HH whiskers and improve our understanding of the trans-formation process.This work assessed the conversion of FGD gypsum to HH whiskers in 5×10-4 mol/L H2SO4 and 1.5 wt％CuCl2 at 120 ℃ while determining the effects of temperature as well as H2SO4 and CuCl2 concentrations on transformation kinetics.The preparation of HH whiskers was found to involve a solution-mediated transformation from the dihydrate(DH)to the α-HH.This transition was determined to proceed via a dissolution crystallization mechanism,the rate of which was controlled by nucleation and growth of the HH whiskers.An autocatalytic kinetic model was established based on variations in the HH whiskers mole fraction over time,and this model accurately fit the experimental data with R2 =0.990.Increasing the temperature or H2SO4 concentration accelerated the transformation by modifying the super-saturation and water activity in the reaction solution,while increasing the CuCl2 concentration had the opposite effect.The hydrothermal conditions had an important effect on the transformation from FGD gypsum to HH whiskers.