A readily monitored and controllable hydrothermal system for the facile, cost-effective transformation of FGD gypsum to calcium sulfate hemihydrate whiskers

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 transformation process. This work assessed the conversion of FGD gypsum to HH whiskers in 5 x10(-4) mol/L H2SO4 and 1.5 wt% CuCl2 at 120 degrees C 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 alpha-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 R-2 = 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. (C) 2020 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.

Automated summary

The controllable transformation of FGD gypsum to HH whiskers under hydrothermal conditions was studied, revealing a solution-mediated transformation process controlled by nucleation and growth. Increasing temperature or H2SO4 concentration accelerated the transformation, while increasing CuCl2 concentration had the opposite effect.