Rapid synthesis of alpha calcium sulfate hemihydrate whiskers in glycerol-water solution by using flue-gas-desulfurization gypsum solid waste

The feasibility of fabricating alpha calcium sulfate hemihydrate (α-CSH) whiskers by using flue-gas-desulfurization (FGD) gypsum as source materials was studied. Crystal phase- and morphology-controlled crystallization of gypsum were realized in the designed glycerol-water reaction system. l-glutamic acid was found to accelerate the conversion of calcium sulfate dihydrate (CSD) into α-CSH whiskers by intercalating into layered CSD structure. The time-dependent experiments indicate rod-like CSD first splits into layered structure and then fascicular structure and finally single crystals. The splitting crystallization owing to lattice expansion of CSD generates α-CSH whiskers with a high aspect ratio (∼1:200). The facile method to convert FGD gypsum solid waste into CSD and finally α-CSH whiskers may prove particularly useful in the design of recyclable FGD gypsum with significant environmental impact, and it is particularly important in environmental remediation and green economics.