Synthesis of α-CaSO4·0.5H2O from flue gas desulfurization gypsum regulated by C4H4O4Na2·6H2O and NaCl in glycerol-water solution

A brand new method to transform flue gas desulfurization gypsum (FGD gypsum) into α-calcium sulfate hemihydrate (α-HH) with short hexagonal prisms mediated by succinic acid disodium salt hexahydrate (C 4 H 4 O 4 Na 2 ·6H 2 O) and NaCl in glycerol-water solution is studied, in which the appropriate reaction temperature is 90 °C. The addition of NaCl facilitates the dissolution of calcium sulfate dihydrate (DH) and creates much higher supersaturation which is a greater driving force for the phase transformation from DH to α-HH. C 4 H 4 O 4 Na 2 ·6H 2 O as the crystal modifier effectively suppresses the α-HH crystal growth along the c axis, and the products generally change from needle-like particles to fat and short hexagonal prisms, which is attributed to the preferential adsorption of C 4 H 4 O 4 2− on the top facets of the crystals by chelating Ca 2+ . A brand new method to prepare α-CaSO 4 ·0.5H 2 O with low aspect ratios from flue gas desulfurization gypsum in glycerol-water solution was presented, in which NaCl was used as the phase transition accelerator and C 4 H 4 O 4 Na 2 ·6H 2 O as the crystal modifier.