Using FGD gypsum as the raw material, short columnar‐shaped α‐calcium sulfate hemihydrate can be prepared with succinic acid in hydrothermal autoclave method with a low salt content. The influence of washing times, slurry concentration, salt content, reaction temperature, pH and the amount of succinic acid were investigated. The research shows that: short columnar α‐calcium sulfate hemihydrate with the length of 50 μm and length‐diameter ratio of 1, dry compressive strength of which is similar to 40 grade was obtained at the slurry concentration of 14%, salt content of 3%, succinic acid of 0.07% after three times washing under 115°C without the change of pH value. After 5 times circulation of mother liquid, the morphology of the product had no significant difference with the initial product and recycling rate of sodium chloride was not less than 90%.
Large‐grained short columnar α‐calcium sulfate hemihydrate with the length of 50 μm and length‐diameter ratio of 1 can be prepared with a low salt content (3%) using FGD gypsum after three times washing. Analysis of low salt content and washing step was conducted in this paper. It shows that these two factors can make sure to get large‐grained crystals with smooth surface and high integrity and achieve the circulation of mother liquid further.