Autoclave-Free Formation of α-Hemihydrate Gypsum

Flue gas gypsum may be converted to α-hemihydrate by suspending the starting material in inorganic salt solutions of high concentration or in diluted sulfuric acid and maintaining the suspension at boiling, or near boiling temperature for a period of time. The crystal morphology of the produced α-hemihydrate gypsum and, thus, its quality depend significantly on the composition of the liquid phase. Additions of different carbonic acids may improve the quality of the product distinctly. Under optimal working conditions the quality of the formed α-hemihydrate gypsum is similar to that of a material produced in an autoclave.