Experimental study on preparation of α-hemihydrous gypsum by modification of desulfurized gypsum

In the process of preparing α-hemihydrous gypsum from desulfurized gypsum under atmospheric pressure, the optimum conditions of crystallization transformation and modification of desulfurized gypsum were studied. The effects of the type and concentration of composite salts (CaCl2, KCl, MgCl2 mixed solution) on the crystallization and modification of desulfurized gypsum were studied. The results were further verified by scanning electron microscopy (SEM) and differential scanning calorimetry (DSC/TGA), so as to determine the ideal directional crystallization control index. The experimental results show that temperature, type and concentration of salt solution are the most sensitive factors in the crystallization process of desulfurized gypsum. The optimal control conditions for obtaining α-hemihydrous gypsum with good crystalline form are temperature 95℃~98℃, concentration of composite salt solution (CaCl2: MgCl2: KCl = 25:5:1) is 25%~30%, and slurry concentration is greater than 20%.