The crystal transformation characteristics from dihydrate gypsum to α-hemihydrate gypsum in Mg(NO3)2 solution

doi:10.1016/j.cjche.2025.07.009

Abstract

Abstract: The preparation of high-strength α-hemihydrate gypsum (α-HH) from dihydrate gypsum (DH) is a potential way to improve the utilization rate of industrial gypsum. α-HH with a low aspect ratio was prepared by atmospheric salt solution method, using Mg(NO₃)₂ solution as the salt medium. The effects of reaction temperature, reaction time, Mg(NO₃)₂ concentration, pH value, and the solid-to-liquid ratio on the purity, yield and aspect ratio of the product were investigated systematically. Under the optimal reaction conditions of 95 ℃, 4 h, 40% (mass) Mg(NO₃)₂, pH 5, and a solid-liquid ratio of 1:5, the yield and purity of the product could reach 89.67% and 99.85%, respectively. Additionally, the average aspect ratio of this product was 2.02, and the compressive strength reached 58.2 MPa. The regulation mechanism was studied by calculating the adsorption energies of Mg(NO₃)₂ on different crystal planes of α-HH, which indicated that Mg(NO₃)₂ exhibited the strongest adsorption on the (1 1 1) plane, and this preferential adsorption retarded the axial growth of α-HH, resulting in a reduced aspect ratio of the crystals. These findings suggest that the Mg(NO₃)₂ solution is an effective approach for preparing high-strength α-HH with controlled morphology.

Key words: α-Hemihydrate gypsum, Mg(NO₃)₂, Crystal morphology, Crystal regulation mechanism

摘要： The preparation of high-strength α-hemihydrate gypsum (α-HH) from dihydrate gypsum (DH) is a potential way to improve the utilization rate of industrial gypsum. α-HH with a low aspect ratio was prepared by atmospheric salt solution method, using Mg(NO₃)₂ solution as the salt medium. The effects of reaction temperature, reaction time, Mg(NO₃)₂ concentration, pH value, and the solid-to-liquid ratio on the purity, yield and aspect ratio of the product were investigated systematically. Under the optimal reaction conditions of 95 ℃, 4 h, 40% (mass) Mg(NO₃)₂, pH 5, and a solid-liquid ratio of 1:5, the yield and purity of the product could reach 89.67% and 99.85%, respectively. Additionally, the average aspect ratio of this product was 2.02, and the compressive strength reached 58.2 MPa. The regulation mechanism was studied by calculating the adsorption energies of Mg(NO₃)₂ on different crystal planes of α-HH, which indicated that Mg(NO₃)₂ exhibited the strongest adsorption on the (1 1 1) plane, and this preferential adsorption retarded the axial growth of α-HH, resulting in a reduced aspect ratio of the crystals. These findings suggest that the Mg(NO₃)₂ solution is an effective approach for preparing high-strength α-HH with controlled morphology.

关键词: α-Hemihydrate gypsum, Mg(NO₃)₂, Crystal morphology, Crystal regulation mechanism

Yunfei Li, Xinyue Deng, Shiqin Yin, Li Lv, Shengwei Tang, Tao Zhang. The crystal transformation characteristics from dihydrate gypsum to α-hemihydrate gypsum in Mg(NO₃)₂ solution[J]. Chinese Journal of Chemical Engineering, 2025, 88(12): 274-283.

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The crystal transformation characteristics from dihydrate gypsum to α-hemihydrate gypsum in Mg(NO₃)₂ solution

The crystal transformation characteristics from dihydrate gypsum to α-hemihydrate gypsum in Mg(NO₃)₂ solution

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