Effect of Aluminum Sulfate and Succinic Acid on the Growth Law of α-Calcium Sulfate Hemihydrate under Microwave Irradiation

Abstract

The existing α-hemihydrate gypsum preparation process has low production efficiency and high energy consumption. In this paper, α-type hemihydrate gypsum was prepared by microwave irradiation using phosphogypsum as the raw material, calcium chloride solution as the reaction medium, and succinic acid and aluminum sulfate as crystal-transforming agents. Both aluminum sulfate and succinic acid were studied to determine the mechanism influencing the effect on the growth of α-type hemihydrate gypsum crystals. This study found that, without added succinic acid or aluminum ions, the crystal transformation rate of α-calcium sulfate hemihydrate reached 96% with the average length-diameter ratio reaching 21 after 1 h; when the dosage of succinic acid was 0.02%, the crystal transformation rate of α-calcium sulfate hemihydrate reached 96% with the average length-diameter ratio reaching 1.5 after 1.5 h; and when the aluminum ion dosage was 5 mM, the crystal transformation rate of α-calcium sulfate hemihydrate reached 97% with the average length-diameter ratio reaching 12.3 after 1 h. In addition, it was discovered that the reaction time was significantly shortened under microwave irradiation, and with an increase in succinic acid content, the regulation of the microscopic morphology of the calcium sulfate hemihydrate crystals was continuously enhanced and the aspect ratio of the crystals was continuously reduced. The EDS and Fourier transform infrared spectroscopy (FTIR) analysis showed that succinic acid did not adsorb onto the hemihydrate gypsum crystal during the reaction under microwave irradiation. The X-ray photoelectron spectroscopy (XPS) analysis revealed that aluminum ions affected crystal growth by incorporating into calcium sulfate hemihydrate crystals after reacting with sulfate radicals.