Journal of Synthetic Crystals, Volume. 50, Issue 6, 1104(2021)
Regulation of Gypsum Crystalline and Morphology in Ca(H2PO4)2-H3PO4-K2SO4 System
In order to make the resource utilization of gypsum in the process of preparing KH2PO4 from Ca(H2PO4)2, the Ca(H2PO4)2 solution prepared by the reaction of H3PO4 and CaCO3 was mixed with K2SO4 solution. Then the regulation of gypsum crystalline and morphology in Ca(H2PO4)2-H3PO4-K2SO4 system was studied. The results show that the short columnar α-CaSO4·0.5H2O can be obtained from Ca(H2PO4)2-H3PO4-K2SO4 system by changing the reaction condition, including reaction time, reaction temperature, SO2-4 excess coefficient (ξ) and CaO content. The α-CaSO4·0.5H2O is formed at temperatures above 95 ℃ and CaO content of 3.0% to 5.0%(mass fraction, the same below), while CaSO4·2H2O is formed at low temperatures and CaO content of 5.5%. Meanwhile, with the increase of CaO content in the range of 3.0% to 5.0%, the aspect ratio of α-CaSO4·0.5H2O decreases. As the reaction time is longer than 20 min and the SO2-4 excess coefficient is greater than 1.4, K2SO4(CaSO4)5·H2O is easily formed, resulting in the increase of surface defects of gypsum crystals. Under the conditions of reaction time of 5 min, reaction temperature of 95 ℃, SO2-4 excess coefficient of 1.2 and CaO content of 5.0%, a short columnar α-CaSO4·0.5H2O crystals with length of 42 μm to 70 μm and diameter of 13 μm to 24 μm are prepared, the flexural strength and compressive strength of which are 5.61 MPa and 33.74 MPa, respectively. The yield of potassium and decalcification rate of the filtrate are 94.23% and 83.80%, respectively.
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WU Qin, YANG Lin, YI Yun, GENG Pinglan, CAO Jianxin. Regulation of Gypsum Crystalline and Morphology in Ca(H2PO4)2-H3PO4-K2SO4 System[J]. Journal of Synthetic Crystals, 2021, 50(6): 1104
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Received: Mar. 9, 2021
Accepted: --
Published Online: Aug. 23, 2021
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