Regulation of Gypsum Crystalline and Morphology in Ca(H2PO4)2-H3PO4-K2SO4 System

Abstract

Abstract: 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, SO^2-₄ 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 SO^2-₄ 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 ℃, SO^2-₄ 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.

Key words: α-CaSO₄·0.5H₂O, Ca(H₂PO₄)₂-H₃PO₄-K₂SO₄ system, gypsum, crystalline, morphology, regulation

CLC Number:

O782

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): 1104-1111.

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Regulation of Gypsum Crystalline and Morphology in Ca(H₂PO₄)₂-H₃PO₄-K₂SO₄ System

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