Ca （H2PO4） 2-H3PO4-K2SO4体系两步法制备KH2PO4过程中硫酸钙晶型和形貌调控

doi:10.3969/j.issn.1001-1803.2022.11.004

Abstract

Abstract:

In Ca（H₂PO₄） ₂-H₃PO₄-K₂SO₄ system, α-calcium sulfate was made as a by-product during the production of KH₂PO₄through regulating the two-step crystallization reaction including the crystallization of CaSO₄·2H₂O at lower temperature and the crystal transformation from CaSO₄·2H₂O to CaSO₄·0.5H₂O at higher temperature. The effects of reaction conditions on the crystal formation and morphology of CaSO₄, the yields of phosphorus and potassium, and the decalcification rate in the two-step crystallization process were studied. The results showed that, the preparation parameters such as reaction temperature, reaction time, K₂SO₄ solution concentration, SO₄^2- excess coefficient, CaO/P₂O₅ molar ratio and P₂O₅ content significantly influenced the morphology of CaSO₄ crystal, the yields of phosphorus and potassium, and the decalcification rate. When the first-step reaction and crystallization was operated at 70 ℃ for 60 min and the second-step crystallization transformation was operated at 102 ℃ for 5.0 h under the conditions of K₂SO₄ concentration being 10%, SO₄^2- excess coefficient of 1.2, CaO/P₂O₅ ratio of 0.20 and P₂O₅ content of 25%, the yield of potassium and the yield of phosphorus and the decalcification rate of filtrate were 98.35%, 91.43% and 89.74%, respectively. The crystal form of the gypsum sample thus prepared was α-CaSO₄·0.5H₂O, and the morphology was hexagonal conical short column. The 2-hour-flexural-strength and absolute dry compressive strength reached 5.70 MPa and 35.07 MPa, respectively, which matched with the α30 level of the α-high-strength gypsum industry standard. The purity of the produced potassium dihydrogen phosphate was higher than 80%.

Key words: Ca（H₂PO₄）₂-H₃PO₄-K₂SO₄ system, one-step crystallization, two-step crystal transformation

CLC Number:

TQ177

Ye Wencai,Wu Qin,Yi Yun,Yu Wen,Cao Jianxin. Regulation of crystal form and morphology of gypsum during two-step preparation of KH₂PO₄ via Ca（H₂PO₄） ₂-H₃PO₄-K₂SO₄ system[J].China Surfactant Detergent & Cosmetics, 2022, 52(11): 1169-1178.

Figures/Tables 21

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References 14

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指标	初凝/min	终凝/min	2 h抗折/MPa	绝干抗压/MPa
JC/T 2038－2010	≥3	≤30	≥4.0（α30等级）	≥30.0（α30等级）
样品	12	27	5.7	35.07

Regulation of crystal form and morphology of gypsum during two-step preparation of KH₂PO₄ via Ca（H₂PO₄） ₂-H₃PO₄-K₂SO₄ system

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Regulation of crystal form and morphology of gypsum during two-step preparation of KH2PO4 via Ca（H2PO4） 2-H3PO4-K2SO4 system

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Regulation of crystal form and morphology of gypsum during two-step preparation of KH₂PO₄ via Ca（H₂PO₄） ₂-H₃PO₄-K₂SO₄ system