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SCI和EI收录∣中国化工学会会刊

Chinese Journal of Chemical Engineering ›› 2025, Vol. 78 ›› Issue (2): 93-107.DOI: 10.1016/j.cjche.2024.11.002

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Solid-liquid phase diagram of the KNO3-Ca(NO3)2-Mg(NO3)2-H2O system at 313.15 K

Xiangxia Zeng, Tao Zhang, Li Lv, Wenxiang Tang, Zongpeng Zou, Shengwei Tang   

  1. Multi-phase Mass Transfer and Reaction Engineering Laboratory, School of Chemical Engineering, Sichuan University, Chengdu 610065, China
  • Received:2024-07-31 Revised:2024-09-30 Accepted:2024-11-04 Online:2024-12-30 Published:2025-02-08
  • Supported by:
    We are grateful for the financial support from the National Key Research and Development Program of China (2022YFC2904704) and the Fundamental Research Funds for the Central Universities (SCU2024D009).

Solid-liquid phase diagram of the KNO3-Ca(NO3)2-Mg(NO3)2-H2O system at 313.15 K

Xiangxia Zeng, Tao Zhang, Li Lv, Wenxiang Tang, Zongpeng Zou, Shengwei Tang   

  1. Multi-phase Mass Transfer and Reaction Engineering Laboratory, School of Chemical Engineering, Sichuan University, Chengdu 610065, China
  • 通讯作者: Shengwei Tang,E-mail:tangdynasty@scu.edu.cn
  • 基金资助:
    We are grateful for the financial support from the National Key Research and Development Program of China (2022YFC2904704) and the Fundamental Research Funds for the Central Universities (SCU2024D009).

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109

Abstract: The enrichment of low-grade phosphate rock is an important process to realize sustainable support of phosphorus resources. An aqueous solution containing Ca(NO3)2 and Mg(NO3)2 is produced during the enrichment of low-grade phosphate rock by leaching of HNO3 or calcination coupling with leaching of NH4NO3 solution. Preparation liquid fertilizer is a preferential way to utilize it. The liquid-solid phase diagrams of Ca(NO3)2-Mg(NO3)2-H2O, KNO3-Mg(NO3)2-H2O, KNO3-Ca(NO3)2-H2O and KNO3-Ca(NO3)2-Mg(NO3)2-H2O systems at 313.15 K were studied by isothermal dissolution equilibrium method. Two crystallization regions of Ca(NO3)2·4H2O and Mg(NO3)2·6H2O were observed in the phase diagram of the ternary system Ca(NO3)2-Mg(NO3)2-H2O, a liquid fertilizer with a maximal total nutrient content of 27.46% and a nutrients ratio of N:Ca:Mg = 8.40:10.37:1 can be formed. A homogenous solution can be formed by mixing Ca(NO3)2·4H2O and Mg(NO3)2·6H2O. In the ternary system KNO3-Mg(NO3)2-H2O, the crystallization regions of KNO3, Mg(NO3)2·6H2O and the co-crystallization region of KNO3 and Mg(NO3)2·6H2O were observed. The obtained maximal total nutrient content of liquid fertilizer is 23.32% with the ratio of N:K2O = 1:3.39. In the ternary system KNO3-Ca(NO3)2-H2O, the crystallization regions of Ca(NO3)2·4H2O and KNO3 were observed. The obtained maximal total nutrient content of liquid fertilizer is 38.41% with the ratio of N:K2O:Ca = 1.05:1.18:1. A homogenous solution can also be formed by mixing Ca(NO3)2·4H2O and KNO3 directly. In the quaternary system KNO3-Ca(NO3)2-Mg(NO3)2-H2O, the crystallization regions of Ca(NO3)2·4H2O, Mg(NO3)2·6H2O and KNO3 and the co-crystallization region of KNO3 and Mg(NO3)2·6H2O were observed. The obtained maximal total nutrient content of liquid fertilizer is 38.41% with the ratio of N:K2O:Ca = 1.05:1.18:1. The modified BET model was successfully used to fit the solubility curves. The results can provide a guidance for the formulation of water-soluble fertilizers of N-(K, Ca, Mg).

Key words: Calcium nitrate, Magnesium nitrate, Liquid water-soluble fertilizer, Phase equilibria, BET model

摘要： The enrichment of low-grade phosphate rock is an important process to realize sustainable support of phosphorus resources. An aqueous solution containing Ca(NO3)2 and Mg(NO3)2 is produced during the enrichment of low-grade phosphate rock by leaching of HNO3 or calcination coupling with leaching of NH4NO3 solution. Preparation liquid fertilizer is a preferential way to utilize it. The liquid-solid phase diagrams of Ca(NO3)2-Mg(NO3)2-H2O, KNO3-Mg(NO3)2-H2O, KNO3-Ca(NO3)2-H2O and KNO3-Ca(NO3)2-Mg(NO3)2-H2O systems at 313.15 K were studied by isothermal dissolution equilibrium method. Two crystallization regions of Ca(NO3)2·4H2O and Mg(NO3)2·6H2O were observed in the phase diagram of the ternary system Ca(NO3)2-Mg(NO3)2-H2O, a liquid fertilizer with a maximal total nutrient content of 27.46% and a nutrients ratio of N:Ca:Mg = 8.40:10.37:1 can be formed. A homogenous solution can be formed by mixing Ca(NO3)2·4H2O and Mg(NO3)2·6H2O. In the ternary system KNO3-Mg(NO3)2-H2O, the crystallization regions of KNO3, Mg(NO3)2·6H2O and the co-crystallization region of KNO3 and Mg(NO3)2·6H2O were observed. The obtained maximal total nutrient content of liquid fertilizer is 23.32% with the ratio of N:K2O = 1:3.39. In the ternary system KNO3-Ca(NO3)2-H2O, the crystallization regions of Ca(NO3)2·4H2O and KNO3 were observed. The obtained maximal total nutrient content of liquid fertilizer is 38.41% with the ratio of N:K2O:Ca = 1.05:1.18:1. A homogenous solution can also be formed by mixing Ca(NO3)2·4H2O and KNO3 directly. In the quaternary system KNO3-Ca(NO3)2-Mg(NO3)2-H2O, the crystallization regions of Ca(NO3)2·4H2O, Mg(NO3)2·6H2O and KNO3 and the co-crystallization region of KNO3 and Mg(NO3)2·6H2O were observed. The obtained maximal total nutrient content of liquid fertilizer is 38.41% with the ratio of N:K2O:Ca = 1.05:1.18:1. The modified BET model was successfully used to fit the solubility curves. The results can provide a guidance for the formulation of water-soluble fertilizers of N-(K, Ca, Mg).

关键词: Calcium nitrate, Magnesium nitrate, Liquid water-soluble fertilizer, Phase equilibria, BET model

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