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(NO_(3))_(2) and Mg(NO_(3))_(2) is produced during the enrichment of low-grade phosphate rock by leaching of HNO_(3) or calcination coupling with leaching of NH_(4)NO_(3) solution. Preparation liquid fertilizer is a preferential way to utilize it. The liquid−solid phase diagrams of Ca(NO_(3))_(2)-Mg(NO_(3))_(2)-H_(2)O, KNO_(3)-Mg(NO_(3))_(2)-H_(2)O, KNO_(3)-Ca(NO_(3))_(2)-H_(2)O and KNO_(3)-Ca(NO_(3))_(2)-Mg(NO_(3))_(2)-H_(2)O systems at 313.15 K were studied by isothermal dissolution equilibrium method. Two crystallization regions of Ca(NO_(3))_(2)·4H_(2)O and Mg(NO_(3))_(2)·6H_(2)O were observed in the phase diagram of the ternary system Ca(NO_(3))_(2)-Mg(NO_(3))_(2)-H_(2)O, 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(NO_(3))_(2)·4H_(2)O and Mg(NO_(3))_(2)·6H_(2)O. In the ternary system KNO_(3)-Mg(NO_(3))_(2)-H_(2)O, the crystallization regions of KNO_(3), Mg(NO_(3))_(2)·6H_(2)O and the co-crystallization region of KNO_(3) and Mg(NO_(3))_(2)·6H_(2)O were observed. The obtained maximal total nutrient content of liquid fertilizer is 23.32% with the ratio of N:K_(2)O = 1:3.39. In the ternary system KNO_(3)-Ca(NO_(3))_(2)-H_(2)O, the crystallization regions of Ca(NO_(3))_(2)·4H_(2)O and KNO_(3) were observed. The obtained maximal total nutrient content of liquid fertilizer is 38.41% with the ratio of N:K_(2)O:Ca = 1.05:1.18:1. A homogenous solution can also be formed by mixing Ca(NO_(3))_(2)·4H_(2)O and KNO_(3) directly. In the quaternary system KNO_(3)-Ca(NO_(3))_(2)-Mg(NO_(3))_(2)-H_(2)O, the crystallization regions of Ca(NO_(3))_(2)·4H_(2)O, Mg(NO_(3))_(2)·6H_(2)O and KNO_(3) and the co-crystallization region of KNO_(3) and Mg(NO_(3))_(2)·6H_(2)O were observed. The obtained maximal total nutrient content of liquid fertilizer is 38.41% with the ratio of N:K_(2)O: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).
基金
support from the National Key Research and Development Program of China(2022YFC2904704)
the Fundamental Research Funds for the Central Universities(SCU2024D009)。
