Study On Solid-liquid Equilibrium Of K⁺,NH₄⁺//Cl^-,H₂PO₄^-,（NH₂）₂CO-H₂O At 313.15

The isothermal dissolution equilibrium method is used to determine the solubility data of interactive quinary system NH₄⁺,K⁺//Cl^-,H₂PO₄^-,（NH₂）₂CO-H₂O and some of its sub-systems at 313.15K,and the corresponding isothermal phase diagram and water diagram are drawn,schreinermark wet slag method and X-ray diffraction method is used to identify the composition of equilibrium solid phase.which can provide theoretical support for the subsequent crystallization process research.The results show that:（1）Ternary system KH₂PO₄-（NH₂）₂CO-H₂O and quaternary system NH₄⁺,K⁺//H₂PO₄^-,（NH₂）₂CO-H2O are both simple systems with a common saturation point.The phase diagram of ternary system KH₂PO₄-（NH₂）₂CO-H₂O contains two univariate curves,two crystallization regions,and（NH₂）₂CO has a strong salting out effect on KH₂PO₄.There are three univariate curves and three crystallization zones in the phase diagram of the quaternary system NH₄⁺,K⁺//H₂PO₄^-,（NH₂）₂CO-H₂O,the solid solution[K_x（NH₄）_1-x]H₂PO₄ of K⁺and NH₄⁺is formed in the course of dissolving the system to equilibrim.According to the water diagram of the substance,the water content is positively correlated with the content of KH₂PO₄ and NH₄H₂PO₄,and negatively correlated with that of（NH₂）₂CO.（2）The ternary system NH₄Cl-（NH₂）₂CO-H₂O and the quaternary system NH₄⁺//Cl^-,H₂PO₄^-,（NH₂）₂CO-H₂O are both simple system with two common saturation points.In addition,in the process of dissolution to equilibrium,the heterogeneous compound salt NH₄Cl·（NH₂）₂CO is formed.In the phase diagram of ternary system NH₄Cl-（NH₂）₂CO-H₂O,there are two univariate curves and the five crystallization regions.And there is mutual salt dissolution between NH₄Cl and（NH₂）₂CO.In the phase diagram of quaternary system NH₄⁺//Cl^-,H₂PO₄^-,（NH₂）₂CO-H₂O,there are four univariate curves and four crystallization regions.The water diagram with substance shows that water content is positively correlated with NH₄H₂PO₄ content and negatively correlated with NH₄Cl and（NH₂）₂CO content.（3）The interactive quinary system NH₄⁺,K⁺//Cl^-,H₂PO₄^-,（NH₂）₂CO-H₂O is a complex system,in which there is double decomposition reaction between NH₄⁺,K⁺//Cl^-and H₂PO₄^-interaction salt pairs.In the phase diagram of quinary system NH₄⁺,K⁺//Cl^-,H₂PO₄^-,（NH₂）₂CO-H₂O,there are nine common saturation points and nine univariate curves,the solid solution（K,NH₄）Cl and（NH₄,K）Cl of KCl and NH₄Cl,solid solution[K_x（NH₄）_1-x]H₂PO₄ of KH₂PO₄ and NH₄H₂PO₄,double salt NH₄Cl·（NH₂）₂CO of NH₄Cl and（NH₂）₂CO are formed during the dissolution of the quinary system to equilibrium.According to the water diagram of NH₄⁺,Cl^-and（NH₂）₂CO,the water content is negatively correlated with the content of NH₄⁺,Cl^-and（NH₂）₂CO in the system,especially with the increase of the content of（NH₂）₂CO,the water content decreases sharply.The solubility data of the ternary system KH₂PO₄-（NH₂）₂CO-H₂O and NH₄Cl-（NH₂）₂CO-H₂O at 313.15K were calculated by using Wilson and NRTL models.The results showed that:In the calculation results of ternary system KH₂PO₄-（NH₂）₂CO-H₂O and NH₄Cl-（NH₂）₂CO-H₂O,the root mean-square deviation（RMSD）of Wilson model is 0.75 and 0.85,and the relative average deviation（RAD）is 3.12%and 2.26%,respectively.The root mean-square deviation（RMSD）of NRTL model is 1.53 and1.38,and the relative average deviation（RAD）is 9.31%and 2.93%,respectively,indicating that both models are applicable to the ternary immiscible system of electrolyte and non-electrolyte in this paper.