Study On Phase Equilibrium Of KCl-NH₄H₂PO₄-（NH₂）₂CO-H₂O System At 353.15K

In this paper,the isothermal dissolution equilibrium method is used to study the solid-liquid equilibrium of five-component water salt system KCl-NH₄H₂PO₄-（NH₂）₂CO-H2O including sub-system and the solid-liquid equilibrium of the total system at 353.15K,respectively.those sub-system are the ternary system NH₄H₂PO₄-（NH₂）₂CO-H₂O,（NH₂）₂CO-NH₄Cl-H₂O,NH₄H₂PO₄-NH₄Cl-H₂O;NH₄⁺,K⁺//H₂PO₄^-,（NH₂）₂CO-H₂O,NH₄⁺//Cl^-,H₂PO₄^-,（NH₂）₂CO-H₂O;The solubility data of the relevant systems were measured,an isothermal phase diagram was drawn based on the experimental data,and the equilibrium solid phase composition of each system obtained in the experiment was determined by the wet slag method and X-ray diffraction method.The research results show that:（1）The ternary system NH₄H₂PO₄-（NH₂）₂CO-H₂O is a simple co-saturated system.There are a common saturation point,no double salt and solid solution formation,and 2 univariate curves in this system.The isothermal phase diagram is divided into 4 phases in this system.The zones are NH₄H₂PO₄crystallization zone,（NH₂）₂CO crystallization zone,NH₄H₂PO₄and（NH₂）₂CO co-saturation zone,and unsaturated zone.According to the phase diagram shows that,（NH₂）₂CO has a strong salting-out effect on NH₄H₂PO₄;ternary system NH₄H₂PO₄-NH₄Cl-H₂O is also a simple co-saturation system.The system has a common saturation point,no double salt and solid solution are formed.There are two univariate curves.The isothermal phase diagram is divided into four phase regions:NH₄H₂PO₄crystallization regions,NH₄Cl crystallization zone,NH₄H₂PO₄and NH₄Cl co-saturation zone,unsaturated zone,NH₄Cl has a strong salting-out effect on NH₄H₂PO₄;The ternary system（NH₂）₂CO-NH₄Cl-H₂O is a complex system.The equilibrium solid phase of the system produces double salt（NH₂）₂CO·NH₄Cl,and there are two common saturation points.The system has two univariate curves.There are 6 phase regions,namely.（NH₂）₂CO crystallization region,NH₄Cl crystallization region,（NH₂）₂CO·NH₄Cl crystallization region,（NH₂）₂CO and（NH₂）₂CO·NH₄Cl crystallization region,NH₄Cl and（NH₂）₂CO·NH₄Cl crystallization zone,unsaturated zone.（2）The quaternary system NH₄⁺,K⁺//H₂PO₄^-,（NH₂）₂CO-H₂O will produce solid solutions.The phase diagram of this system has a common saturation point,three univariate curves,and three crystallization regions.In the quaternary system NH₄⁺//Cl^-,H₂PO₄^-,（NH₂）₂CO-H₂O,（NH₂）₂CO and NH₄Cl will form a double salt（NH₂）₂CO·NH₄Cl.The system has two co-saturated crystallization points,four univariate curves divide the isothermal phase diagram into four phase regions:（NH₂）₂CO crystallization region,NH₄Cl crystallization region,NH₄H₂PO₄crystallization region,and double salt（NH₂）₂CO·NH₄Cl crystallization region.（3）The the reciprocal quinary system KCl-NH₄H₂PO₄-（NH₂）₂CO-H₂O has 9co-saturated crystallization points.So the experiments is fed from 9 directions,and there are double salt（NH₂）₂CO·NH₄Cl,four partially miscible solid solutions:（NH₄,K）H₂PO₄,（K,NH₄）H₂PO₄,（K,NH₄）Cl,（NH₄,K）Cl in this system.Two forms of phase diagrams are used to express the content for this system.One is to omit the least soluble salt KCl in the system and convert it into a dry basis phase diagram of NH₄⁺-H₂PO₄^--（NH₂）₂CO.There are 9 total phase diagrams in this phase diagram.Saturated crystallization point,7 univariate curves,6 crystallization areas;the other is a simplified dry salt diagram assuming（NH₂）₂CO saturation,this phase diagram has 9co-saturated crystallization points,9 univariate curves,and 10 Crystallization area.