| In this paper,research on the solid-liquid phase equilibrium of KCl-NH4H2PO4-CO?NH2?2-H2O system at 283.15K,the solubility data was obtained,and the phase diagram is drawn.It provides a theoretical basis for the subsequent phase equilibrium and co-crystallization studies.KCl-NH4H2PO4-CO?NH2?2-H2O system is a complex quinary reciprocal system,KCl and NH4H2PO4 happen a reversible metathesis reaction,and NH4Cl and KH2PO4were produced,so there are five kinds of experimental materials in the system:KCl;NH4H2PO4;NH4Cl;KH2PO4 and CO?NH2?2.In the system,due to the similar ionic radius of NH4+and K+,the two cations combined with Cl-and H2PO4-anions,respectively,four solid solutions:?K,NH4?H2PO4,?NH4,K?H2PO4,?NH4,K?Cl,?K,NH4?Cl will have formed.The reaction of urea with NH4Cl will form double salt CO?NH2?2意H4Cl.Na+,K+//NO3-,H2PO4-,CO?NH2?2-H2O and KCl-NH4H2PO4-CO?NH2?2-H2O all belong to interactive system,but K+ion radius is larger than Na+ion radius,Na+,K+//NO3-,H2PO4-,CO?NH2?2-H2O system will be no formed solid solution and hydrate,which belongs to a simple urea-containing interactive system.Due to four solid solutions and double salts were formed in KCl-NH4H2PO4-CO?NH2?2-H2O system,it is difficult to draw the phase diagram,according to the situation,it can be simplified.KCl-NH4H2PO4-CO?NH2?2-H2O system at 283.15K phase equilibrium is studied by the isothermal dissolution equilibrium method.The principle that the advanced system adds another substance based on the co-saturation point of the secondary subsystem at 283.15K,under constant temperature conditions,solid-liquid phase equilibrium is reached after a long time of dissolution and stirring.The phase equilibrium of this system at 283.15K,in addition to five binary sub-systems had been reported,there are eight ternary sub-systems,five quaternary sub-systems,and a general system,among them,the ternary sub-system:CO?NH2?2-NH4H2PO4-H2O;CO?NH2?2-KCl-H2O;KCl-KH2PO4-H2O;NH4Cl-NH4H2PO4-H2O;NH4Cl-KCl-H2O;NH4H2PO4-KH2PO4-H2O and quaternary interaction sub-system:K+,NH4+//Cl-,H2PO4--H2O had been determined by ours research group in the early stage.The following seven systems:ternary systems:KH2PO4-CO?NH2?2-H2O;CO?NH2?2-NH4Cl-H2O;quaternary systems:NH4+//Cl-,H2PO4-,CO?NH2?2-H2O;K+//Cl-,H2PO4-,CO?NH2?2-H2O;NH4+,K+//Cl-,CO?NH2?2-H2O;NH4+,K+//H2PO4-,CO?NH2?2-H2O;general system:KCl-NH4H2PO4-CO?NH2?2-H2O had been obtained their solubility data,and these phase diagram were drawn,in this paper.The research shows that:It is a simple ternary system of the KH2PO4-CO?NH2?2-H2O,and only one co-saturated crystallization point,two univariate curves,and four regions:unsaturated region,CO?NH2?2 crystallization region,KH2PO4 crystallization region,mixed crystallization region of CO?NH2?2 and KH2PO4.It is a complex ternary system of the CO?NH2?2-NH4Cl-H2O,double salt CO?NH2?2意H4Cl have been formed in the equilibrium solid phase of the system,and the crystallization region than simple system more than two crystallization region.There are two co-saturation crystallization points,two univariate curves and six regions:unsaturated region,CO?NH2?2 crystallization region,NH4Cl crystallization region,mixed crystallization region of CO?NH2?2意H4Cl and CO?NH2?2,mixed crystallization region of CO?NH2?2意H4Cl and NH4Cl,and double salt CO?NH2?2意H4Cl crystallization region.It is a simple quaternary system of the K+//Cl-,H2PO4-,CO?NH2?2-H2O,there are three ternary sub-systems,three univariate curves and three crystallization regions:CO?NH2?2 crystallization region,KH2PO4 crystallization region and KCl crystallization region for the dry salt phase diagramThere are three ternary sub-systems of quaternary system NH4+,K+//H2PO4-,CO?NH2?2-H2O,and solid solution?NH4,K?H2PO4 base of NH4H2PO4 and solid solution?K,NH4?H2PO4 base of KH2PO4were formed in the equilibrium solid phase.The phase diagram have a co-saturation crystallization point,three univariate curves,and three crystallization regions:solid solution?K,NH4?H2PO4 crystallization region,solid solution?NH4,K?H2PO4 crystallization region,and CO?NH2?2 crystallization regions.Quaternary system NH4+//Cl-,H2PO4-,CO?NH2?2-H2O owns three ternary sub-systems,which three ternary sub-systems CO?NH2?2-NH4Cl-H2O has two co-saturation crystallization points,so the dry salt phase diagram of NH4+//Cl-,H2PO4-,CO?NH2?2-H2O system is a complex system at 283.15K,which contains two co-saturation crystallization points,four univariate curves,four crystallization regions:CO?NH2?2 crystallization region,NH4Cl crystallization region,NH4H2PO4crystallization region,and double salt CO?NH2?2意H4Cl crystallization region.Double salt and two solid solutions were formed in the equilibrium solid phase of NH4+,K+//Cl-,CO?NH2?2-H2O system.The dry salt phase diagram of NH4+,K+//Cl-,CO?NH2?2-H2O system which contains three co-saturation crystallization points,four univariate curves,and four crystallization regions:CO?NH2?2 crystallization region,double salt CO?NH2?2意H4Cl crystallization region,solid solution?NH4,K?Cl base of NH4Cl crystallization region and solid solution?K,NH4?Cl base of KCl crystallization region.Four quaternary sub-systems are studied in this paper,and all own seven co-saturation crystallization points.In early research,the quaternary NH4+,K+//Cl-,H2PO4--H2O reciprocal system which contains two co-saturation crystallization points,so there are nine research direction in the quinary system.There are double salt CO?NH2?2意H4Cl and four partially miscible solid solutions:?K,NH4?H2PO4,?NH4,K?H2PO4,?K,NH4?Cl,?NH4,K?Cl were formed in the equilibrium solid phase of the quinary system.Four ions produce interactions with each other,and the concentration of each ion are influenced each other.This ternary system include nine co-saturated crystallization points,nine univariate curves,and the NH4+-Cl-dry salt diagrams,which similar to the quaternary interactive system dry salt diagrams,but with six crystallization regions:solid solution?NH4,K?Cl crystallization region,solid solution?K,NH4?Cl crystallization region,solid solution?K,NH4?H2PO4 crystallization region,solid solution?NH4,K?H2PO4 crystallization region,CO?NH2?2 crystallization region and double salt CO?NH2?2意H4Cl crystallization region.Three electrolyte theoretical models:Pitzer model,NRTL model and Wilson model are applied to study theory of multicomponent solid-liquid phase equilibrium.In this paper,three models were used to correlation the experimented data of the KH2PO4-CO?NH2?2-H2O system.The experimented data of CO?NH2?2-NH4Cl-H2O and K+//Cl-,H2PO4-,CO?NH2?2-H2O systems are correlation by Pitzer model,and the experimented data compared with the theoretical model,the results are highly consistent. |
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