| Water Soluble Fertilizer has attracted more and more attention in the present agriculture.Because it can effectively reduce soil acidification,improve soil nutrient status and crop growth.KCl and（NH2）2CO are commonly used as raw materials for water soluble fertilizer production.At present,some studies on the phase equilibrium of system KCl-（NH2）2CO-H2O have been reported,but no studies on its co-crystallization have been reported.This paper mainly studies the thermodynamic properties,kinetic properties,crystallization process and technology of system KCl-（NH2）2CO-H2O,which is of great significance for the crystallization process of producing water soluble ertilizer containing N and K.The solubility data of ternary system KCl-（NH2）2CO-H2O at 303.15K,323.15K,333.15K and 343.15K were determined by isothermal solution equilibrium method.The obtained equilibrium solid phase was identified by wet slag method combined with X-ray diffraction（XRD）method.The phase and XRD patterns at different temperatures are drawn.The results show that the ternary system belongs to simple co-saturation system,and the trend of phase diagram is the same at different temperatures.There is one co-saturation point,two univariate curves and three crystallization zones.Using Wilson,the NRTL model to complete the related calculation for the solubility data of the system,including Wilson model calculation value of RAD,RMSD maximum 2.18×10-2and 0.83,NRTL model calculation value of RAD,RMSD maximum 1.69×10-2and 0.40,The results show that the two models are suitable for the system.The two models are used to predict the solubility data of the system at 283.15K,313.15K and 353.15K,and the prediction results are good.It provides basic data for the subsequent study of metastable zone and crystallization kinetics of the system.The metastable zone of ternary system KCl-（NH2）2CO-H2O was measured by laser in the temperature range of 313.15 to 353.15K.The experimental results show that the metastable zone width of the system was affected by different temperature and different components.Focused Beam Reflectance Measurement（FERM）and Particle Video Microscope（PVM）on-line monitoring techniques were used to measure the total particle number and average particle size during the co-crystallization process of ternary system KCl-（NH2）2CO-H2O.The suspension density was measured by differential weight method.Nucleation rate,growth rate and susaturation were calculated,and the crystallization kinetics equation was fitted.The results show that nucleation activation energy for 2.01×104J/mol,growth activation energy of 6.10×105J/mol,and the former is lower than the latter,indicating that temperature has a more obvious effect on the nucleation rate of ternary system KCl-（NH2）2CO-H2O.It provides a theoretical basis for the design of crystallization process of system KCl-（NH2）2CO-H2O.The cooling crystallization process of ternary system KCl-（NH2）2CO-H2O was studied,and XRD,Scanning Electron Microscope（SEM）and Energy Dispersive Spectrometry（EDS）were used to characterize the crystal products.The results show that there are KCl molecules and patterns protruding from the crystal surface,the results indicated that（NH2）2CO precipitates firstly during the crystallization process,and then KCl,and KCl grows on the surface of（NH2）2CO crystal.Finally,the crystal is a simple mixed crystal composed of KCl and（NH2）2CO.The crystallization process of ternary system KCl-（NH2）2CO-H2O was explored,the yield of the product was calculated,the composition of the sample was analyzed by XRD and chemical analysis,and the morphology of the crystal product was analyzed by SEM.It provides reference for optimizing crystallization process and actual production of the system. |
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