Study On Solid-liquid Equilibrium Mulit-Component Sodium Salt System Based On F And P Recovery Of In Mixed Rare Earth Ore

China is rich in rare earth resources,which accounts for a large proportion of the total reserves in the world,and has a rich variety and excellent quality.The purpose of this experiment is to provide basic thermodynamic data for the extraction and separation of fluorine and phosphorus in alkali decomposition of rare earth smelting process.In this paper,the phase equilibrium of Na+//F-,CO3-,PO43"-H2O quaternary system is studied,the solubility of the quaternary system and its subsystems,the density,pH and salting out rate of liquid phase are measured,and the corresponding phase diagram is drawn,which is used as the theoretical basis for the crystallization and separation method of sodium fluoride phosphate,and the isothermal evaporation analysis is carried out by using the phase diagram theory,so as to guide the separation of sodium fluoride phosphate,The purity of the extract is also very high.According to the phase diagram,the corresponding crystallization zone was divided,and the equilibrium solid phase was determined by wet slag method,which was proved by XRD.The results are as follows:The study of ternary phase diagram shows that at 313.15k,the NaF-Na2CO3-H2O ternary system has only two solid-phase regions,namely NaF,Na2CO3·H2O and one liquid-phase region,which belong to simple ternary system;the co saturation point of two salts is(NaF+Na2CO3·H2O);the crystal region of NaF is small,which is not easy to precipitate,and the crystal region of Na2CO3·H2O is large,which is easy to precipitate.Na3PO4-Na2CO3-H2O ternary system is a complex ternary system.There are two salt saturation points and three solid-phase areas.The solid salts are Na2CO3·H2O,Na3PO4·12H2O and Na4(CO(PO3)2)(H2O)2.The Double salt Na4(CO(PO3)2)(H2O)2 is formed.The Double salt is a Heterogenous compound salt,and the solid-phase area of the Double salt is small.The Co-saturated point Ei and E2 are Na4(CO(PO3)2)(H2O)2+Na3PO4·12H2O and Na4(CO(PO3)2)(H2O)2+Na2CO3·H2O,respectively.Na3PO4-NaF-H2O ternary system is also a complex ternary system.There are two salt saturation points and three solid-phase areas.The solid salt is NaF,Na3PO4·12H2O and Na7F(PO4)2·19H2O.The Double salt Na7F(PO4)2·19H2O is generated.The compound salt is a complex salt with different components,and the solid-phase area of the compound salt is very small.The co saturation points Ei and E2 are Na7F(PO4)2·19H2O+NaF and Na7F(PO4)2·19H2O+Na3PO4·12H2O,respectively.Therefore,in the process of wastewater recovery,attention should be paid to the control of water evaporation to avoid the reduction of the purity of the extract caused by the re salting out.It is found that there are two kinds of complex salts Na4(CO(PO3)2)(H2O)2 and Na7F(PO4)2·19H2O in the Quaternary System Na+//F-,CO3-,PO43--H2O at 313.15k,and there are two co saturation points,five single salt crystallization areas and six single variable double solid co saturation lines in the dry salt diagram.The crystallization area of NaF is the largest,and that of Na7F(PO4)2·19H2O is the smallest,which indicates that the effect of complex salt on the recovery of fluorine and phosphorus is small,and the phosphorus in the washing solution is precipitated in the form of Na3PO4·12H2O.