Solid And Liquid Phase Equilibrium Research For Na⁺,Mg²⁺//Cl^-,H₂PO₂^--H₂O Interactive Quaternary And Subsystem

Magnesium hypophosphite is an important hypophosphite, which has been used as flame retardant, drugs for the treatment of rheumatoid arthritis, plastic stabilizer,amendment of the soil and animal nutritional supplement. High purity magnesium hypophosphite can be synthesized via the double decomposition reaction between sodium hypophosphite and magnesium chloride. To improve the reaction yield, purity of the product and optimize the process, the relevant phase diagrams need to research. Our laboratory had determined the phase diagram of Na+, Mg2+ // Cl-, H2PO2--H2O interaction quaternary system at 298.15k. But the phase diagram data of this system at other temperature are not reported. In this paper, the phase diagram of Na+, Mg2+ // Cl-, H2PO2-?H2O interaction quaternary system and subsystem at 325.15k were researched. The results are as follows:1.In NaH2PO2-H2O binary system, the solid phase type is NaH2PO2 · H2O and the solubilities of NaH2POO · H2O in water increase with temperature changing .2.The Mg(H2PO2)2-NaH2PO2-H2O ternary system at 323.15 K is complex system,three solid salts of Mg(H2PO2)2·6H2O,NaH2PO2·H2O and one anhydrous double salt NaMg(H2PO2)3 were found. The diagram shows the double salt of NaMg(H2PO2)3 covers a very large solid-liquid equilibrium region, which indicate NaMg(H2PO2)3 can be formed easily. To prevent NaMg(H2PO2)3 generation influence the purity of the product,it's necessary to control the ratio while producing Mg(H2PO2)2 from NaH2PO2·H2O and MgCl2·6H2O.3.The Mg(H2PO2)2- MgCl2- H2O ternary system at 323.15 K is a complex system, four solid salts of Mg(H2PO2)2,Mg(H2POO)2·6H2O,MgCl2·6H2O and one double salt Mg2(H2PO2)2Cl2 6H2O occur in the system. (1) Mg2(H2PO2)2Cl2·6H2O is incompatible double salts (2) Magnesium hypophosphite hexahydrate transform to anhydrate magnesium hypophosphite (3) MgCl2·6H2O and Mg2(H2PO2)2Cl2 6H2O occupies a small SLE region.4.The system of Na+,Mg+//Cl-,H2PO2--H2O has seven solid phase area,seven eutectic point of two salt and four eutectic point of three salt. The solid phase area of magnesium hypophosphite and double salt NaMg(H2PO2)3 are the largest. This double salt can interfere the product yield and quality. So it's necessary to control the ratio of NaH2PO2 H2O to MgCl2·6H2O.