The Liquid-solid Phase Equilibria Of The System Na⁺, K⁺, Mg²⁺∥Cl^-, NO₃^--H₂O At 298.16K

In this work, the liquid-solid phase equilibria of the system Na⁺, K⁺, Mg²⁺//Cl-, NO₃--H₂O and its subsystems Na⁺, K⁺, Mg²⁺//NO₃--H₂O and K⁺, Mg²⁺//Cl-, NO₃--H₂O at 298.16K are studied by isothermal method. According to solubilities mearsured, equilibrium phase diagrams, dry salt diagram and the corresponding water diagram of these systems at 298.16K are obtained. Study on them can provide theoretical guidance for the comprehensive utilization of the nitrate deposits in Xinjiang.The results show:In the phase diagram of Na⁺, K⁺, Mg²⁺// NO₃--H₂O at 298.16K, which is a quaternary salt-water system with a common anion, there are one invariant point with three salts, three univariant curves with two salt and three regions of crystallization with one salt corresponding to KNO₃,Mg(NO₃)2·6H₂O and NaNO₃. No reaction curve exists in univariant curves. Invariant point is co-crystallizing point.The phase diagram of the system K⁺, Mg²⁺//Cl-, NO₃--H₂O at 298.16K, which is a quaternary reciprocal water-salt system includes five crystallization regions corresponding to KCl, KNO₃, Mg(NO₃)2·6H₂O, KCl·MgCl2·6H₂O and MgCl2·6H₂O. The respective crystallization aeras are being separated from each other by seven univariant curves which intersect in three invariant points. Two reaction curves exist in seven univariant curves. One invariant point is co-crystallizing point, the others are reaction points.In the phase diagram of Na⁺, K⁺, Mg²⁺//Cl-, NO₃--H₂O system at 298.16K, which is a quinary salt-water system with three reciprocal salt-pair and the dry phase diagram of which can be plotted in form of a trigonal prism, there are four invariant points with four salts, and seven crystallization, one of which is complex salt. The seven crystallization regions are the ones of NaCl, KCl, NaNO₃, KNO₃, Mg(NO₃)2·6H₂O, MgCl2·6H₂O and KCl·MgCl2·6H₂O.