Phase Equilibrium And Applications Of Brine Containing Nitrate At Low Temperatures In Xinjiang

Xinjiang has abundant saline lake resources and a long cold winter, some researches show that brine can be separated by using cold energy in winter. Developing saline lake process at low temperature not only can save water, reduce consumption, but also can realize continuous production in winter. In this work, the solid-liquid phase equilibrium of the quinary system Na+,K+//Cl-,SO42-,NO3-―H2O and its one quaternary subsystem Na+,K+//Cl-,NO3-―H2O, to which utilization of nitrate brine in xinjiang belong, have been studied by isothermal method at 258.15 K and 273.15 K. Solubilities of each salt and densities of the solution in the quinary system saturated with Na Cl and its quaternary subsystems(except ice phase zone) were determined experimentally. According to experimental data, the phase diagram, dry salt diagram, separation diagram of crystallization-region, water diagram and composition-density diagram were drawn. Analysis were carried out on phase diagrams at three different temperatures. In order to solve the problem that many double salts crystallize in the processing of the salt lake brine, which results in the complex technology, the phase equilibria of different salt-water systems at different temperatures have been studied. The results show that:(1)The phase diagrams of the system Na+,K+//Cl-,NO3-―H2O have the same structures at 258.15K、273.15K、298.15 K and consist of four crystalline regions with single salt corresponding to Na NO3、Na Cl、KNO3 and KCl; five univariant curves corresponding to Na NO3+Na Cl、Na Cl+KNO3、KNO3+KCl、Na NO3+KNO3; and two invariant points corresponding to KCl+KNO3+Na Cl、Na NO3+KNO3+Na Cl. All the phase diagrams have no double salts, but there crystalline region size changes with temperature.(2)The phase diagram of the system Na+,K+//Cl-,SO42-,NO3-―H2O saturated with Na Cl at 258.15K、273.15 K consist of four crystallization regions corresponding to Na Cl+Na NO3, Na Cl+KNO3, Na Cl+KCl and Na Cl+Na2SO4?10H2O; five univariant curves corresponding to Na Cl+Na NO3+KNO3、Na Cl+Na NO3+Na2SO4?10H2O、Na Cl +KNO3+KCl 、 Na Cl+KNO3+Na2SO4?10H2O 、 Na Cl+KCl+Na2SO4?10H2O; two invariant points corresponding to Na Cl+Na NO3+KNO3+Na2SO4?10H2O、Na Cl+KCl+ KNO3+Na2SO4?10H2O. Compared with the phase diagram of the quinary system at 298.15 K, the crystalline regions of double salts Na NO3?Na2SO4?H2O and K3Na(SO4)2 disappear, the crystalline region of Na2SO4?10H2O becomes larger. As a result, the phase diagram of the quinary system is simplified greatly at 258.15 K.(3)For the salt-water systems with sulfate, crystalline regions of several sulfate double salts, which appear at room temperature, dot not disappear easily at high temperature, and sometimes, new sulfate double salts may generate; on the contrary, the low temperature can limit the generation of the sulfate double salts, and the crystalline regions of most of sulfate double salts disappear or reduce; for the double salts with nitrate and magnesium chloride, at high or low temperature, their crystalizing regions become small or disappear. This feature of phase equilibria of salt-water systems at low temperature is helpful to simplify the production process.