Study On Phase Equilibrium Of Nitrate-containing Birne In Xinjiang At Low Temperatures

In this work, the liquid-solid phase of quaternary system Na+//Cl-, SO42-,NO3--H2O, to which the brine system containing nitrate in Xinjiang belong, wasstudied by isothermal dissolution equilibrium method at low temperatures.Solubilities and density have been obtained at278.16K,273.16K,268.16K and258.16K. According to experimental data, the phase diagram, dry salt diagram, waterdiagram, the separation diagram of crystallization-region and composition-densitydiagram were drawn. Analysis were made on phase diagrams at differenttemperatures. Based on these studies above, salt crystallization regulation and routefor the brine with different composition were researched in the natural coolingprocess, and were compared with the artificial cooling process.The results show:In the equilibrium phase diagram of quaternary system Na+//Cl-, SO42-,NO3--H2O at278.16K,273.16K,268.16K and258.16K, no complex salt is formed,and there are three univariate curve with two salts corresponding to NaCl(NaCl·2H2O)-Na2SO4·10H2O, NaCl(NaCl·2H2O)-NaNO3, NaNO3-Na2SO4·10H2O,three crystalline regions with one salt corresponding to Na2SO4·10H2O,NaCl(NaCl·2H2O) and NaNO3, and a invariant point with three salts corresponding toNaCl(NaCl·2H2O), NaNO3and Na2SO4·10H2O.In the equilibrium phase diagram of these systems at278.16K,273.16K,268.16K and258.16K, as the temperature drops, Na2SO4·10H2O crystallizationregion becomes larger, NaCl(NaCl·2H2O) and NaNO3crystallization regions arerelatively narrow.In the natural cooling process, saturated solution with different composition willhave different crystallization routes. For the brine with the composition of theinvariant point, as the temperature decreases, three salts always saturated andprecipitated, but the changes of liquid composition are determined by three salt crystallization rate. Comparing artificial cooling process with natural cooling, thecrystallization regulation in artificial cooling process is similar to that in the naturalcooling process, the main difference is that impact of different cooling rates on thesolubility of salts.