Phase Equilibria For The Alkali-metal Bicarbonate-containing Aqueous Systems At 273.15K

Carbonated salt lakes are mainly distributed in Tibet,China,and primarily belong to the carbonate or bicarbonate brine system.Phase diagrams can guide the utilization and production of salt-lake resources.The temperature difference in the salt lake area varies greatly,and there are a lot of studies about phase diagrams at room temperature and high temperature.Still,the low-temperature phase diagrams involving the bicarbonate systems are scarce.In this thesis,those works,including the phase equilibria of the quaternary system（Na⁺,K⁺,Cs⁺//HCO₃^-–H₂O）and its subsystem,the quaternary system（Na⁺,Cs⁺//Cl^-,HCO₃^-–H₂O）and its subsystem,the quaternary system（Na⁺,K⁺//Cl^-,HCO₃^-–H₂O）and its subsystem were studied.Solubilities and the physicochemical properties（such as density and refractive index）were determined,and the coexisted solid phases were identified.So,the solubility and physicochemical changing rules of the systems were obtained.The main results are as follows:In the simple quaternary system（Na⁺,K⁺,Cs⁺//HCO₃^-–H₂O）:the phase diagram of the ternary system（Na⁺,Cs⁺//HCO₃^-–H₂O）at 273.15 K has one invariant point（Na HCO₃+Cs HCO₃）,two univariant solubility curves and two single-salt crystallizing regions,corresponding to Na HCO₃ and Cs HCO₃.The phase diagram of the quaternary system（Na⁺,K⁺,Cs⁺//HCO₃^-–H₂O）at 273.15 K has one invariant point（Na HCO₃+KHCO₃+Cs HCO₃）,three univariant solubility curves and three single salt crystallizing regions corresponding to Na HCO₃,KHCO_3,and Cs HCO₃.The density and refractive index of the liquid phase change regularly with the composition in the equilibrium liquid phases.In the quaternary system（Na⁺,Cs⁺//Cl^-,HCO₃^-–H₂O）:the phase diagram of the ternary system（Na⁺,Cs⁺//Cl^-–H₂O）at 273.15 K has two invariant points(Na Cl+Cs Cl·2Na Cl·2H₂O;Cs Cl·2Na Cl·2H₂O+[Cs_1-x（Na·H₂O）_x]Cl),three univariant solubility curves,one single salt crystallizing region（Na Cl）,one double salt crystallizing region（Cs Cl·2Na Cl·2H₂O）and one solid solution crystallizing region([Cs_1-x（Na·H₂O）_x]Cl).The phase diagram of the quaternary system（Na⁺,Cs⁺//Cl^-,HCO₃^-–H₂O）at 273.15 K has three invariant points(Na Cl+Cs Cl·2Na Cl·2H₂O+Na HCO₃;Na HCO₃+Cs Cl·2Na Cl·2H₂O+[Cs_1-x（Na·H₂O）_x]Cl;[Cs_1-x（Na·H₂O）_x]Cl+Cs HCO₃+Na HCO₃),seven univariant solubility curves,three single salt crystallizing regions（Na Cl,Na HCO₃,Cs HCO₃）,one double salt crystallizing region（Cs Cl·2Na Cl·2H₂O）and one solid solution crystallizing region([Cs_1-x（Na·H₂O）_x]Cl).The density and refractive index of the liquid phase change regularly with the composition in the equilibrium liquid phases.In the quaternary system（Na⁺,K⁺//Cl^-,HCO₃^-–H₂O）at 273.15 K:the phase diagram has one invariant point（KHCO₃+KCl）,two univariant solubility curves,and two single salt crystallizing regions,corresponding to KHCO₃ and KCl.The quaternary system（Na⁺,K⁺//Cl^-,HCO₃^-–H₂O）at 273.15 K has two invariant points（Na Cl+KCl+Na HCO₃;KCl+Na HCO₃+KHCO₃）,five univariant solubility curves and four single salt crystallizing regions corresponding to Na Cl,Na HCO₃,KHCO₃ and KCl.The density and refractive index of the liquid phase change regularly with the composition in the equilibrium liquid phases.