313.15K四元体系Na+//SO42-,CO32-,NO3--H2O固液相平衡研究

Solid-liquid equilibria of quaternary system Na+//SO42-,CO32-,NO3--H2O at 313.15 K

采用等温溶解法研究313.15K下四元体系Na^+//SO4^2-,CO3^2-,NO3^--H2O的固液相平衡关系。测定了平衡溶液的溶解度数据及物理性质数据,包括密度、黏度、折射率。根据实验数据,绘制了相应的干盐相图、水图及物理性质-组成图。实验结果表明:313.15 K下,此四元体系相图包括两个共饱和点,六条单变曲线以及五个单盐结晶区域(分别为NaNO3,Na2SO4,Na2CO3 H2O,Bur(Na2CO3·2Na2SO4),Da(NaNO3·Na2SO4·H2O)),其中Bur的结晶区域最大,最容易从混合溶液中结晶析出。实验中的物理性质(黏度、密度、折射率)随J(Na2SO4)的变化呈现相似性规律。该体系中存在复盐碱芒硝Bur(Na2CO3·2Na2SO4)、钠硝矾Da(NaNO3·Na2SO4·H2O),结晶水合物(Na2CO3·H2O),没有固溶体存在,故该体系是一个复杂的共饱和型。实验所获数据和结论对煤化工过程产生的高盐废水结晶析盐工艺开发及实现资源梯级综合利用具有重要意义。

An experimental study on phase equilibria of the system Na^+//SO4^2-,CO3^2-,NO3^--H2O at 313.15K was done by the method of isothermal solution saturation. The solubility and physical properties (ρ,η, nD) of the equilibrium quaternary system were measured, and the corresponding phase diagram, water diagram and physical property (ρ,η, nD) diagram were obtained based on the data measured. The results show that: the phase diagram of Na^+//SO4^2-,CO3^2-, NO3^--H2O at 313.15 K consists of two invariant points, six univariant curves, and five crystallization regions which are NaNO3, Na2SO4, Na2CO3 · H2O, Bur(Na2CO3 · 2Na2SO4), and Da(NaNO3 · Na2SO4 · H2O), respectively. The Bur crystallization field occupies the largest part, which indicates it is easier to crystallize in the mixing solution. All the physical properties (ρ,η, nD) change regularly with J(Na2SO4) composition. Bur(Na2CO3 · 2Na2SO4), Da(NaNO3 · Na2SO4 ·H2O) and crystalline hydrate (Na2CO3 ·H2O) are proven to co-exist in the quaternary system, whereas no solid solution is found in the temperature range investigated, which means the reciprocal quaternary system is a complex eutectic type. The data and conclusions obtained from the experiment are of great significance for the development of crystallization salt separation process of high salt wastewater produced by coal chemical process and the realization of comprehensive utilization of resources.