Na^+,K^+//Br^-,SO_4^(2-)-H_2O四元体系323K相平衡研究

A Study on Equilibria of the Quaternary System Na^+,K^+//Br^-,SO_4^(2-)-H_2O at 323 K

采用等温溶解平衡法研究了四元体系Na+,K+//Br-,SO42--H2O在323 K的相平衡关系,测定了该体系323 K的溶解度及平衡液相的密度,绘制了该体系的相图。研究发现:平衡体系存在复盐钾芒硝Na2SO4.3K2SO4的结晶区。其相图由3个共饱和点,7条单变量曲线和5个结晶区组成。相区分别对应NaBr.2H2O、Na2SO4、K2SO4、KBr和Na2SO4.3K2SO4结晶区。其中复盐钾芒硝Na2SO4.3K2SO4,Na2SO4和K2SO4有较大结晶区,而NaBr.2H2O和KBr有较小结晶区。对比了等温条件下四元体系Na+,K+//Cl-,SO42--H2O相平衡结果。实验结果表明溴化物对硫酸盐有较强盐析作用。

An experimental study on equilibria at 323 K in the quaternary system Na＋,K＋//Br-,SO42--H2O was done by isothermal equilibrium method.The equilibrium solubilities and densities of the solution were determined experimentally.Using the experimental data,the equilibrium phase diagrams were plotted,respectively.The experimental results of the equilibria show that the double salt Na2SO4.3K2SO4 forms in the quaternary system Na＋,K＋//Br,SO42--H2O at 323 K.In the phase diagram,the quaternary system at 323 K has three invariant points,seven univariant curves,and five crystallization fields corresponding to NaBr.2H2O,Na2SO4,K2SO4,KBr and Na2SO4.3K2SO4.The double salt Na2SO4.3K2SO4 and sulfates（Na2SO4 and K2SO4） have larger crystallization fields,but bromides（NaBr.2H2O and KBr） have smaller crystallization fields.The experimental results of Na＋,K＋//Cl-,SO42--H2O quaternary system were compared with the quaternary system Na＋,K＋//Br-,SO42--H2O at 323 K.It isalso found that bromide has the salting-out effect on sulfates in the quaternary system Na＋,K＋//Br-,SO42--H2O at323 K.