MgCl2+NaCl+H2O体系相图计算及其在氯化镁重结晶提纯中的应用

利用Pitzer电解质溶液热力学模型,对MgCl2+NaCl+H2O体系部分多温相图进行了模拟。借助获得的多温相图,对含有NaCl杂质的六水氯化镁试剂重结晶提纯中出现的异常现象进行了分析。研究结果表明,重结晶法提纯化学纯试剂的有效性不是绝对的。虽然化学试剂中的杂质含量已经很低,但是是否能够使用重结晶法进一步提纯是由试剂和试剂中所含杂质的类型决定的。对于主要含有NaCl杂质的六水氯化镁试剂,只有当NaCl杂质含量低于一定值时才能够利用一步重结晶取固相的方法进行提纯;高于此值时,利用一步重结晶取固相的方法反而会使产品质量越来越差。当六水氯化镁中杂质含量高于临界值时,想要对其进行提纯,必须采用分步结晶的方法,首先去除先析出的NaCl杂质。

Phase Diagram Simulation of System MgCl2+NaCl+H2O and the Application in Magnesium Chloride Purification by Recrystallization

By using a Pitzer's model,partial polythermal phase diagram of system MgCl2+NaCl+H2O has been simulated.Based on the simulated phase diagram results,the abnormal phenomena during magnesium chloride hexhydrate purification by recrystallization has been revealed and analyzed.The researches showed that the validation of recrystallization in chemical reagent purification is not absolute.Though the content of impurity in most chemical reagent is very low,the kinds of reagent and impurities are still a crucial factor in the recrystallization process.For MgCl2 6H2O chemical reagent in which NaCl is as the major impurity,the recrystallization method is valid only if the content of impurity is lower than a critical value.Otherwise,the purity of the product of recrystallization will be even worse.