MgB_4O_7-K_2B_4O_7-Na_2B_4O_7-H_2O四元体系288K介稳相平衡研究

Study on metastable equilibria in MgB_4O_7-K_2B_4O_7-Na_2B_4O_7-H_2O quaternary system at 288 K

中国青藏高原的盐湖资源丰富,以富含硼酸盐资源而闻名,且钾、镁储量较大,所以深入开展含硼多组分介稳相平衡的研究,对开发中国盐湖中硼、镁等资源有着重要意义。采用等温蒸发法进行了MgB4O7-K2B4O7-Na2B4O7-H2O四元体系288 K时的介稳相平衡研究,测定了该体系介稳相平衡的溶解度和液相密度。研究发现该四元体系为简单共饱和型,无复盐形成;根据溶解度数据绘制了相图,相图中有一个四元共饱点E和3条单变度曲线E1-E,E2-E,E3-E;平衡固相分别为MgB4O7.9H2O,Na2B4O7.10H2O和K2B4O7.4H2O;由相图可知K2B4O7对Na2B4O7具有盐溶作用。

There are rich salt lake resources in Qinghai - Tibet plateau of China,which were known as the abundant borate resources and large reserves of potassium and magnesium to the world. Therefore, it is very important to carry out deep research on metastable phase equilibrium of boron - containing polycomponent in the exploitation of boron and magnesium resources from salt lakes in China. An experimental study on metastable equilibria at 288 K in the MgB4O7-K2B4O7-Na2B4O7-H2O quaternary system has been done by means of isothermal evaporation method. Furthermore, the solubility and density of the metastable equilibrium solution were determined. The results showed that the system was of simple eutectic type and there＇s no complex salt formed in the MgB4O7 - K2B4O7 - Na2B4O7 - H2O quaternary system at 288 K. The metastable equilibrium phase diagram was plotted by referring to the experimental data. In the phase diagram of the quaternary system,there were one invariant point （E） , three univariant curves （ E1 - E,E2 - E,E3 - E） and three fields of crys- tallization （ MgB4O7-K2B4O7-Na2B4O7-H2O and K2 B4O7 · 4H2O ）. From the diagram, K2 B4O7 had the salting - in effect on Na2B4O7.