Abstract:

Based on the traditional experimental method of isothermal evaporation metastable phase diagram of ternary water-salt system, a slight improvement was made. Experimental study was carried out by taking two ternary systems of K⁺(Mg²⁺), Ca²⁺//Cl^--H₂O as examples. The key experimental steps of the new method are: isothermal evaporation starts from the selected unsaturated solution point; as the evaporation process progresses, grasp the moment before the solid precipitates; before the solid precipitates but is about to precipitate, take out the supersaturated liquid phase and measure its solubility; then construct an isothermal evaporation supersaturation phase diagram. During the experimental process, the liquid phase is in a supersaturated state but not in the phase equilibrium, so the rule of phase equilibrium is not obeyed. Thereby, the two-salt co-saturation of the two ternary systems has changed from the point in the stable phase equilibrium diagrams to the two-salt co-saturation line in the supersaturation phase diagrams obtained by the new experimental method proposed in this paper. Therefore, for the phase diagram formed by the new experimental method, it should not be referred to as the metastable phase equilibrium diagram, but can only be referred to as the supersaturated solubility diagram. By combining the stable phase diagram with the supersaturated phase diagram obtained from the new experimental method, the thermodynamic non-equilibrium phase diagram is drawn. And the salt-forming phase region is obtained for the isothermal evaporation process of ternary system, and thus the supersaturation limits for the actual isothermal evaporation process are given. The comparative experiments for the two ternary systems K⁺(Mg²⁺), Ca²⁺//Cl^--H₂O were conducted using the traditional metastable experimental method, which confirm that the random metastable solubility curves obtained by the traditional experimental method always fall within the salt-forming phase region obtained based on the new experimental method.

Key words: dissolution, solubility, solution, supersaturation, salt-forming phase region, water-salt system

摘要：

基于三元水盐体系等温蒸发介稳相图传统实验方法进行改进，以K⁺（Mg²⁺），Ca²⁺//Cl^--H₂O两个三元体系为例开展了实验研究。结果表明，因液相是过饱和状态，三元体系的两盐共饱由稳定相平衡图的一个两盐共饱点，变为了新方法过饱和相图中的一条两盐共饱线。结合稳定相图与新实验方法所得过饱和相图，绘制了热力学非平衡态相关系图，得到了两个三元体系等温蒸发的成盐相区，从而给出了实际等温蒸发过程的过饱和限度。采用传统介稳实验方案进行了对比实验，证实传统实验方法得出的随机的介稳溶解度曲线会处在基于新实验方法得到的成盐相区内。

关键词: 溶解, 溶解性, 溶液, 过饱和, 成盐相区, 水盐体系