Ammonium ion is of the same charge as alkali ions and with similar ionic radius as potassium, rubidium, and cesium ions. Solid solutions are very common between ammonium and alkali salts, which is of great interest for understanding the geology, soil, and environment fate of these elements. In this study, the solid–aqueous equilibrium in the NH₄Cl + RbCl + H₂O and NH₄Cl + CsCl + H₂O systems was determined at 298.15 K. For each system, two incontinuous solid solutions, i.e. (NH₄,Rb)Cl(α) and (Rb,NH₄)Cl(β), or (Cs,NH₄)Cl(α) and (NH₄,Cs)Cl(β), presented, and their composition and structure were studied using Schreinemakers’ wet residues analysis, XRD, and Raman characterization. The equilibrium between these solid solutions and aqueous solutions were well modeled using an integrated solution equilibrium calculator program, in which a Pitzer-Simonson-Clegg model and a subregular model were implemented for describing the nonideality of aqueous phase and solid solution. According to the experimental and thermodynamic modeling results, NH₄Cl can dissolve RbCl and CsCl in the solid state (NH₄,Rb)Cl(α) or (NH₄,Cs)Cl(β) with limited solid solubilities of 0.18 or 0.051 in mole fraction, respectively. RbCl or CsCl can also dissolve NH₄Cl in the solid state (Rb,NH₄)Cl(β) or (Cs,NH₄)Cl(α) with limited solid solubilities of 0.37 and 0.095 in mole fraction, respectively.

中文翻译：

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298.15 K NH4Cl + RbCl + H2O 和 NH4Cl + CsCl + H2O 系统中的固液平衡

铵离子与碱离子具有相同的电荷，并且具有与钾、铷和铯离子相似的离子半径。铵盐和碱金属盐之间的固溶体非常常见，这对于了解这些元素的地质、土壤和环境命运非常重要。在本研究中，NH ₄ Cl + RbCl + H ₂ O 和 NH ₄ Cl + CsCl + H ₂ O 体系中的固水平衡在 298.15 K 下确定。对于每个体系，两个不连续的固溶体，即 (NH ₄ ,Rb)Cl(α)和(Rb,NH ₄ )Cl(β),或(Cs,NH ₄ )Cl(α)和(NH ₄ ,Cs)Cl(β),其组成和结构为使用 Schreinemakers 的湿残留物分析、XRD 和拉曼表征进行研究。使用集成溶液平衡计算器程序对这些固溶体和水溶液之间的平衡进行了很好的建模，其中使用 Pitzer-Simonson-Clegg 模型和次正则模型来描述水相和固溶体的非理想性。根据实验和热力学模拟结果，NH ₄ Cl可以溶解固态(NH ₄ ,Rb)Cl(α)或(NH ₄ ,Cs)Cl(β)中的RbCl和CsCl，其有限固溶度为0.18或0.051分别以摩尔分数表示。 RbCl或CsCl还可以溶解固态NH _{4 Cl(Rb,NH 4} )Cl(β)或(Cs,NH ₄ )Cl(α)，其有限固溶度分别为0.37和0.095摩尔分数。