Investigation of the multitemperature stable phase equilibria of alkali tetraborates and bromides and molecular thermodynamic modeling based on DFT

• Published in: Journal of molecular liquids 2024-08, Vol.408, p.125309, Article 125309
• Main Authors: Guo, Xiao-Feng, Sang, Shi-Hua, Wang, Ling-Xuan, Luo, Wen-Feng, Yang, Rong, Cui, Lin-Xuan
• Format: Article
• Language: English
• Subjects: Alkali tetraborate; Brines; Bromide; DFT model; Phase equilibrium; Water-salt system
• ISSN: 0167-7322; 1873-3166
• DOI: 10.1016/j.molliq.2024.125309

•Investigated phase equilibria of alkali tetraborate and bromide in brines.•Constructed phase diagram and density-composition diagram based on experimental data.•Established a molecular model based on DFT to predict the phase equilibria.•Considered the primary forms of polyborate ions in solution.•An important reference for the separation of alkali tetraborate and bromide. The multitemperature stable phase equilibria of alkali tetraborate and bromide were investigated by isothermal dissolution equilibrium method. Based on the experimental data, the phase diagrams and the density-composition diagrams of the ternary systems were drawn respectively. The results demonstrate that the phase diagrams of alkali tetraborate and bromide ternary systems with water as solvent at 273.2 K, 288.2 K and 308.2 K consist of one invariant point, two univariate solubility curves and two crystallization fields. The density at the invariant points is greater than that at the adjacent points. Additionally, based on density functional theory (DFT), a molecular model of phase equilibria of alkali tetraborate and bromide was creatively established to predict the phase equilibrium solubilities of the ternary systems. Based on results of Raman spectra identification of borate ions in the ternary mixed solutions, the primary forms of borate ions in solution, namely B(OH)3, B(OH)4−, B3O3(OH)4− and B4O5(OH)42− were comprehensively considered in this work. By comparing the experimental data of these ternary systems with the calculated results of the DFT model, it is found that the DFT model can describe the solid–liquid equilibria of the ternary systems well, and has high accuracy. The investigation of the multitemperature stable phase equilibria of alkali tetraborate and bromide can provide thermodynamic data for separation of alkali tetraborates and bromides in brines.