Thermodynamic and Dynamic Modeling of the Boron Species in Aqueous Potassium Borate Solution

[Image: see text] The concentration of B(OH)(3), B(OH)(4)(–), B(3)O(3)(OH)(4)(–), and B(4)O(5)(OH)(4)(2–) in the solution and the solubilities in the system KCl–K(2)SO(4)–K(2)B(4)O(7)–H(2)O and its subsystems were calculated on the basis of the Pitzer model. The mole fraction of the four boron species is mainly affected by m(B) in the solution but less by m(Cl(–)) and m(SO(4)(2–)). m(Cl(–)) and m(SO(4)(2–)) mainly affect the solubility of K(2)B(4)O(5)(OH)(4)·2H(2)O. The calculated solubilities in the system KCl–K(2)B(4)O(7)–H(2)O agree well with the experimental data. The results show that the standard chemical potentials of K(2)B(4)O(5)(OH)(4)·2H(2)O at 298.15 K obtained in this work is reliable. The transformation between the boron species at 298.15 K was also conducted with the density functional theory (DFT) method. The results affirm that the boron species can transform other boron species as the boron concentration in the solution changes.