Thermodynamic Modeling of R₂O–V₂O₅ Systems (R = Li, Na, K, Rb, and Cs) With Key Experimental Study and Its Applications

Abstract

Key phase diagram studies of Li₂O–V₂O₅, K₂O–V₂O₅, and Rb₂O–V₂O₅ systems were conducted using X-ray diffraction and differential thermal analysis within Pt crucibles. The XRD results confirmed the existence of stoichiometric phase Li₄V₃₄O₈₇ in the Li₂O–V₂O₅ system. In the K₂O–V₂O₅ system, the melting temperatures of K₂V₈O₂₁ and KVO₃ were experimentally determined to be 532.4°C and 516.5°C, respectively. The eutectic reaction between liquid, Rb₃V₅O₁₄, and RbVO₃ in the Rb₂O–V₂O₅ system was identified at 496°C with a composition of 42 mol% Rb₂O. The modified quasichemical model (MQM), which accounts for the short-range ordering of the second-nearest neighbors of cations in molten oxide solutions, was employed to describe the liquid phase, and compound energy formalism (CEF) was applied to model the Li_1+XV₃O₈ solid solution at elevated temperatures. Thermodynamic modeling of the R₂O–V₂O₅ (R = Li, Na, K, Rb, and Cs) systems was developed using the CALculation of PHAse Diagrams (CALPHAD) methodology. The experimental data across the entire composition range of the R₂O–V₂O₅ systems were successfully reproduced, and thermodynamic properties for all solid and liquid phases within all binary systems were obtained. The developed thermodynamic database was further applied to simulate vanadium extraction processes, with the optimal operation windows.

Keywords

CALPHAD / phase diagram / R₂O–V₂O₅ systems / thermodynamic optimization

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