Thermodynamic investigation of compounds in the MnO-V2O5 system and their applications

MnV 2 O 6 and Mn 2 V 2 O 7 are essential compounds in the manganese salt roasting process for extracting vanadium and serve as excellent battery materials. Determining their thermodynamic properties is of significant theoretical and practical importance. In this study, MnV 2 O 6 and Mn 2 V 2 O 7 were synthesized through solid-state synthesis under a nitrogen atmosphere, and their crystal structures were analyzed using X-ray powder diffraction. The heat capacity of MnV 2 O 6 and Mn 2 V 2 O 7 were measured using relaxation calorimetry over the temperature range of 2–300 K. The entropy at 298.15 K, including magnetic contributions, was calculated as 178.99 ± 5.35 J K -1 ·mol -1 for MnV 2 O 6 and Mn 2 V 2 O 7 for 258.93 ± 6.47 J K -1 ·mol -1 . The standard molar enthalpies of formation were determined using high-temperature solution calorimetry in a molten lead borate solvent, yielding -1997.09 ± 23.97 for MnV 2 O 6 and -2427.71 ± 29.12 kJ mol -1 for Mn 2 V 2 O 7 from their element references. Based on these reliable experimental data, other thermodynamic properties, including enthalpy changes, entropy, and Gibbs free energy, were calculated. Finally, thermodynamic simulations were conducted to analyze phase evolution during the manganese salt roasting process and to evaluate the water solubility of MnV 2 O 6 and Mn 2 V 2 O 7 .