Leaching Systems of Wolframite and Scheelite: A Thermodynamic Approach

A linear correlation between free energy and enthalpy for crystalline and soluble oxocompounds based in the Sverjensky–Molling equation is used to calculate the Gibbs free energies of formation of MnWO₄ (?1172.48 ± 12.76 kJ mol^?1), H₂WO₄ (?1006.91 ± 10.36 kJ mol^?1), and Na₂WO₄ (?1455.39 ± 12.81 kJ mol^?1). Using these data with the known thermodynamic data, the equilibrium constants for reactions of leaching of scheelite and wolframite in acidic and basic media were determined. The results show that the acid route based in relatively cheap inorganic acids is desirable for scheelite digestion, despite the diffusion problems concerned with tungstic acid developed on the solid particles. Meanwhile, wolframite may be operated under favorable thermodynamics conditions by alkaline and acid processes.