Niobium and tantalum in hydrothermal fluids: Thermodynamic description of hydroxide and hydroxofluoride complexes

Available experimental data on the solubility of β -Nb2O5 and β -Ta2O5 in the Nb–O–H–F and Ta–O–H–F systems were critically evaluated, and the thermodynamic properties of hydroxide and hydroxofluoride complexes were estimated in a wide range of temperatures (0–600 °C) and pressures (1–3000 bar). In near neutral pH solutions, the solubility of the oxides is governed by uncharged aqueous hydroxides, Nb(OH)5 and Ta(OH)5, and is rather low even at...