Abstract
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 high temperatures (1–9 ppm for Nb and 0.1–0.9 ppm for Ta at 600 °C, 1000 bar). In acid HF bearing solutions, the solubility is governed by Nb(OH)2F3 and Ta(OH)2F3 complexes and increases sharply with increasing HF molality: at mHF = 0.1 mol·kg−1, 600 °C and 1000 bar, the Nb and Ta concentrations reach 80 and 30 ppm respectively. In alkaline fluoride bearing solutions, the HNbO3F− and HTaO3F− - oxyfluoride anions control the solubility of the oxides. The temperature and pressure dependences of the oxides solubility governed by these fluoride complexes are rather weak; therefore, the neutralization of acid fluoride solution and the loss of fluoride ligand during fluid evolution can be the main factors of Nb and Ta deposition.
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call