Partitioning and Hydrolysis of Nb and Ta and Their Implications with Regard to Mineralization

Partitioning and hydrolysis of Nb and Ta and their implications with regard to mineralization

K₂NbOF₅ · H₂O and K₂TaF₇ were prepared through melting Nb₂O₅ and Ta₂O₅ respectively with KHF₂ · 2H₂O, followed by recrystallizing. The hydrolysis properties of K₂NbOF₅ and K₂TaF₇ were determined again by using a rapidly quench vessel. As temperature (from 250 to 550 °C) and pressure (from 500 to 1500 bars) increase, the degree of hydrolysis of both K₂NbOF₅ and K₂TaF₇ will increase. Nb- and Ta-fluorine complex compounds are instable in supercritical aqueous fluids. The degree of hydrolysis of both K₂NbOF₅ and K₂TaF₇ decreases with increasing concentration of HF, independent of the concentration of NaF. The partition coefficients of Nb and Ta between granitic melt and fluid phase are less than 0.15, i.e., most of Nb and Ta are left in granitic melt. The partition coefficient of Ta is more dependent on the concentration of HF than that of Nb. The significance of hydrolysis in Nb- and Ta- mineralization is also discussed in the present paper.