An experimental study of the solubility and speciation of tantalum in fluoride-bearing aqueous solutions at elevated temperature

The solubility of Ta2O5 (solid) and the speciation of tantalum in HF-bearing aqueous solutions have been determined at temperatures of 100–250 °C and vapour-saturated water pressure.[...] Modelling of Nb and Ta leaching confirmed the preferential mobility of niobium under most conditions expected in natural fluoride-rich hydrothermal systems. This modelling also demonstrated that both niobium and tantalum are rapidly deposited upon removal of fluoride from an acidic brine. As a result of hydrothermal alteration, the Nb/Ta ratios of secondary minerals may increase relative to those of the primary mineral, or remain largely unaffected, depending on the pH of the fluid