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

Abstract

Please cite this article as: Timofeev, A., Migdisov, Art.A., Williams-Jones, A.E., An experimental study of the solubility and speciation of niobium in fluoride-bearing aqueous solutions at elevated temperature, Geochimica et Cosmochimica Acta (2015), doi: http://dx. AbstractThe solubility of Nb 2 O 5 and the speciation of niobium in HF-bearing aqueous solutions have been determined at temperatures of 150, 200, and 250 °C and saturated water pressure. At a pH of ~2 and at low HF concentration, niobium is transported primarily as the species Nb(OH) 4 + and at high HF concentration, as the species NbF 2 (OH) 3°. Equilibrium constants for the formation of Nb(OH) 4 + range from -11.23 ± 0.26 to -10.86 ± 0.24 and for the formation of NbF 2 (OH) 3° from -3.84 ± 0.20 to -5.08 ± 0.42, at 150 and 250 °C.The results of this study show that the solubility of Nb 2 O 5 (solid) in aqueous fluids increases with increasing HF concentration, but is not strongly affected by temperature. The influence of pH is variable;at low pH and HF concentration, a decrease in pH increases the solubility of Nb 2 O 5 (solid). At higher pH the reverse may be true. Modeling of the transport and deposition of niobium suggests that simple mixing with a brine is not an effective method for removing niobium from solution. By contrast, interaction of an acidic fluid with carbonate rock results in a rapid reduction of capacity of the fluid to mobilize niobium.

Geochemical Signature of Magmatic-Hydrothermal Fluids Exsolved from the Beauvoir Rare-Metal Granite (Massif Central, France): Insights from LA-ICPMS Analysis of Primary Fluid Inclusions

“…Secondly, the crystallization of massive topazite and the partial dissolution of the quartz veins in the La Bosse stockwork imply that the magmatic fluid was F-and Al-rich and undersaturated relatively to SiO 2 and has slightly interacted with the enclosing rocks. Finally, the relatively high contents of Nb and Ta in the L1 fluid are also consistent with a high concentration of F, which has been shown to increase significantly the solubility of Nb and Ta in hydrothermal solutions [79,80]. This resulted in the precipitation of Nb (and Ta) as columbite-tantalite and wolframoixiolite in microvugs during the topazification of the quartz-ferberite stockwork [42].…”

Hydrothermal metasomatism of a peralkaline granite pegmatite, Khaldzan Buragtag massif, Mongolian Altai; complex evolution of REE-Nb minerals

“…(b) F in the hingganite is below detection and fluorite is absent. (c) Retention of Nb in the system, as aeschynite and to a minor extent in TiO 2 and titanite, is consistent with a low F content in the fluid; the solubility of Nb 2 O 5 (solid) in aqueous fluids increases with increasing HF concentration, as shown experimentally by Timofeev et al (2015).…”

Ti-Nb Mineralization of Late Carbonatites and Role of Fluids in Its Formation: Petyayan-Vara Rare-Earth Carbonatites (Vuoriyarvi Massif, Russia)

“…This preserved niobium in the fluid phase. Moreover, according to recent studies [71], when the high HF content in solution is high, a decrease in temperature could lead to an increase in the solubility of Nb as niobium hydroxyl-fluoride species and its accumulation in the residual fluid. Further migration of this residual fluid to adjacent dolomite carbonatites formed the chain-like pyrochlore mineralization and Nb-rich rims in anatase and brookite from TiO 2 -carbonate veinlets.…”