Separation of Niobium and Tantalum by Liquid Extraction

Abstract

Niobium, also known as columbium, is one of the new industrial metals likely to play an important role in industrial processing in the near future. Its high melting point (4376°F.) and low cross section for neutron absorption (1.1 barns) make it of special interest to the Atomic Energy Commission. Since tantalum, which invariably accompanies niobium in its ores, has a somewhat higher cross section for neutron absorption (21 barns) there is considerable interest in developing an industrial process for producing tantalum-free niobium. Tantalum itself is a valuable metal because of its high melting point (5160°F.

Tantalum, easy as Pi: understanding differences in metal–imido bonding towards improving Ta/Nb separations

“…This new Ta/Nb separations procedure, although squarely in the fundamental scientific space, 5,9–12 represents a notable model system from which valuable chemical insights can be gained. The observed differences in metal–imido reactivity/stability between 1-Ta and 1-Nb is reminiscent of the industrial process wherein Nb(O)F 5 2− is a stable entity in solution, while the analogous Ta complex is not observed under identical conditions.…”

“…8 This process was replaced in the 1960s with the Ames Laboratory process whereby TaF 6 − is extracted from dilute HF solutions of Nb(O)F 5 2− using organic solvents such as methyl isobutyl ketone (MIBK), octanol, or cyclohexanone. 9,10 Today, the primary methods for Ta/Nb separation are derived from this process. 9–12 A drawback of these methods is the need for large quantities of HF.…”

“…9,10 Today, the primary methods for Ta/Nb separation are derived from this process. 9–12 A drawback of these methods is the need for large quantities of HF. While the use of HF allows for good separation efficiencies and high concentrations of metal ions, the use of this toxic and corrosive reagent is nonideal, and ultimately leads to caustic and environmentally damaging waste streams.…”

Toward Redox- and Photoredox-Based Niobium/Tantalum Separations

“…Solvent extraction on such mixtures is used to achieve separation, with S Nb/Ta > 3500. 11 This process was initially discovered in the mid-1950s, refined throughout the 1960s, 12,13 and is the basis for most industrial Nb/Ta separation processes in the modern era. 9,10 Alternative separation techniques for Nb/Ta fluorides include selective precipitation, fractional distillation, ion-exchange chromatography, and liquid membrane separation.…”

“…21 There are also toxicity and safety issues associated with the other inputs required for Nb/Ta separation, such as the use of gaseous ammonia, and solvent-intensive practices such as the methyl isobutyl ketone (MBIK)/HF solvent extraction. 11 The search for nonfluoride methods to separate Nb/Ta has stimulated fundamental, coordination-chemistry-based research toward new methods. Nete and colleagues described a solution-based, fluoride-free chromatographic separation, achieving S Nb/Ta = 9.5−11.5, though this approach requires large volumes of solvent.…”