Toward Redox- and Photoredox-Based Niobium/Tantalum Separations

Niobium
(Nb) and tantalum (Ta) present a challenging
chemical separation
due to their similar reactivities. Modern Nb/Ta separations employ
hydrofluoric acid, relying on speciation differences between the two
metals in fluoride-containing media. The environmental, health and
safety, and economic implications of hydrofluoric acid use present
an opportunity for the development of alternative separation techniques.
In this study, we introduce two fluoride-free approaches for NbVCl5/TaVCl5 differentiation.
Our electrochemical-based technique leverages the more accessible
NbV/IV redox couple and results in a selective precipitation,
yielding a separation factor, SNb/Ta =
13.1 ± 2.9. This result represents a considerable improvement
compared to previously reported redox-driven methods (SNb/Ta = 6 ± 2). In addition, we present a photochemical
method that selectively produces NbIVCl4 solids
from a NbV/TaVCl5 mixture, achieving
a separation factor of SNb/Ta = 16.1 ±
4.0 by a photoredox-driven separation. This technique similarly manifests
due to the orbital energy differences between NbV and TaV, albeit in the excited state. Our findings not only highlight
the electronic structure differences between Nb and Ta but also indicate
new prospective, fluoride-free Nb/Ta separation avenues.