The speciation of Nb in silicate and carbonate melts

The speciation of Nb in silicate and carbonate glasses will be investigated using valence to core X-ray emission spectroscopy (V2C XES). Nb is classed as a “critical metal” due to its importance for green energy solutions and electronic devices but insecure geopolitical supply. Globally, major Nb resources are associated with rocks that crystallised from a carbonate melt, called carbonatites, while some of the largest European Nb deposits are associated with unusual, highly alkaline, silicate melts. Currently the reason(s) why Nb is concentrated in these rocks are unknown. The ligands, O (as O2-, OH-, and CO32-), F and Cl, that complex with Nb exert a primary control on its geochemical behaviour. We have synthesised a series of Nb-bearing silicate and carbonate glasses that have systematically varying F contents. We will use V2C XES to distinguish between either predominately O or F coordination. This will significantly improve our ability to model the geochemical behaviour of Nb.