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Why is separating niobium from tantalum difficult?

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niobium processing Four one-millimetre thick samples of niobium metal foil.

Separating niobium from tantalum is difficult primarily due to their great chemical similarity. This resemblance arises because both elements share similar electronic configurations and possess nearly identical ionic radii, a phenomenon caused by the lanthanoid contraction.12

Because of these shared properties, the two elements are closely associated in nature, frequently occurring together in the same mineral ores, such as the columbite–tantalite series. In industrial niobium processing, this chemical likeness necessitates complex separation techniques, typically involving solvent extraction in a liquid-liquid process to isolate the metals from one another.3124