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The purification of niobium from antimony impurity via extraction with tributyl phosphate from solutions of the HF + NH4F mixture has been studied. It has been established that at an HF + NH4F content equal to 7–16 mol/L and an NH4F concentration of 30% in the mixture, Sb extraction hardly changes (70–80% for one stage), and Nb coextraction abruptly decreases to values of less than 0.5%.