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Hydrometallurgical Separation of Niobium and Tantalum: A Fundamental Approach

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Abstract

A mixture of pure Ta2O5 and Nb2O5 was dissolved using two different fluxes, namely NH4F·HF and Na2HPO4/NaH2PO4·H2O. Selective precipitation and ion exchange were used as separation techniques. Selective precipitation using p-phenylediamine in a fluoride matrix resulted in the isolation of 73(3)% tantalum accompanied by 23(5)% niobium. A separation factor of 11(4) was obtained. A single solvent extraction step using methyl-isobutyl ketone at a 4 M H2SO4 yielded excellent Ta and Nb separation in the fluoride solution with 80% of the Ta and only 2% Nb recovered in the organic layer. A two-step extraction recovered 100% Ta at 0.5–4 M H2SO4 with a separation factor of ~2000. A study of the extraction mechanism indicated that the stability of the protonated compounds such as H2TaF7/H2NbOF5 is in the extraction and separation determining steps in this process. A K′ (double de-protonated constant) of approximately 0.2 was calculated for H2TaF7. Only 91.7% Nb and 73.4% Ta were recovered from anion separation using strong Amberlite resin and 96.1% Nb and 52.3% using the weak Dowex Marathon resin from fluoride dissolution.

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Acknowledgements

The authors would like to thank the Research Fund of the University of the Free State, the National Research Foundation (NRF) of South Africa, the South Africa Nuclear Energy Corporation SOC Limited (Necsa) and the New Metals Development Network (NMDN) of the Advanced Metals Initiative (AMI) of the Department of Science and Technology of South Africa (DST) for financial support.

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Authors and Affiliations

  1. Department of Chemistry, University of the Free State, Bloemfontein, 9300, South Africa

    Motlalepula Nete & Walter Purcell

  2. The South African Nuclear Energy Corporation SOC Ltd. (Necsa), P.O. Box 582, Pretoria, 0001, South Africa

    Motlalepula Nete & Johann T. Nel

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  1. Motlalepula Nete
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  2. Walter Purcell
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  3. Johann T. Nel
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Correspondence to Motlalepula Nete.

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Nete, M., Purcell, W. & Nel, J.T. Hydrometallurgical Separation of Niobium and Tantalum: A Fundamental Approach. JOM 68, 556–566 (2016). https://doi.org/10.1007/s11837-015-1711-2

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