RESEARCH ARTICLE

Dissolution and quantification of tantalum-containing compounds: Comparison with niobium

Thomas A. Theron^I; Motlalepula Nete^I; Johan A. Venter^I; Walter Purcell^{I, *}; Johan T. Nel^II

^IDepartment of Chemistry, University of the Free State, Bloemfontein, 9300, South Africa
^IIThe South African Nuclear Energy Corporation Ltd. (Necsa), P.O. Box 582, Pretoria 0001, South Africa

ABSTRACT

Dissolution and quantification of different tantalum compounds was undertaken as part of the development of local processes for the beneficiation and separation of tantalum and niobium from different mineral ores. Dissolution of Ta metal powder, TAN-1 CRM, TaF₅, TaCl₅ and Ta₂O₅ was undertaken with different acid, alkaline fluxes as well as with microwave digestion while quantification was performed using ICP-OES analysis. The success of the different dissolution methods was evaluated on percentage recovery basis, the results discussed and finally compared with those obtained from the corresponding niobium compounds. Quantification results obtained from this study clearly indicated that the percentage recovery of tantalum depended on i) the type of tantalum source and ii) the dissolution process of the different tantalum compounds. Excellent recoveries were obtained with water soluble TaF₅ and TaCl₅ with 101(1) and 100(2) % respectively. Low tantalum recovery was obtained for Ta metal and Ta₂O₅ with microwave digestion in the presence of strong acids (4.1(8) and 9.7(8) %, respectively in the presence of H₂SO₄) and acidic fluxes (1.5(5) % with K₂S₂O₇). Improved recoveries were obtained using basic fluxes for both the metal and the oxide. Fluxing the metal with KOH resulted in a 85(3) % Ta recovery while a maximum of 68(4) % Ta recovery was obtained for Ta₂O₅. Tantalum recoveries of between 75(10) and 90(6) % were obtained for TAN-1 CRM (Ta present as Ta₂O₅) and 95(6) % for Ta₂O₅ with Li₂B₄O₇ as fluxing agent on the removal of the excess of boric acid prior to analysis. A stability study indicated constant recovery in abasic medium while a decrease of up to 10 % in tantalum recovery was obtained in an acidic environment. A comparison with the niobium results obtained in a previous study highlighted the different acid/base properties of the two oxides as well as a possible alternative dissolution/separation step for the two elements from the mineral ore.

Keywords: Dissolution, microwave, fluxes, tantalum, recovery

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Acknowledgements

The authors thank the Research Fund of this University, NECSA and the New Metals Development Network of the Advanced Metals Initiative of the Department of Science and Technology of South Africa for financial support.

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Received 30 May 2011
Revised 19 October 2011
Accepted 24 October 2011

Submitted by invitation to celebrate 2011 the 'International Year of Chemistry'.
* To whom correspondence should be addressed. E-mail: purcellw@ufs.ac.za