oa South African Journal of Chemistry - Dissolution and quantification of tantalum-containing compounds : comparison with niobium : research article
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 a basic 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.
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