Fluorination Coupled to Sulfuric-acid Leaching for Efficient Extraction of Ta and Nb from Numbi Coltan Ore (South-Kivu, DRC)

The recent developments in advanced technologies, especially in the field of telecommunications, steel making, aerospace and nuclear energy have strongly reinforced the demand for tantalum (Ta) and niobium (Nb). On the other hand, the extractive metallurgy of Ta-Nb remains particular challenging due to the harmful environmental effects associated with the use of hydrofluoric acid (HF) being the principal leaching agent for Ta-Nb bearing ores. Results in direction of development of a hydrometallurgical alternative to the HF-process, consisting of ore pre-treatment with ammonium bifluoride (ABF) followed by sulfuric acid leaching are presented. The most influential process parameters on Ta and Nb recoveries during the fluorination and leaching were identified using a Taguchi L9 orthogonal array experimental set-up. Analysis of variance (ANOVA) was realized to highlight the order of significance of the studied process parameters. Obtained results suggest that more than 90% of Ta and Nb could be leached when ore granulometric fraction, ratio of ABF to ore, fluorination temperature, and sulfuric acid concentration are kept at their optimal values. Fluorination temperature was factor with the most pronounced influence on leaching both Ta and Nb. The resulting leachates are suitable for downstream separation and purification of Ta and Nb.