Optimization of Niobium-Tantalum Recovery from Typical Rwanda and Nigerian Columbite-Tantalite Ores
Niobium and tantalum are transition metals with a refractory character and unique properties that make them highly indispensable to the high-technologies and clean-energy. The metals are normally extracted from minerals of columbite-tantalite series, pyrochlore, and microlite of various deposits. The traditional method used for their extraction and recovery utilizes corrosive acidic media and highly volatile hydrofluoric acid or its mixture with sulfuric acid which blamed to be associated with cost and environmental challenges. To address these challenges, the present study aimed at optimization of Nb and Ta recovery from typical Rwanda and Nigerian columbite-tantalite ores reports mainly the results of characterization of the ore material-samples from Rwanda and their concentrates obtained after rough centrifugal gravity concentration. Further the columbite-tantalite concentrate materials from Rwanda and Nigeria were subjected to the alkali-assisted roasting to open up and convert into soluble species the minerals of Nb and Ta followed by water-based leaching which solubilizes these refractory metals and then extract them via precipitation using guanidine carbonate. The alkali-assisted roasting at optimum conditions resulted in breaks-up and high dissolution of the (Nb, Ta)-bearing minerals, more than 93% and 90% of Nb and Ta were dissolved from the feed respectively. Guanidine carbonate precipitated effectively almost 100% of the total Nb and Ta contained in the pregnant leach solution. The (Nb, Ta)-guanidine precipitates obtained were calcined at 900C for one hour which removed the guanidine and converted the metals into mixed oxides of Nb and Ta. This gives a total recovery between 96-98% and 92-94% for Nb and Ta respectively. The present work demonstrates the possibility of sustainable extraction in the metallurgy of Nb and Ta while the world is shifting toward the clean energy.