Synthesis of niobium oxides powder through combined process of alkali fusion and acid digestion.

Niobium and tantalum oxides are commonly produced through acid digestion of columbite-tantalite (coltan) minerals in hydrofluoric acid followed by solvent extraction, precipitation, and calcination processes. Efforts to improve the purity of the niobium and tantalum oxides have been made by several researchers by implementing alkali fusion followed by water and acid leaching prior to hydrofluoric acid digestion to remove major impurities in coltan such as Al, Sn, Ti, Fe, and Mn. In the present work, synthesis of niobium oxide was performed by combined process between alkali fusion and hydrofluoric acid digestion and characteristic of the synthesized powder was compared with the one obtained by direct acid digestion. The coltan samples were received from a mine area in Nigeria which represent those of high Nb grade (Sample A) and low Nb grade (Sample B). Series of alkali fusion experiments, water leaching and sulfuric acid leaching and their combinations with the HF digestion were carried out to study the effect of the combined process on the purity of Nb2O5 product as well as co-precipitation of Ta in Nb precipitate. The combined process significantly enhanced the grade of Nb2O5 from 81.64% (obtained by direct HF digestion) to 90%. SEM analysis reveals that the niobium oxide powder consists of individual crystals that has a rectangular spike morphology. [ABSTRACT FROM AUTHOR]