Production of pure tantalum and niobium oxides by hydrometallurgical processing of coltan smelter cake from Tanganyika Province/RD Congo using NH<sub>4</sub>HF<sub>2</sub>-KOH flux system.

Pure tantalum and niobium oxides were produced from the molten cake after mixing ore-NH<sub>4</sub>HF<sub>2</sub>-KOH in a respective mass ratio of 1/4/3. This resulted in solubilization yields of over 95% for Nb and around 92% for Ta in sulfuric acid solution 3 molar. Extraction of tantalum and niobium using octan-2-ol yielded over 95% niobium and 98% tantalum when pH is set at 0.5-1.0 and 1.5-2 respectively. The compounds K<sub>3</sub>NbOF<sub>6</sub>, K<sub>3</sub>NbO<sub>4</sub> and K<sub>2</sub>TaF<sub>7</sub> were identified after melting. While in aqueous solution ionic species such as NbF<sub>6</sub>(OH)<sub>2</sub><sup>3-</sup>, NbF<sub>6</sub><sup>-</sup> and TaF<sub>7</sub><sup>2-</sup> are likely to be identified. Precipitation of tantalum and niobium in NH<sub>4</sub>OH solution (pH=7.50-8.0) as hydrated oxides after stripping with distilled water and crystallization by evaporation identified hydrated oxides such as Ta<sub>2</sub>O<sub>5</sub>.nH<sub>2</sub>O, Nb<sub>2</sub>O<sub>5</sub>.nH<sub>2</sub>O. These two oxides were associated with a small amount of SiO<sub>2</sub>.nH<sub>2</sub>O as an impurity resulting from the extraction and precipitation of tantalum and niobium. SEM-EDS, XRD, TGA-DTG and FTIR analyses identified and characterized these compounds.