Production of pure tantalum and niobium oxides by hydrometallurgical processing of coltan smelter cake from Tanganyika Province/RD Congo using NH₄HF₂-KOH flux system.

Pure tantalum and niobium oxides were produced from the molten cake after mixing ore-NH₄HF₂-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 K₃NbOF₆, K₃NbO₄ and K₂TaF₇ were identified after melting. While in aqueous solution ionic species such as NbF₆(OH)₂³⁻, NbF₆⁻ and TaF₇²⁻ are likely to be identified. Precipitation of tantalum and niobium in NH₄OH solution (pH=7.50-8.0) as hydrated oxides after stripping with distilled water and crystallization by evaporation identified hydrated oxides such as Ta₂O₅.nH₂O, Nb₂O₅.nH₂O. These two oxides were associated with a small amount of SiO₂.nH₂O 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.