Solvent Extraction of Tantalum and Niobium from Oxalic Leachates: A Novel Technique of Colombo-Tantalite Ores Processing

Tantalum (Ta) and niobium (Nb) are two strategic metals which are extensively used in high-tech industries, such as microelectronics, defense, aerospace, manufacturing of high-strength low- alloy (HSLA) steel, etc. Current and future demand for these two metals will grow in parallel to high-tech equipment need expands. However, their extractive metallurgy remains a major challenge owing to economic and environmental constraints.
Apart the well-known hydrofluoric acid media, alkaline media has attracted reasonable attention in processing of low-grade Ta-Nb bearing ores, but it is limited in terms of Ta and Nb purification. In our previous studies, we proposed a novel method for coltan ore processing based on alkaline roasting, water leaching, precipitation and oxalic leaching of Ta and Nb with the aim to deliver a suitable leachate for downstream treatment by solvent extraction.
The current contribution reports results from the purification steps of Ta and Nb from an oxalic leachate containing about 11 g/L Nb and 2 g/L Ta. Solvent extraction was implemented using an Aliquat® 336-based extractant diluted in toluene and modified with 2% isodecanol. The used extractant is characterized by a higher flash point (132°C), compared to the conventional methyl isobuthyl ketone (14°C) which is very hazardous. The studied parameters have included Aliquat® 336 concentration, contact time, pH, extraction temperature and O/A volume ratio. At their optimum found values, over 98% of Ta and Nb were extracted and purified from impurities and distribution coefficients of more than 300-Ta and 80-Nb were reached. Furthermore, selective stripping was carried out to separate the two metals, enabling to produce high-grade oxides.