Separation and Purification of Ta and Nb from Ammonium Bifluoride Leachates Using Methyl Isobuthyl Ketone, 2-Octanol, and Aliquat® 336

Abstract

Results from purification and separation of Ta and Nb from bifluoride-based leachates aiming to produce high-purity Ta and Nb oxides are reported. The leachates have been generated through ammonium bifluoride (NH₄F⋅HF) fluorination (5/1 ratio to ore), followed by sulfuric acid (1 M) leaching of the fluorinated product. Under these conditions, leachate concentration in Nb was 4.2 g/L, while Ta varied between 15 and 17 g/L. Contact time, organic/aqueous (O/A) ratio, and sulfuric acid concentration of the aqueous phase were investigated on their influence on the level of Ta/Nb extraction and separation efficiencies of methyl isobuthyl ketone (MIBK), 2-octanol (OCL), and Aliquat®336 used as solvent extractants. Results show that Ta and Nb could be successfully separated from ammonium bifluoride using the three studied extractants. In the case of MIBK and OCL (100% concentration), the optimum conditions for Ta/Nb separation were found as follows: leachate acidity—3 M, contact time—15 min, and O/A ratio—1. Separation factors of Ta against Nb (SF_Ta/Nb) of about 280 (MIBK) and 51 (OCL) were accordingly reached. When 3% Aliquat®336 was used, the highest Ta vs. Nb separation factor (SF_Ta/Nb = 180) was obtained at O/A ratio of 1 employing 2-min contact time without acidity adjustment. The separation performance of the three extractants could be ranked in the following order: MIBK > Aliquat®336 > OCL. MIBK could nevertheless be substituted at industrial scale by Aliquat®336 due to its known process relevant advantages (higher flash point (132 °C) and lower solubility < 0.5%). After stripping of the loaded Aliquat®336, Ta and Nb were precipitated and precipitates calcinated. Ta and Nb oxide powders with purity around 93% were, thus, obtained and their morphology examined by SEM.

Graphical Abstract