“…In this process, several solvents were studied for the extraction of Ta and Nb, namely bis-(2-ethylhexyl) phosphoric acid (DEHP) [10], trioctyl-phosphine oxide (TOPO) [11], dibenzo-18-crown-6 (B18C6) [12], tri-n-butyl phosphate (TBP) [13], ketones such as diisopropyl ketone, diisopropyl butyl ketone, n-butyl ethyl ketone [14,15], methyl isobutyl ketone (MIBK) [16] and cyclohexanone [13], amides such as dimethyl heptyl acetamide [17] and bis-2-ethylhexylacetamide [18], secondary and tertiary amines [19,20] such as tri-n-octylamine [21], Alamine™ 336 and tri-n-decylamine, quaternary ammonium salts [10], such as tri-n-octylmethylammonium, tri-n-octylpropylammonium and ethyl benzyl dimethylammonium chlorides, tetrahexylammonium iodide, tri-n-octylmethylammonium hydroxide, bis-tri-sulfate n-octylmethylammonium, bistetrahexylammonium sulfate and tri-n-octylmethylammonium nitrate, as well as long chain alcohols, such as 1-octanol, 2-octanol [9,15] and isoamyl alcohol [5,17]. Among these solvents, only MIBK, TBP, cyclohexanone and 2-octanol are used industrially.…”