Task-Specific Ionic Liquids as Extractants for the Solvent Extraction of Molybdenum(VI) from Aqueous Solution Using Different Commercial Ionic Liquids as Diluents

In this work, the recovery of molybdenum­(VI) (Mo) from aqueous solutions was carried out by solvent extraction (SX) using ammonium and phosphonium-based task-specific ionic liquids (TSILs) as extractants diluted in kerosene and two other hydrophobic room-temperature ionic liquids (RTILs). Four different TSILs were used as extractants: trioctylmethylammonium bis­(2-ethylhexyl) phosphate [TOMA]­[D2EHP]; trioctylmethylammonium benzoate [TOMA]­[BA]; trihexyltetradecylphosphonium bis­(2-ethylhexyl) phosphate [P<sub>6,6,6,14</sub>]­[D2EHP]; and trihexyltetradecylphosphonium benzoate [P<sub>6,6,6,14</sub>]­[BA]. These TSILs were synthesized to assess the effect of the cation and anion on the SX of Mo­(VI). Experimental results indicated that high extraction percentages of Mo­(VI) were obtained with all the synthesized TSILs. Besides that, the best cation was [TOMA]<sup>+</sup> for all the diluents and [BA]<sup>−</sup> was the best anion when kerosene and 1-octyl-3-methylimidazolium bis­(trifluoromethylsulfonyl)­imide, [omim]­[Tf<sub>2</sub>N], were the diluents. Furthermore, the SX process using these ionic liquids followed an anion-exchange mechanism for kerosene and [omim]­[Tf<sub>2</sub>N] as diluents. Finally, the stripping was successfully performed with a solution of ammonium carbonate, and the extent of stripping depended on the selected diluent.