Anion-Dependent Extraction of Ln(III) Using Undiluted Methyltrioctylammonium-Based Ionic Liquids as a Green Extractor: Role of Salting Agents and Spectroscopic Insights

Abstract

Ionic liquids derived from methyltrioctylammonium chloride [N₁₈₈₈][Cl]) play a vital role in governing the coordination and separation process. At the same time, the feed phase salting agent may take a crucial stand in evaluating the metal ion extracting power of ILs. To understand the same, we have chosen couple of ILs based on [N₁₈₈₈⁺] ion with anions: nitrate (NO₃⁻), thiocyanate (SCN⁻) and bistrifluoromethanesulfonylimide (NTf₂⁻) in their undiluted conditions for the separation of lanthanides (Ln(III) from the feed solution with europium (III) (Eu(III)) as the representative ion. The order of extraction in these ILs follows with respect to anions as [SCN⁻] > [NO₃⁻] >> [NTf₂⁻] in presence of their respective salting agents. For instance, The % E values were evaluated to be 95%, 60%, and 20% in [N₁₈₈₈][SCN], [N₁₈₈₈][NO₃], and [N₁₈₈₈][NTf₂] with the help of 4 M NH₄SCN, NH₄NO₃, and LiNTf₂ respectively present in the feed phase. The anion essence was explored spectroscopically to support the extraction results by inferring the formation of a mixed anionic complex in IL phase. Effect of temperature on the extraction was persued and Milli-Q water as the stripping agent offers added merit to the system by removing all the loaded Eu(III) within 2 -3 contacts.