A novel ammonium ionic liquid based extraction strategy for separating scandium from yttrium and lanthanides

Ionic liquid (IL)-based extraction is a promising high-efficiency and environmentally benign separation technology. Imidazolium ILs lose their cations or anions to aqueous phase during extraction, the release lead to water pollution. To develop sustainable IL-based extraction system, we firstly investigate quaternary ammonium nitrate IL-based extraction strategy. Alkylated phosphine oxides (Cyanex925) in tricaprylmethylammonium nitrate ([A336][NO3]) are studied for separating Sc from Y and lanthanides. Distribution ratio and separation factor of the Cyanex925–[A336][NO3] system for Sc3+ are by far larger than those achieved using Cyanex925–[C8mim][PF6] system. The stability and solvating mechanism of Cyanex925–[A336][NO3] extraction system can avoid release of [A336][NO3] to aqueous phase. The novel quaternary ammonium nitrate IL-based extraction system is an efficient and sustainable separation strategy.

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► The solubility of [A336][NO3] is low in acidic aqueous phase.
► Extractability and selectivity of Cyanex925 in [A336][NO3] for Sc3+ are large.
► Solvating mechanism of [A336][NO3] system avoid the loss of IL.
► Cyanex925–[A336][NO3] system maintains high extractability after five cycles.