Extraction and separation of samarium and europium by ionic liquid, tri-n-octylmethylammonium bis-(2-ethylhexyl)phosphate ([A336]+ [DEHP]-).

Abstract
Rare-earth elements have presented excellent properties and been utilized in various high-tech applications. Due to a large
increase in samarium and europium demand and their shortage in supply, they are considered critical metals. In this study,
solvent extraction separation of samarium and europium was investigated. Ionic liquid composed of a mixture of two extractants,
namely trioctylmethylammonium chloride (aliquat 336) and bis-(2-ethylhexyl) phosphoric acid, was synthesized and
characterized using FT-IR spectrometry. In addition, the parameters affecting the extraction were investigated. Extractant
concentration and pH of the solution were found to play an important role for the extraction process. The extraction constants
Kd were calculated based on the slope analysis method and found to be 1401.4 and 913.5 for Sm and Eu, respectively.
The temperature had almost no effect on the extraction of the metals within the range 25–55 °C. The effect of nitrate anions
enhances the extraction of both metal ions compared to chloride or sulfate. The best conditions for separation of the metals
were attained at 0.3 mmol/dm3 ionic liquid concentration and phase ratio = 1. The separation factor (αEu/Sm) reached about
12 which is higher than that reported in the literature. A flowsheet for the recovery of the aforementioned metal ions from a
synthetic leach solution resulting from the rare earths cake of Egyptian monazite was also suggested.