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

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 K_d 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 (α_Eu/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.