Selective extraction of scandium from other rare earth elements using a hydrophobic protic ionic liquid composed of decanoic acid and TOA

Rare earth elements (REEs) are increasingly being used in advanced materials, but their extraction remains a major challenge. This is primarily due to their nearly identical ionic radii and similarity in chemical and physical properties. Therefore, this study aims to explore the use of a hydrophobic protic ionic liquid (PIL) composed of decanoic acid and trioctylamine (TOA) to selectively extract scandium (Sc) from other REEs using acid or salt as the extraction medium. In the acidic medium, the extraction efficiency of all tested REEs was inversely proportional to the acid concentration. Meanwhile, the extraction percentage of Sc was significantly higher than that of other REEs in the HCl medium, showing that the condition could be used to selectively extract Sc. The results showed that HNO3 medium led to a higher overall extraction percentage but lower selectivity among REEs. The extraction efficiency of REEs in salt media was directly proportional to salt concentration. At higher salt concentrations, the extraction efficiencies became similar, suggesting that the condition could be used for collective extraction. At an organic-to-aqueous phase volume ratio of 0.7, Sc was fully extracted, and dysprosium extraction remained below 17%, offering a promising approach for the selective extraction of Sc from advanced materials and addressing a key challenge in REE separation.