An excellent extraction selectivity towards Sc over other REEs in 4 mol/L HCl solution was achieved with the separation factor βSc/REEs over 8000 by 2-ethylhexyl phosphoric acid mono 2-ethylhexyl ester (HEHEHP) and the extraction equilibrium can be obtained within 20 min. The extracted Sc can be stripped using 5 mol/L NaOH solution as eluent at 363 K with the stripping rate of 92.1% obtained. The extraction mechanism was clearly elucidated by slope analysis, saturation extraction, IR, and NMR analysis. It was revealed that the extraction of Sc in 4 mol/L HCl solution is still dominated by cation exchange process between P—O—H and Sc, and coordination process between P=O and Sc, with 6 molecules of extractant as dimer participating in the process. Finally, a flowsheet for the recovery of Sc from ion-adsorption rare earth elements (REEs) concentrate was proposed and proved in lab-scale experiment.