Method for extracting and separating light rare earth element

A method for separating a target light rare earth element via solvent extraction from an aqueous solution containing at least two light rare earth elements selected from the group consisting of lanthanum, cerium, praseodymium and neodymium, comprising the steps of

• contacting an organic phase containing an extractant with an aqueous phase which is the aqueous solution containing at least two light rare earth elements in a counter-current flow multistage mixer-settler while adding an alkaline solution thereto, for extracting the target element into the organic phase, the extractant being a dialkyl diglycol amic acid having the general formula (1):
• R′R2NCOCH2OCH2COOH (1)
• wherein R1 and R2 are each independently straight or branched alkyl, at least one being an alkyl group of at least 6 carbon atoms, and
• contacting the organic phase with an acid aqueous solution for back-extracting the target element,
• wherein the amount of alkali in the alkaline solution used in the extracting step and the amount of acid in the acid aqueous solution used in the back-extracting step each are 1.2 to 2.9 equivalents relative to the light rare earth elements in the aqueous phase.