Synergistic Extraction of Europium (III) using Di-n-Butylsulfoxide and Picrolonic Acid

Aim and Objective: Europium (Eu(III)) is a rare-earth metal, the softest, least dense, and most volatile member of lanthanides. It is greatly applied in the control rods of nuclear reactors. Although various extraction methods of Eu(III) have been reported, we present a novel mixture of easily available extractants in optimized experimental conditions to extract it efficiently, quickly, and cost-effectively. Materials and Methods: Physical-chemical conditions (e.g., pH, equilibration time, temperature, europium concentration, extractants concentration, presence of specific metal ions) were optimized. The extractants, picrolonic acid (HPA) and di-n-butylsulfoxide (DBSO), were thoroughly mixed at equal concentration in chloroform. Standard Eu(III) solution was used for determining the method’s accuracy. Reagent blank was prepared under identical conditions but without metal ions. Using the metallochromic dye arsenazo III as the blank, the absorbance of Eu(III) was measured spectrophotometrically at 651 nm. The distribution ratio (i.e., Eu(III) concentration in the aqueous phase before and after extraction) defined the extraction yield. Results: HPA/DBSO mixture (0.01 M) had a synergistic effect on Eu(III) extraction (1.19×10^-5 mole/dm³), achieving a maximum yield (≥ 99%) at pH 2, during 5 minutes equilibration at room temperature. Eu(III) extraction was reduced depending on the nature but not on the metal ions concentration. Extractants could be recycled four times without consequent degradation. Deionized water (dH2O) was the best strippant besides its availability and low-cost. The composition of the extracted adduct was defined as Eu(PA)3.2DBSO. Conclusion: This alternative method was found to be stable, simple, rapid, cost-effective, reliable, accurate and sensitive. It could be used for Eu(III) extraction and refining on a pilot plant scale.