ANALYTICAL-SCALE SEPARATIONS OF THE LANTHANIDES: A REVIEW OF TECHNIQUES AND FUNDAMENTALS

Abstract

Separations chemistry is at the heart of most analytical procedures to determine the rare earth content of both man-made and naturally occurring materials. Such procedures are widely used in mineral exploration, fundamental geology and geochemistry, material science, and in the nuclear industry. Chromatographic methods that rely on aqueous solutions containing complexing agents sensitive to the lanthanide cationic radius and cation-exchange phase transfer reactions (using a variety of different solid media) have enjoyed the greatest success for these procedures. In this report, we will briefly summarize the most important methods for completing such analyses. We will discuss in some detail the basic aqueous (and two-phase) solution chemistry that accounts for separations that work well and offer explanations for why others are less successful.

ACKNOWLEDGMENT

Work performed under the auspices of the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences under contract number W-31-109-ENG-38

Notes

¹ For separations based on the application of solvent extraction/extraction chromatography with acidic extractants (like HDEHP), trends in K_ex and β_i work in opposition. Aqueous complexants are therefore of limited utility for separation systems in this combination or reagents. For separations based on cation exchange (either using Dowex 50-type resins or dynamic ion exchange resins), the ratio K_ex ^Ln/K_{ex Ln′} increases from Lu-La, i.e. K_ex ^La > K_ex ^Ce > K^Pr _ex.…, which is opposite the trend in aqueous complex stability.