T. J. TRANTER, Idaho National Laboratory, USA

Abstract: Solid-phase extraction has become a subject of increased interest for separation applications specific to radioisotopes of the nuclear fuel cycle. The objective of this chapter is to discuss recent advances in the technology with a focus on the separations of minor actinides and lanthanides from streams associated with nuclear fuel reprocessing. The discussion covers various techniques for making solid-phase extraction resins, recent applications, separation flow sheets, column modeling and the potential advantages and disadvantages of the technology.

Key words: solid-phase extraction, extraction chromatography, solvent — impregnated resins, actinide separation, lanthanide separation, nuclear fuel reprocessing, radioactive waste treatment.

13.1 Introduction

The term solid-phase extraction, as used in the context of this chapter, generally refers to macroporous polymers that hold an organic complexing compound or extractant within the pore structure of the polymer. Various literature sources may also refer to this material as extraction chromatog­raphy resins, solvent-loaded resins or solvent-impregnated resins. The mac­roporous polymer supports are roughly spherical beads, appearing much like the resins typical to ion exchange, and may be used in a similar fashion in a column or packed bed configuration. It is often said that solid-phase extraction resins combine the metal selectivity of liquid-liquid solvent extraction with the operational benefits of packed bed ion exchange (Warshawsky, 1981, Cortina et al., 1997). Some of the seminal work in syn­thesizing the first variants of this material was performed by Small (1961), Fritz et al., (1971) and Spevackova et al., (1970) wherein organic polymers were used as solvent supports for analytical separations. Further pioneering work was done by Warshawsky (1974, 1978) and Grinstead et al., (1974) who investigated solvent-impregnated resins for use in hydrometallurgical and effluent treatment applications.

Solid-phase extraction has become an accepted separations technology in pharmaceutical and analytical organic chemistry applications. Over the last twenty years it has also gained wide acceptance in radioanalytical

methods for effecting very clean separations of various radionuclides, espe­cially lanthanides and actinides. The technology of solid-phase extraction was, however, in its infancy when much of the industrial-scale separation schemes were developed for reprocessing nuclear fuel. Thus, it has not been implemented at large scales for this purpose to any significant degree. Nonetheless, liquid solvent extraction techniques for partitioning the trans­actinide (An) and lanthanide (Ln) elements are fairly well understood and it follows that solid supported extractants may offer beneficial improve­ments for select portions of fuel reprocessing flow sheets. The technology has been steadily improved and has reached a level of maturity for analyti­cal and smaller-scale applications. It is therefore the objective of this chapter to discuss the applications and potential merits of solid-phase extraction technology for separating the common actinide and lanthanide isotopes specific to nuclear fuel reprocessing.