Use of macrocycles in nuclear-waste cleanup: A realworld application of a calixcrown in cesium separation technology

Abstract

Crown ethers and more recently calixarenes have long been thought to have potential application in the separation of the fission products 137Cs and 90Sr from nuclear waste [1-8]. Through the 1980s, however, practical extraction systems proved elusive. Although much research toward this end had demonstrated a wealth of creative chemistry, fundamental problems related to insufficient extractive strength and selectivity and lack of an efficient means to reverse the extraction stood as barriers to progress. In this review, a solution to the problem of extracting cesium from alkaline nuclear waste will be presented based on calixcrown chemistry originally reported by European investigators starting in 1994 [9-16]. This chemistry was extended and developed toward the specific technology now called the Caustic-Side Solvent Extraction (CSSX) process [17,18] for the separation of cesium from the legacy highlevel wastes stored in underground tanks at U.S. Department of Energy (USDOE) sites [19-21]. The technology has been designed and successfully demonstrated for nearfuture application at the Savannah River Site (SRS) [22-24], but because of the similarity in waste compositions, it is expected that the CSSX process stands as a wellsuited candidate for application to Hanford wastes [25-27] as well. The science background and technology development pertaining to the CSSX process have been described previously in various publications [28-48] and open-literature reports (not all of which are cited here) [48-61]. Thus, in this contribution, we will describe the overall technology itself, both in terms of the underlying chemistry and the engineering that makes the use of CSSX practical. As such, this article is intended to serve as an example of how macrocyclic chemistry can be adapted for an industrial use to meet the demanding requirements of real-world systems. Below, the CSSX process is introduced via a brief historical summary of its development, followed by a description of solvent extraction as applied to nuclear problems and a description of the chemistry and engineering of CSSX. © 2005 Springer. Printed in the Netherlands.