RECOVERY OF FISSION PRODUCTS FROM WASTE SOLUTIONS BY SOLVENT EXTRACTION

Abstract

Increasing industrial, military, and space requirements for certain fission products place emphasis on large-scale methods for their recovery from waste liquors produced by the fuel recovery processes. With development of organic extractants for separating and recovering these fission products, solvent extraction offers a versatile alternative to ion-exchange, precipitation, and crystallization procedures heretofore used for small-scale recoveries. A process flowsheet was developed for the recovery of strontium and mixed rare earths from adjusted Purex 1WW solution by the use of di(2-ethylhexyl)phosphoric acid (D2EHPA). After adding tartrate t complex the iron and caustic to adjust the pH to 6, strontium and rare earths are co-extracted and then co-stripped with nitric acid in the first cycle. In additional D2EHPA extraction cycles, they are isolated as concentrated fractions. The mixed rare earths from this process can be treated by tributyl phosphate (TBP) extraction to separate the individual rare earth elements of which promethium and cerium are of greatest interest. Zirconium--niobium also may be recovered with D2EHPA from acidic waste liquors. An amine pretreatment extraction process was developed for removing nitric acid, iron sulfate, zirconium-- niobium, and ruthenium from waste solutions to furnish a feed liquor more amenable to subsequent processes for recovering fission products. The separate recovery of ruthenium, zirconium-- niobium, and rare earths may also be possible by amine extraction. A process based on the use of substituted phenols was developed for recovering cesium from alkaline waste solutions. These compounds are selective extractants for cesium, giving high decontamination from other fission products and sodium, and they are readily stripped with dilute nitric acid. Previous studies also outlined methods for recovering neptunium, plutonium, and technetium with solvents similar to those described. When appropriately cornbined, these developments offer a versatile integrated solvent extraction flowsheet for the recovery of all important fission products and other components from waste liquors. (auth)