Fission Product Recovery from Waste Solutions by Solvent Extraction

Abstract

Increasing industrial, military, and space requirements for certain fission products places emphasis on new and large-scale methods for their recovery from reactor process waste liquors. With recent developments of new organic extractants for these fission products, solvent extraction offers a versatile alternate technology to ion-exchange, precipitation, and crystallization technologies heretofore used for small-scale recoveries. A process flowsheet has been developed for recovery of strontium and mixed rare earths from adjusted Purex 1WW using di(2-ethylhexyl)phosphoric acid (D2EHPA). After addition of tartrate to complex iron and caustic to adjust the pH to 6, strontium and rare earths are coextracted, then co-stripped with HNO₃ 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 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 has been developed which removes nitric acid, iron sulfate, zirconium-niobium, and ruthenium from waste solutions to furnish a feed liquor more amenable to subsequent fission product recovery processes. The separate recovery of ruthenium, zirconium-niobium, and rare earths may also be possible by amine extraction. A process has been developed for recovery of cesium from alkaline waste solutions using substituted phenols. These compounds are selective extractants for cesium, giving high decontamination from other fission products and sodium. They are readily stripped with dilute HNO₃. Previous studies have also outlined methods for recovering neptunium, plutonium, and technetium with solvents similar to those described here. When appropriately combined, these developments offer a versatile integrated solvent extraction flowsheet for recovery of all important fission products and other components from waste liquors.