Current guidelines for disposing of high-level radioactive wastes stored in underground tanks at the U.S. Department of Energy’s Hanford Site call for vitrifying high-level waste (HLW) in borosilicate glass and burying the glass canisters in a deep geologic repository. Disposition of the low-level waste (LLW) is yet to be determined, but it will likely be immobilized in a glass matrix and disposed of on site. To lower the radiological risk associated with the LLW form, methods are being developed to separate Sr-90 from the bulk waste material so this isotope can be routed to the HLW stream. A solvent extraction method is being investigated to separate Sr-90 from acid-dissolved Hanford tank wastes. Results of experiments with actual tank waste indicate that this method can be used to achieve separation of Sr-90 from the bulk waste components. Greater than 99% of the Sr-90 was removed from an acidic dissolved sludge solution by extraction with di-t-butylcyclohexano-18-crown-6 in 1-octanol (the SREX process). The major sludge components were not extracted.