Using a series of acidic, alkaline, and complexant solutions, the leaching behavior of U(VI), Am(III) and Sr(II) from synthetic sludges was studied and compared with previously reported results on the behavior of plutonium. Spectroscopic techniques, including EXAFS and NMR, were used to help interpret the leaching behavior. Considerable amounts of U(VI) were removed from the sludges by 3 M NaOH and the leaching of americium by 3 M NaOH was enhanced in the presence of strong oxidants at elevated temperatures. These observations are discussed in terms of actinide speciation in alkaline solutions and expected to have significant impact on the development of the strategies for tank waste sludge washing.