The overall objective of this project is to provide a scientific basis for safely processing complexant-containing high-level tank wastes for disposal. Our key goals are to identify methods for preparing realistic complexant-containing tank waste simulants, and to use those simulants to determine the relative importance of organic complexants and their breakdown products on the partitioning of important radionuclides. Complexant containing waste simulants are aged by various chemical processes and compared to samples of actual Hanford tank waste. This work will help to identify important aging processes in the tanks and provide the basis for developing successful treatment strategies.