This paper describes the application of reverse-burn gasification (the ChemChar process) for the treatment of mixed wastes, which are wastes containing both hazardous organic matter and radionuclides. The specific wastes studied consisted of ion-exchange resins to which were bound radioactive technetium-99m and non-radioactive surrogates for waste radionuclides. It was shown that with reverse-burn gasification the resins could be dewatered and converted to inert char and innocuous gas products with complete retention of the radionuclides. The residual char can be mixed with Portland cement and water to produce a poorly leachable aggregate in concrete. An approximately 20-fold reduction in volume of the original wet resin can be accomplished with a reverse-burn gasification followed by a forward burn to produce a low-volume, poorly leachable slag.