To effectively manage the recycle and disposal of the fission byproducts, the chemistry of the most challenging elements must be addressed in two dif­ferent stages, during the recycling process (generally solution chemistry) and wastes produced from the recycling process (generally solid-state chemistry). Some nuclear and radiological features have been discussed in the previous section. In this section, the emphasis will be on discussing the essential features of the solution phase and solid-state chemistry of these elements, starting with the lightest, proceeding to the heaviest and empha­sizing the aqueous chemistry that is of the greatest significance. The discus­sions of the chemistry start from the lightest elements to the heaviest.