The fuel is first dissolved in nitric acid at a concentration around 7 M. Solids are removed by filtration to avoid the formation of emulsions, referred to as third phases in the solvent extraction community.
The organic solvent consists of 30% tributyl phosphate (TBP) in a hydrocarbon such as kerosene. Uranyl(VI)  ions are extracted in the organic phase as UO(NO)·2TBP complexes; plutonium is extracted as similar complexes. The heavier actinides, primarily americium and curium, and the fission products remain in the aqueous phase. The nature of uranyl nitrate complexes with trialkyl phosphates has been characterized.
Plutonium is separated from uranium by treating the TBP-kerosene solution with reducing agents to convert the plutonium to its +3 oxidation state, which will pass into the aqueous phase. Typical reducing agents include N,N-diethyl-hydroxylamine, ferrous sulphamate, and hydrazine. Uranium is then stripped from the kerosene solution by back-extraction into nitric acid at a concentration around 0.2 M.