[en] Plutonium(VI)-phosphate species in aqueous solution, at pH < 2.4, formed two species: PuO₂H₂PO₄⁺ (characterized by an 835 nm absorption band) and the solid phase PuO₂(H₂PO₄)₂. The stability constant β for the PuO₂H₂PO₄⁺ species was determined to be log β = 2.1 ± 0.1 (ionic strength = 0.6--0.9 M) and log β^T = 2.6 ± 0.15 (zero ionic strength). Four Pu(VI)-phosphate species (absorption bands at 842, 846, 857, and 866 nm) formed at pH = 2.4 to 12.2 and are characterized by polynuclear behavior, the formation of precipitates, and colloidal properties. The 842 and 846 nm species are believed to be [PuO₂(HPO₄)_m]_n and [PuO₂(NaPO₄)_m]_n. The 857 and 866 nm species area as yet unidentified. The speciation of plutonium with phosphate is of interest to radionuclide migration studies because phosphate is present in many groundwaters and may be used as an actinide getter in nuclear waste disposal. An actinide getter is a complexing agent that forms insoluble phases with actinides, thereby reducing their migration