In this study, we examined the sorption behavior of Pu at elevated temperatures in the presence of one relevant mineral, goethite ({alpha}-FeOOH), over a range of concentrations that span solubility-controlled to adsorption-controlled concentrations. We focused on the sorptive behavior of two common forms of Pu: aqueous Pu(IV) and intrinsic Pu(IV) nano-colloids at 25 and 80 C in a dilute pH 8 NaCl/NaHCO{sub 3} solution. The morphology of Pu sorbed to goethite was characterized using transmission electron microscopy (TEM). We examined the relative stability of PuO{sub 2} precipitates, PuO{sub 2} nano-colloids, Pu{sub 4}O{sub 7} surface precipitates, and monomeric sorbed Pu as a function of temperature and over a time scale of months.