Аннотация:Plutonium(V) in near neutral media exists in the form of the PuO2+ cation, which migrates and exhibits a weak tendency to complex formation and sorption. The conditions of Pu(V) sorption on the surface of mineral particles of diff erent nature and the reduction of Pu(V) to Pu(IV) with the formation of PuO2 excited by the surface are considered. The action of visible light speeds up the process. Mechanisms based on the semiconductorproperties of minerals, disproportionation reactions or reactions with α-radiolysis products cannot be implementedfor various reasons. A mechanism is proposed that includes the formation of a dimer, the so-called excimer, by anexcited Pu(V) ion with an unexcited Pu(V) ion, which is sorbed on the mineral surface and converted into PuO2.A thermodynamic calculation was carried out confirming the possibility of such a reaction. At plutonium concentrationsof 10–18–10–16 M, the behavior of plutonium is mainly affected by interaction with organic substances,microorganisms, photolysis, and reactions with water radiolysis products arising under the action of radiation from isotopes of uranium families and K-40.DOI: 10.1134/S1066362222060029