Speciation of radionuclides in colloidal matter of underground waters taken from observation wells in the zone of impact of Lake Karachai

The strength of actinide bonding with colloidal matter of groundwaters from the Lake Karachai contamination area was studied by selective leaching. An α-track analysis showed that the microdistribution of α-emitting radionuclides in the colloidal matter is uniform. Analysis of fission tracks confirms the presence of ²³⁹Pu and ²⁴¹Am in the colloidal material. In the colloidal matter of groundwaters taken from three wells and differing in the chemical composition, radionuclides occur in forms differing in the solubility. U and Np in the colloidal material are associated only with readily soluble and mobile groups of compounds and are not detected in the difficultly soluble residue. Pu and Am, on the contrary, occur in the colloidal material of groundwaters mainly in difficultly soluble forms. Am is bound to a greater extent with surface organometallic complexes. Pu is detected mainly in the fraction of amorphous oxides.