The sorption characteristics of the Kara sea bottom sediments were investigated. The sediments were collected during scientific expedition of the R/V Akademik Mstislav Keldysh (Cruise AMK-66). The mineral and fraction composition of sediments was determined. It has been found that 137Cs sorbed predominantly by an ion exchange mechanism because of the clay minerals presence in the sediments. At the same time, 243Am and 90Sr sorbed from seawater by the surface complexation mechanism. The sorption kinetics for 243Am was established: about 20 hours, 137Cs: 2 hours, 90Sr: less than an hour. The sorption isotherms shows Cs and Am in experiments on marine and distilled water are described by the Henry equation. The Sr behavior in deionized water is described by the Langmuir equation, in the case of sea water, by the Freundlich equation.

Complex studies revealed changes in the composition, structure, and properties of bentonite clays from the Taganskoye (Kazakhstan) and Dashkovskoe (Moscow region) deposits due to the thermochemical treatment. The leaching of cations from the interlayer and octahedral positions, protonation of the interlayer and OH-groups, leads to modification of the interlayer and 2:1 layer composition, which in turn contributes to significant changes in properties:-a decrease in the cation exchange capacity due to a decrease in the layer charge and increase in the specific surface due to destruction and partial amorphization. Bentonites from the Dashkovskoye deposit demonstrated higher resistance to thermochemical treatment than the bentonites from the Taganskoye deposit due to the protecting effect of the organic matter. Results of the work showed that even after quite intensive thermochemical treatment (13M HNO3, 90 °C, 5 hours), bentonite clays retain a significant part of the adsorption capacity.