a chitin-melanin glucan complex, was studied in solutions. It was shown that the degree of coprecipitation (α) of the radionuclides depended on the solution content of polymer. The maximum value of α was at least 80% for metal-ion concentration 250 mg/L and 0.8% melanin. It was hypothesized that UO 2 2+ , Eu 3+ , and Sr 2+ were bound mainly by carboxylic and phenolic groups of melanin. The developed co-precipitation process could be recommended for isolation and concentration of radionuclides from low-salt process solutions and natural media.The practical use of atomic energy created a complicated problem for the ecological safety of the environment and the population residing near nuclear fuel-cycle facilities. This was due to the fact that long-lived radionuclides such as 235 U, 239 Pu, transuranium elements, 137 Cs, 90 Sr, 60 Co, 152,154 Eu, etc. present a potential hazard for hundreds of years. Measures to limit the spread of hazardous substances include not only improvement of waste treatment technology and volume reduction of industrial wastes and releases but also post-radiative and toxicological rehabilitation of people and environmental sites.A trend toward the expanded use of compounds of natural origin focused special attention on melanin polymers, which can act as active binding agents for heavy metals [1,2]. Melanins are high-molecular-weight compounds of irregular phenolic and (or) indolic structure [3]. They are subdivided according to chemical structure into three classes: eu-, pheo-, and allomelanins [4]. Eumelanins include black N-containing compounds that occur in animals and more rarely in plants. Pheomelanins are also characterized by their distinctive color (red, yellow, brown) and the presence in them of not only N but also S. This class of melanins is encountered only in animals. Allomelanins are blackish-brown compounds of higher plants and fungi that typically have a low N content. Highly stable paramagnetic centers, various reactive functional groups, and systems of conjugated double bonds are characteristic of melanin polymers. A lack of systematic information on the structure and physicochemical properties of melanin polymers is currently hindering their broad use. Nevertheless, low toxicity, a broad spectrum of biological activity, and the ability to bind heavy metals portends with great promise their use in medicine, the food industry, agriculture, and biotechnology, including environmental protection.A comparison of the sorption capabilities of the chitin-melanin glucan complex Mikoton from higher basidiomycetes, chitin-and chitosan-melanin complexes from dead bee bodies, and chitosan isolated from crab shells showed [5, 6] that polymeric sorbents containing melanin were most effective for radionuclides. The distribution coefficients (K d ) obtained for 233 UO 2 2+ by using melanin-containing complexes of various origin ranged from 1.2·10 3 to 8.1·10 3 mL/g whereas K d values for chitosan were less than 5.8·10 2 mL/g. An analogous dependence was observed for 90 Sr 2+ .
