SORPTION OF 90Sr AND 137Cs FROM THE MODEL SOLUTIONS OF LIQUID RADIOACTIVE WASTES ON NATURE AND MODIFIED ZEOLITES OF SOKIRNITSKE DEPOSIT

Abstract

The liquid radioactive waste (LRW) management at the Ukrainian nuclear power plants is an urgent problem since the scheme of treatment of radionuclide-bearing solutions by deep evaporation with subsequent crystallization of radionuclides in the form of soluble salts has a number of serious drawbacks and the final products of the treatment (vat residue, spent sorbents and sludges, salts) do not meet the ac-ceptance criteria for long-term storage and disposal. One of the promising LRW treatment schemes is the one using methods of selective sorption by natural and modified sorbents. The article presents the results of the study of the kinetics of 90Sr and 137Cs sorption by natural, acid- and alkaline-modified zeolites from Sokirnyt’ske deposit. The maximum degree of sorption on natural zeolite during the experiment (14 days) was 55% for 90Sr and 90% for 137Cs. The maximum degree of 90Sr and 137Cs sorption on alkaline-modified zeolite was 62.2% and 98.78%, respectively. For acid-modified zeolite, the maximum sorption degree of 90Sr was 18% and of 137Cs – 85%. Thus, it can be infered that among the studied zeolites, the most effective sorbent of 90Sr and 137Cs is alkaline-modified zeolite (Na-form). Sodium hydrox-ide modification of the natural zeolite increases the sorption degree of both 90Sr and 137Cs by 10 15%. The results of determining the forms of being of the adsorbed radionuclides indicated that the sorption of 90Sr on natural and alkaline-modified zeolites is characterized by up to 20% predominance of ion-exchangeable forms, and sorption on acid-modified zeolite – by the equality of exchangeable and non-exchangeable forms. The sorption of 137Cs on natural and alkaline-modified zeolites is characterized by up to 10% predominance of ion-exchangeable form. In the case of the alkaline-modified zeolite, 10% predominance of non-exchangeable adsorbed cesium form was observed during the first 2 days of the experiment. During the sorption of 137Cs on alkaline-modified zeolite, double predominance of the exchangable form over the non-exchangeable was observed during the whole experiment (14 days).

Keywords

• liquid radioactive wastes
• sorption
• zeolite
• strontium-90