Reagent-based remediation of soil contaminated with transuranium elements

Abstract

The results of studies on selecting remediation solutions for removing plutonium and americium from soil are presented. The effect of the type and concentration of different reagents on the degree of leaching of radionuclides is studied. It is shown that acid solutions extract americium from soils. Reducing media must be used to extract plutonium from soils efficiently. The conditions for obtaining 90% reagent-based remediation of soils are determined.To remediate grounds contaminated with radionuclides, special technologies for decontaminating soils and subsoils must be developed. The removal and direct disposal of the surface soil layer in a repository are not cost-effective, since the contaminated soil is low-level radwaste in most cases. Technologies for remediating soils based on physical and chemical methods of removing radioactive contamination are being developed and tested, since there is need for soil remediation and the volume of radwastes which are to be placed in long-term storage repository must be reduced. The physical method based on removing soil by separating the fine fraction, which contains most of the radionuclide mass, has been implemented at the National Research Center Kurchatov Institute.The chemical method consists in desorbing the radionuclides during treatment of the contaminated soil by a solution of a special reagent. The reagent method, characterized by a high decontamination factor (~20) as compared with the separation method (~5), can be used alone as well as for additional, deeper, cleaning of soil after the fine fraction has been separated.The main problems in developing the reagent technology are finding an effective composition for the extracting agent and determining the conditions for transferring the radionuclides into solution. The reagents and conditions for effective decontamination of soil contaminated with 137 Cs and 226 Ra with better than 90% removal have been determined in previous work [1,2]. In the present article, we present the results of studies of the reagent-based remediation of soils contaminated with plutonium and americium.Experimental Part. The investigations were performed on samples of real soil which were obtained from the surface of a contaminated section on the grounds of an atomic energy enterprise from depths to 30 cm. Average samples of airdried soil were used for the experiments. The particle-size composition was determined by the pipette method. The form in which the plutonium and americium were present in the soil was determined by methods based on successive treatment of the samples by reagent solutions with different composition in order of increasing chemical activity [3].Laboratory experiments for choosing desorbing reagents were performed under static conditions by allowing a weighed portion of the air-dried soil to come into 24-h contact with a water solution of salts and mineral acids at 20°C and S:L = 1:5 for the contact phases. Next, the liquid and solid phases were divided by filtering and analyzing the plutonium and