No abstract
The results of research on the most effective conditions for removing cesium from soil are presented. The effect of the type and concentration of reagent as well as the duration of treatment (leaching) and temperature on the degree of decontamination is studied. It is shown that autoclave leaching with temperature raised to 160°C to decontaminate 137 Cs contaminated soil is effective. The process conditions for 99% decontamination are determined. Combining reagent treatment under the conditions chosen and hydro-separation removal of the sludge fraction makes it possible to reach a decontamination coefficient of 230 with 10-fold smaller radwaste volume.Methods of soil decontamination based on different principles and mechanisms are being developed and tested in order to rehabilitate territories contaminated with radionuclides and to reduce radwaste storage volumes. One promising method is reagent treatment of the contaminated soil followed by concentration of the extracted radionuclides from the liquid phase by a sorption or precipitation method [1,2]. The effectiveness of reagent decontamination depends on the composition of the soil and ground, the type of contaminating radionuclide and the strength of its bond with the soil components. It is especially difficult to extract 137 Cs, because it is strongly fixed by the clayey component of the soil. Washing the contaminated soil with a solution of different salts does not decrease the specific activity to the required level [3]. Higher decontamination can be attained by treating the soil with a water solution of an acid, for example, nitric acid, in the presence of ammonium or sodium fluoride on account of the destruction of the soil matrix [4]. But this method is not cost-effective because the volatile fluorine compounds are highly aggressive. It is difficult to organize a closed cycle with respect to the leaching solution and the reagent consumption is high. A reagent based on sulfuric acid with no fluorine compounds is free of these drawbacks and makes it possible to attain high cesium extraction with significantly lower specific consumption of the reagent and safe conditions for implementing the method [2,5]. Soil treatment with sulfuric-acid solution at elevated (to 90°C) temperature makes it possible to remove 75-99% of the 137 Cs.The present work is devoted to studying the possibility of further increasing the effectiveness of cesium decontamination of soil at higher temperature (to 160°C) using autoclave leaching. Experimental Part. The experimental studies were performed on samples obtained from a contaminated section of the territory of the National Research Center Kurchatov Institute. The soil consisted of a dark-brown suspension with mass 1.24 kg/dm 3 for a volume which was dried in air under normal conditions in an exhaust cabinet. After drying, the soil was comminuted and passed through a sieve with 0.63 mm cells. The fine soil obtained (72%) was blended by careful mixing and used in subsequent experiments. The specific activity of 137 Cs was 69 kBq/k...
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