NRC-8, EuCheMS International Conference on Nuclear and Radiochemistry

Coprecipitation of Radionuclide Microquantities on Chitosans of Different Molecular Masses in Solutions

19 Sept 2012, 18:00

1h 50m

Como, Italy

Poster Radioactive elements in the environment, radiation archeometry and Health Physics Poster Session

Speaker

Prof. Sergey Kulyukhin (Frumkin' Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Russia)

Description

The current approaches to spent nuclear fuel treatment lead to the occurrence of radionuclides in repositories and ponds for the storage of fuel elements. In addition, radionuclides, including the above-mentioned ones, are components of low-activity liquid waste. Despite the efforts taken to localize radioactive compounds, they penetrate into the environment, including the World Ocean. The usage of chitosans and their derivatives as flocculants in sewage water purification from heavy metals, dyes, and surfactants is reported in [1, 2]. The advantages of ashless organic coprecipitators over inorganic ones are described in [3]. The authors showed that the degree of Pu extraction from 0.01 M solutions of HNO3 on high-molecular chitosan (HMC) with MM = 15105 g/mol and low-molecular chitosan (LMC) with molecular masses (MM) = 5103 g/mol is 95% to 99%. Simultaneously, it was established that the coprecipitation degree of 60Co и 54Mn radionuclides ranged from 78% to 85%, and that of 90Sr and 137Cs was 25-30%, irrespective of the MM of the chitosans and the solution compositions. The data on the behavior of other radionuclides during flocculation on chitosans is unavailable in the literature. Based on the above considerations, the aim of this study was to study the behavior of radionuclides during coprecipitation on chitosans from solutions of complex chemical compositions. The possibility of 233U, 239Pu, 241Am, 152Eu, 90Sr, 90Y, and 60Co coprecipitation on chitosans of different MM was studied. At first, the solubility of the obtained chitosans in different media was studied. It was shown that HMC and LMC were insoluble in distilled water and dissolved well at рН < 3. The solubility of chitosans in those solutions ranged from 8 g/l to 10 g/l and 10 g/l to 15 g/l for HMC and LMC, respectively. Increasing the solution рН to 6 for LMC and 8 for HMC resulted in the formation of a bulk thick precipitate. In both cases, the residual chitosan concentration was 0.45 g/l. In sea water at рН = 8.5, the solubility of HMC and LMC decreased to 0.045 g/l. It was found that the efficiency of the sorption of the 233U, 241Am, 152Eu, and 60Co radionuclides on crystallized HMC and LMC from salt solutions is low, with the distribution coefficients Kd being not higher than 100 ml/g after the time of contact between the solid and liquid phases of 1 h and at V/m = 100 ml/g. Since the studied chitosans displayed a low sorptive capacity, our further research was focused on the flocculation coprecipitation of radionuclides. As follow from the data on the 233U, 239Pu, 241Am, 152Eu, 90Sr, 90Y, and 60Co coprecipitation on HMC and LMC in solution, in both cases degree of coprecipitation a of all radionuclides studied, except 60Co and 90Sr, reached virtually peak values at a chitosan concentration of 1 g/l. For HMC, a was 80% for 152Eu and 90Y, 99% for 233U and 241Am, and 85% for 239Pu. In contrast to An, 152Eu, and 90Y, the a for 60Co increased monotonically with increasing the HMC concentration in solution and at [HMC] = 5 g/l, reached 40%. For 90Sr, a was not higher than 3% over the entire chitosan concentration range. For LMC a for An, 152Eu, and 90Y varied insignificantly ranging from 92% to 99%. For 60Co and 90Sr, a increased to 40% in the chitosan concentration range 0-1 g/l. Increasing the [LMC] in solution further on had hardly any impact on a for 90Sr, by increased it monotonically for 60Co. The obtained a values were 40% and 60% for 90Sr and 60Co, respectively, at [LMC] = 5 g/l. A comparison of the results showed that the coprecipitation of all the elements studied was more effective on LMC than HMC. To conclude, using chitosans for concentrating radionuclides from salt solutions could find practical use during not only ecological monitoring of natural waters, but also the reprocessing of low-level liquid waste. The research was carried out using financial support by the Russian Fund for Fundamental Research (Grant N 11-03-00106). References 1. Qiang Yu, Shubo Deng, Gang Yu. Water Research. 42(12) 3089-3097 (2008) 2. Li Wang, Aiqin Wang. Bioresource Technology. 99(5) 1403-1408 (2008) 3. Kosyakov V.N., Veleshko I.E., Yakovlev N.G. et al. Radiochemistry (Russia). 45(4) 366-369 (2003)