Sorption and desorption studies of Cs and Sr in contaminated soil samples around Fukushima Daiichi Nuclear Power Plant

Purpose Huge amounts of radiocesium, radiostrontium, and fission products were released into the atmosphere during the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident. Therefore, it is necessary to determine the distribution coefficient of Cs and Sr in the soil-water system around FDNPP from the viewpoint of their migration. Materials and methods The determination of sorption coefficient K-d(S) as well as desorption coefficient K-d(D) for Cs and Sr has been carried out in the present study using the laboratory batch method. In this experiment, stable Cs and Sr were used for sorption on contaminated Fukushima soil samples and groundwater collected in proximity to the soil sample sites. Different soil parameters were measured to understand their effect on the sorption and desorption processes. Desorption experiments were carried out on some selected contaminated soil samples. Results and discussion K-d(S)-Cs and K-d(S)-Sr varied from 65 to 2100 L/kg and 15 to 130 L/kg, respectively. K-d(D)-Cs and K-d(D)-Sr varied between 75-2500 and 10-120 L/kg, respectively. High values of sorption coefficients for Cs indicate sorption capacity of soils for Cs is more than Sr. For Cs, K-d(D) was higher than K-d(S) whereas for Sr, K-d(S) was either equal to or higher than K-d(D). A moderate Pearson's correlation of (K-d) Cs and Sr with exchangeable cations (Al, K, Mg, and Na) supported that ion exchange sorption mechanism is significant. There is enhanced Cs sorption compared to Sr due to the presence of biotite, kaolinite and smectite minerals resulting in high mobility of Sr in the Fukushima environment. Conclusions We concluded retention capacity of Fukushima soils for Cs is moderately stronger than Sr, which supports Sr is more mobile in the environment.