The Fukushima Daiichi Nuclear Power Plant accident caused severe soil contamination by radioactive cesium (Cs). The large volume of removed soil from decontamination must be disposed of by 2045, requiring volume reduction. However, Cs is strongly adsorbed onto clay minerals in the soil, making removal difficult. Thus, the desorption behavior of stable Cs adsorbed onto weathered biotite (WB), a clay mineral abundant in Fukushima soils, was investigated using a mechanochemical (MC) method that combines physical grinding by ball impact and friction with a wet process promoting chemical reactions. The effectiveness of this method for desorbing radioactive Cs from Fukushima soil was also evaluated. The results are based on the scanning electron microscopy analysis and the results of the desorption experiment; oxalic acid desorbed Cs to some extent without affecting the layered structure of the clay minerals significantly, and ammonium chloride showed an exfoliation of the layer structure, resulting in a stable desorption of Cs independent of samples. Regarding the real soil samples collected in Fukushima, the MC method using ammonium chloride solution desorbed 80% of 137Cs, and the desorption behavior was reproduced reliably in actual soil samples. In contrast, oxalic acid did not always result in radioactive Cs made sufficiently desorbed for all the samples. Based on these findings, the MC method with ammonium chloride promotes radioactive Cs desorption effectively from interlayers due to synergistic effects from the layered structure’s exfoliation and chemical interaction. The MC method with ammonium chloride should reduce the volume of removed soil requiring final disposal, thereby reducing associated management costs.

Kaolinite- and halloysite-potassium acetate complexes were synthesized by cogrinding with solid potassium acetate (mechanochemical intercalation). The efficiency of mechanochemical intercalation was compared to the intercalation in solution and by homogenization. The effects of ageing and grinding parameters (grinding time, sample:grinding body mass ratio (SGMR), rotational speed) and the humidity on the intercalation were studied. The degree of intercalation increased exponentially with ageing of the samples prepared by mechanochemical and homogenization techniques. For the mechanochemical and homogenization techniques the required amount of potassium acetate per gram of kaolin (∼0.4 g/g) was two orders of magnitude lower than that for the solution intercalation (78.6 g/g). The highest degree of intercalation (86%) and the lowest structural deformation were achieved by the mechanochemical method (¼ h of co-grinding with 1:2 SGMR at 300 rpm), followed by 16 h ageing at 57% relative humidity.