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There is a large quantity of contaminated soil with radionuclides due to the accident of Fukushima Daiichi Nuclear Power Plant in Japan. Some previous studies reported that Cs + could be desorbed from soil with high efficiency, however, these methods required huge input energy for operating. Therefore, we focused on oxalic acid, which has shown relatively high desorption efficiency in previous thermal treatment, and evaluated the potential of oxalic acid as a leaching reagent to reduce the volume of contaminated soil without heating. MethodsStable isotope Cs + contaminated biotite was retained in plastic bag for 3 months for aging. Oxalic acid was added to the contaminated biotite and the mixture was maintained around 20 °C. After each leaching time, the mixture was separated using filter paper and the concentration of Cs + in filtrate was measured. Structural changes in biotite before and after leaching were also analyzed. LiNO3 was also used for comparison studies. ResultsThe desorption efficiency of Cs + from biotite by leaching with oxalic acid was 94.9% after 2 weeks and the intensity of the specific reflection for biotite in the X-ray diffractograms decreased with leaching time.These results indicate that oxalic acid can remove Cs + from biotite through the decomposition of the biotite structure. Since LiNO3 desorbed only 32.2% of Cs + as ion-exchangeable form after 2 weeks, oxalic acid can desorb Cs + , which has a strong interaction with biotite such as the inner-sphere complex, without heating. ConclusionAlthough the desorption of Cs + from biotite by leaching with oxalic acid leaching takes a long time, it is a great advantage that this leaching method does not require external energy such as heating. Therefore, oxalic acid leaching has high potential to reduce the volume of contaminated soil with radionuclides.