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Room-temperature adsorption behavior of cesium onto calcium silicate insulation Abstract A calcium silicate insulator material was investigated for its interaction with non-radioactive cesium at room temperature by batch-type adsorption experiments. An industrial-grade calcium silicate was weighted and ground into powder with an average size of 15.4 ± 0.1 µm, which was then placed into polypropylene (PP) tube containing cesium chloride aqueous solution. Cesium concentrations were range between 1.3×10 -6 -3.5×10 -3 M. Adsorption kinetics of cesium was evaluated based on pseudo-first order and pseudo-second order models, while the adsorption isotherm was modeled using the Langmuir model and modified BET model. Physicochemical properties of calcium silicate before and after the adsorption was investigated using XRD, SEM/EDS and FT-IR. Chemisorption was found as the underlying sorption process between calcium silicate insulator material and cesium.

Here, we report an investigation of the gas–solid reaction between cesium hydroxide (CsOH) and siliceous (calcium silicate) thermal insulation at high temperature, which is postulated as the origin for the formation mechanism of cesium-bearing material emitted from the Fukushima Daiichi nuclear power plant. A developed reaction furnace consisting of two heating compartments was used to study the reaction at temperatures of 873, 973, and 1073 K. Under the influence of hydrogen-steam atmospheric conditions (H 2 /H 2 O = 0.2), the reaction between cesium hydroxide vapor and solid thermal insulation was confirmed to occur at temperatures of 973 and 1073 K with the formation of dicalcium silicate (Ca 2 SiO 4 ) and cesium aluminum silicate (CsAlSiO 4 ). Water-dissolution analyses of the reaction products have demonstrated their stability, in particular, CsAlSiO 4 . Constituent similarity of the field-observed cesium-bearing materials near the Fukushima Daiichi nuclear power plants with CsAlSiO 4 suggests for the first time that gaseous reaction between CsOH with calcium silicate thermal insulation could be one of the original formation mechanisms of the cesium-bearing materials.

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