Effect of Oxygen on Radiolytic Hydrogen Production from X-type Zeolite-Water Mixtures

摘要

Effect of oxygen on radiation-induced reactions in zeolite-water mixture was studied, in order to obtain a fundamental understanding on radiolytic hydrogen production from the mixture. Understanding of the radiation effect will provide a basis for safe operations of water treatments using zeolites in nuclear accidents. In this study, the effect of oxygen was investigated because oxygen is an abundant molecule that potentially affects the radiation-induced reactions. The hydrogen production from the mixture of an X-type zeolite with aqueous solution was examined under argon-saturated, aerated, and oxygen-saturated conditions. The hydrogen production from the mixture was decreased by the presence of oxygen, although a considerable production of hydrogen from the zeolite was still observed under oxygen-saturated condition. Three effects of oxygen were proposed based on the observed dependence of hydrogen production on the solid-liquid ratio of the mixture under the different gas conditions. One effect is preventing dissolved aluminum from producing hydrogen. The presence of oxygen decreased the hydrogen production from aqueous solution containing small amounts of the zeolite. The solution contained dissolved aluminum, which produces hydrogen through a reaction with hydrated electron. The decrease in hydrogen production and the observation of aluminum elution indicate that oxygen reacts with hydrated electron in competition with dissolved aluminum. Another effect is inhibition of hydrogen produced from the irradiated zeolite. The inhibiting effect was observed in the irradiation of the zeolite with adsorbed water. Oxygen inhibited the hydrogen production from the hydrated zeolite. The other effect is indirect inhibition of hydrogen by promoting hydrogen peroxide generation. The hydrogen production under oxygen-saturated condition was further inhibited when the zeolite was submerged in water. The further inhibition was interpreted as showing that hydrogen peroxide from the interstitial water inhibited the hydrogen production. The radiolysis of water generates hydrogen peroxide. Oxygen promotes the hydrogen peroxide generation. This interpretation is supported by the observation that the concentration of hydrogen peroxide in the irradiated mixture decreased with increasing solid-liquid ratio. The decrease in the hydrogen peroxide concentration indicates that hydrogen peroxide was involved in the reactions induced by irradiation of the zeolite.