Incorporation Behavior of Cesium into Pollucite and the Optimization of Synthesis Method

For removal and long term storage of radioactive cesium ion (Cs) which diffused into the environment by the Fukushima Daiichi Nuclear Power Plant accident, pollucite (POL: Cs16Si32Al16O96·nH2O) which is a cesium containing mineral was synthesized by using a solution containing sodium silicate, sodium aluminate and cesium chloride, and the optimum synthesis condition for Cs removal and insolubilization was determined. POL synthesis was carried out at 200°C for 24 h, in the Si/Al molar ratio range of 0.5 to 7.0 and in the Cs concentration range of 10 to 5000 mg dm. The product was characterized using X-ray diffractometer and scanning electron microscopy. After synthesis of POL, the concentration of Cs remained in the solution which was not incorporated into POL was determined by using atomic adsorption spectrophotometer. The Cs dissolution experiment was carried out with the synthesized product in a 0.6 M NaCl solution for 24 h. It was revealed that excellent Cs removal and insolubilization were confirmed by the formation of POL with Si/Al molar ratio of 2.0 and 2.5 in the mixed solution adjusted to 2500 mg dm Cs concentration. In addition, even in low Cs concentrations (100 mg dm), the excellent Cs removal and insolubilization were achieved with POL having Si/Al molar ratio of 2.0. Moreover, if Si/Al molar ratio was adjusted to be 2.0 to 2.5, Cs (100 mg dm to 2500 mg dm) could remove effectively and store stably long time.