Selective Uptake of Sr and Stable Solidification Using Potassium Titanates

The development of selective adsorbents for radioactive Sr ions is one of the most important subjects for the safety decontamination in Fukushima NPP-1[1]. In this study, the selective adsorption properties of Sr, characterization and stable solidification were clarified by using the novel adsorbent of potassium titanates (KT-1). The adsorption properties of Sr2+ ions for original and calcined specimens were examined by batch method under the following conditions; V/m = 100 cm3/g, Mixed solution: 10,000 ppm Na+, 10 ppm Cs+, 10 ppm Ca2+, 1 ppm Mg2+ and 1 ppm Sr2+, 85Sr tracer: 5,000 cpm/cm3, centrifugation: 2,500 rpm, 25°C, shaking time: 1∼24 h, calcination temp.: 300∼900°C. Relatively large uptake percentage above 90% was obtained for the original and calcined specimens below 800°C, while the Sr uptake for calcined specimens above 900°C was lowered due to the thermal decomposition of K2Ti2O5·xH2O. The Sr distribution in the column was examined by flowing the mixed solution through the columns packed with KT-1. The Sr distribution profiles were obtained by the measurement of γ-activity in the column at 5 mm intervals. In either case, no breakthrough of Sr was observed. The distribution profile tended to smooth with increasing flow rate; Sr adsorption band and flow rate have a linear relationship. The leachability of Sr for the solid forms was further examined under the following leaching conditions; leachant: pure water and 1 M HCl; leachant temp.: 25°C and 90°C, leaching period: 4 weeks; calcining temp.: 500∼1,100°C. The leached percentage of Sr in pure water was less than the detection limit of ICP-AES, and that in 0.1 M HCl tended to markedly decrease with calcining temperature; the formation of SrTiO3 phase above 800°C was effective for the lowering of leachability. The novel adsorbent of KT-1 is thus effective for the selective decontamination and stable solidification of Sr in Fukushima NPP-1.

Crystallization and Properties of Glass-Ceramics of the K2O-BaO-B2O3-Al2O3-TiO2 System

Crystallization behavior and properties of glass-ceramics with content (mol%) of: K2O = 3-25, BaO = 3-27, B2O3= 8-26, Al2O3= 13-18, and TiO2= 31-47 were studied. The relation between the initial composition and the formation of the crystalline phases was analyzed. When increasing [Al2O3] and [BaO], was increased the temperature of crystallization; likewise, different barium potassium titanates appeared with [BaO] = 3-13 (Group 1), whereas, different barium titanates were obtained with [BaO] =13-30 (Group 2). The influence of chemical composition on the properties of density, mechanical strength, chemical durability and dielectric properties (dielectric constant and dielectric losses), was discussed. Glass-ceramics with high mechanical resistance in the range of 189-480 MPa and permittivity values between 4.03 and 25.31, and dielectric losses < 2 x 10-4at 1MHz were produced.