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.