Radioactive cesium removal from ash-washing solution with high pH and high K+-concentration using potassium zinc hexacyanoferrate

The effectiveness of K2Zn3[Fe(CN)(6)](2) (KZnHCF) for the radioactive cesium (R-Cs) decontamination from wood ash extract is studied. Because the ash-washing solution is of high pH and high K+-concentration, adsorbent with high pH tolerance and selectivity for Cs+ over coexistent K+ is required. For this purpose, we evaluated the effectiveness of KZnHCF, Prussian blue (PB), and zeolite. With 10,000 mg/L of K+-concentration, the distribution coefficient, K-d of KZnHCF, PB, and zeolite were 719, 4400, and 210 mL/g, respectively. Regarding the pH-effect, KZnHCF shows good Cs adsorption even at pH 12, in contrary, PB is effective only at pH < 9. Actually for the decontamination of ash washed solution with 212 Bq/L of total R-Cs activity and 1000 mL/g of solution to adsorbent ratio, only KZnHCF could reduce the radioactivity to less than 60 Bq/L, the standard of Cs-134 for public waters in Japan. In addition, a theory for predicting the R-Cs adsorption ratio based on the initial concentration of K+, by using the equilibrium coefficient K-eq =71.6 for the ion-exchange between K+ and Cs+ in KZnHCF is proposed. (C) 2016 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.