Leaching of Cs and Sr from Sewage Sludge Ash Buried in a Landfill Site

Abstract

Radionuclide contamination from the nuclear accident at the Fukushima Daiichi Nuclear Power Plant has been found in sewage sludge ash produced in eastern Japan. When such contaminated waste contains less than 8,000 Bq/kg radiocesium, it is being disposed in controlled landˆll sites. In order to assess the possible spread of the radionuclides by their leaching from the landˆll sites, it is important to know the leaching behavior of the radionuclides from the sewage sludge ash and factors in‰uencing the leaching behavior. In this study, leaching experiments using stable Cs and Sr were conducted for sewage sludge ash under several conditions to investigate eŠects of chemical composition of leachate, pH, and solid/liquid ratio on Cs and Sr leaching behaviors. In the pH range from 6 to 12, the leaching ratio of Cs or Sr was less than 5.2 or 0.21, respectively. Additionally, the leaching ratio of Sr decreased with increasing pH of the leachate. In contrast, the higher the pH in the leachate was, the higher the leaching ratio of Cs was. Finally, possible radionuclide leaching from contaminated sewage sludge ash and then radionuclide concentrations in an actual landˆll leachate were assessed. It could be suggested that 90 Sr leaching from the landˆll site had the least eŠect on the environment, whereas 134＋137 Cs leaching needed to be taken into account for spreading radioactive materials from the landˆll site to the environment.