Development of on-site heavy metal analysis method and technology for selective removal of radioactive cesium from the extracts of designated waste
Proceedings of the 15th Workshop on Environmental Radioactivity
High Energy Accelerator Research Organization
School of Science
As a result of the Great East Japan Earthquake and the ensuing Fukushima Daiichi Nuclear Power Plant accident, 31 million t of disaster wastes and municipal solid wastes (MSW) with elevated concentrations of radioactive cesium (rad-Cs) have been generated. The disposal of disaster wastes, except for those in the area near Fukushima Daiichi Nuclear Power Plant, was completed before March of 2014. On the other hand, MSW with rad-Cs concentration higher than 8,000 Bq/kg (designated waste according to Act on Special Measures concerning the Handling of Pollution by Radioactive Materials), total 146,009 t as of June 30, 2014, are piling up in the treatment plant where they were generated. The current report is the summary of our study on the volume reduction technology of the designated waste. Our approach consists of the two step processes, namely, extraction of rad-Cs from the wastes with water or oxalic acid, followed by the selective removal of the extracted rad-Cs using insoluble metal- ferrocyanide (Fer hereafter) co-recipitation technique. Actual MSW extracts often contain high concentrations of multiple transition metals (Fe, Mn, Cu, Zn and Ni). In Fer coprecipitation method, the Cs removal efficiency varies widely depending on the type of metal -Fer precipitate. In other words, the type and concentration of metal contained in the waste extracts should be determined to optimize the Cs removal efficiency of Fer precipitation technique. Anodic stripping voltammetry was successfully applied for on-site determination of heavy metals in the extracts of designated waste. More than 95% rad-Cs removals were achieved for an optimized combination of pH, Fer concentration and type of added metal salts.