Characteristics of radioactive cesium extracted from designated waste. Ultrafiltration and coagulation test

We investigated the characteristics of radioactive cesium (rad-Cs) extracted from the municipal solid waste contaminated with rad-Cs in the aftermath of the 2011 Fukushima Daiichi Nuclear Power Plant accident. The 0.5M oxalic acid extract of a melting furnace fly ash and 5M HCl extract of an incinerator fly ash (both treating a sewage sludge) were filtered by an ultrafilter with molecular weight cut-off of 5,000 Da. The extract of the incinerator ash was also filtered with the molecular weight cut-off 100,000 Da filter. The permeation coefficient of the cutoff 5,000 Da filter was evaluated using distilled water and an acid extract of a sewage sludge ash, spiked with vitamin B12, an organic molecule with known molecular weight. The results indicated that the 5M HCl extract of the incinerator fly ash probably contained some non-ionic (high molecular weight) rad-Cs. However, because of the formation of a gel layer on the ultrafilter during the filtration of the extract, rad-Cs in the higher molecular weight fraction could have been overestimated. Ultrafiltration under more stable conditions will be conducted in our future research to obtain more accurate estimate of the amount of non-ionic rad-Cs in the waste extracts. We also conducted the coprecipitation-coagulation tests using ferrocyanide and a coagulant to remove rad-Cs from the retentate and filtrate obtained after the ultrafiltration. (author)