Radioactive fallout cesium in sewage sludge ash produced after the Fukushima Daiichi nuclear accident. (1st January 2015)

• Record Type: Journal Article
• Authors: Kozai, Naofumi; Suzuki, Shinichi; Aoyagi, Noboru; Sakamoto, Fuminori; Ohnuki, Toshihiko
• Is Part Of: Water research. Volume 68(2015)
• Page Start: 616
• Page End: 626
• Publication Date: 2015-01-01
• Subjects: Sewage sludge ash -- Cesium-137 -- Fukushima -- Dissolution -- Iron -- Silicate; Water -- Pollution -- Research -- Periodicals; 363.7394
• DOI: 10.1016/j.watres.2014.10.038
• Languages: English
• ISSNs: 0043-1354

Abstract

Abstract: The radioactive fallout cesium ( 137 Cs) in the sewage sludge ashes (SSAs) produced in Japan after the Fukushima Daiichi Nuclear Accident was tested. Five samples of SSAs produced in 2011 and 2012 were tested. Two of the samples contained 137 Cs (23 and 9.6 kBq/kg, respectively) above the radioactivity criterion (8 kBq of radioactive Cs/kg of solid) for controlled landfill disposal in Japan. The mineral components of SSA are roughly divided into two groups: an HCl-soluble phase mainly composed of phosphates and oxides; and silicates, including quartz, feldspar, and clay. Both phases contained 137 Cs. The majority (up to 90%) of 137 Cs was contained in the HCl-soluble phase. Among the HCl-soluble subphases, Fe-bearing phases that were probably iron oxides were mainly responsible for 137 Cs retention. No positive evidence was obtained that showed that phosphate-bearing phases, which were included most in SSAs along with the silicate phase, retained 137 Cs. Pre-pulverizing SSAs and heating them at 95 °C in a 6 M or a concentrated aqueous HCl was the most effective method of dissolving the HCl-soluble phase. The radioactivity concentrations of 137 Cs in all the HCl-treatment residues were below the radioactivity criterion. This residue was mostly composed of silicates. After static leaching tests of the residue at 60 °C for 28 days, no 137 Cs was detected in simulated environmental water leachates (pure water and synthetic seawater), demonstrating that 137 Cs in the residue is very stably immobilized in the silicates. Highlights: The Fukushima Nuclear Accident contaminated sewage sludge ash (SSA) with 137 Cs. 137 Cs in SSAs accumulates in iron oxides and silicates. Heating SSA powder in HCl dissolves iron oxides and removes 80–90% of 137 Cs. The remaining Cs is fixed in the HCl-treatment residue (quartz and feldspar). The Cs in the residue is non-leacheable to environmental water.