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Open AccessArticle

Treatment Technology of Hazardous Water Contaminated with Radioisotopes with Paper Sludge Ash-Based Geopolymer—Stabilization of Immobilization of Strontium and Cesium by Mixing Seawater

1
Department of Architectural Design and Engineering, Graduate School of Science and Technology for Innovation, Yamaguchi University, Ube 755-8611, Japan
2
Department of Earth Sciences, Graduate School of Science and Technology for Innovation, Yamaguchi University, Yamaguchi 753-8512, Japan
*
Author to whom correspondence should be addressed.
Materials 2018, 11(9), 1521; https://doi.org/10.3390/ma11091521
Received: 28 July 2018 / Revised: 17 August 2018 / Accepted: 19 August 2018 / Published: 24 August 2018
(This article belongs to the Special Issue Materials for Nuclear Waste Immobilization)
Long-term immobilization ratios of strontium (Sr2+) and cesium (Cs+) in paper sludge ash-based geopolymer (PS-GP) were investigated in one year. PS-GP paste specimens were prepared in the conditions of 20 °C and 100% R.H., using two kinds of paper sludge ash (PS-ash). Two kinds of alkaline solution were used in the PS-GP as activator. One was prepared by diluting aqueous Na-disilicate (water glass) with seawater. Another was a mixture of this solution and caustic soda of 10 M concentration. When seawater was mixed into the alkaline solution, unstable fixations of Sr2+ and Cs+ were greatly improved, resulting stable and high immobilization ratios at any age up to one year, no matter what kind of PS-ash and alkaline solution were used. Element maps obtained by EPMA exhibited nearly even distribution of Cs+. However Sr2+ was biased, making domains so firmly related to Ca2+ presence. The mechanism that seawater stabilizes immobilization of Sr2+ and Cs+ was discussed in this study, but still needs to further investigation. Chemical composition analyses of PS-GP were also conducted by SEM-EDS. Two categories of GP matrix were clearly observed, so called N-A-S-H and C-A-S-H gels, respectively. By plotting in ternary diagrams of SiO2-(CaO + Na2O)-Al2O3 and Al2O3-CaO-Na2O, compositional trends were discussed in view of ‘plagioclase gels’ newly found in this study. As a result, it is suggested that the N-A-S-H and C-A-S-H gels should be strictly called Na-rich N-C-A-S-H and Ca-rich N-C-A-S-H gels, respectively. View Full-Text
Keywords: geopolymer; paper sludge ash; radionuclide; hazardous water; immobilization; seawater; strontium; cesium; chlorine geopolymer; paper sludge ash; radionuclide; hazardous water; immobilization; seawater; strontium; cesium; chlorine
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Li, Z.; Nagashima, M.; Ikeda, K. Treatment Technology of Hazardous Water Contaminated with Radioisotopes with Paper Sludge Ash-Based Geopolymer—Stabilization of Immobilization of Strontium and Cesium by Mixing Seawater. Materials 2018, 11, 1521.

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