Geopolymers for the Immobilization of Radioactive Waste
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CC8.35.1
Geopolymers for the Immobilization of Radioactive Waste D S Perera, M G Blackford, E R Vance, J V Hanna, K S Finnie and C L Nicholson* Australian Nuclear Science and Technology Organisation, PMB 1, Menai, NSW 2234, Australia. *Industrial Research Ltd., PO Box 31-310, Lower Hutt, New Zealand. ABSTRACT Geopolymers are made by adding aluminosilicates to concentrated alkali solutions for dissolution and subsequent polymerization to form a solid. They are amorphous to semicrystalline three dimensional aluminosilicate networks. Although they have been used in several applications their widespread use is restricted due to lack of long term durability studies and detailed scientific understanding. Three important tools for the study of geopolymers are transmission electron microscopy (TEM), solid state magic angle spinning nuclear magnetic resonance (MAS NMR) and infra red (IR) spectroscopy. Cs and Sr are two of the most difficult radionuclides to immobilize and are therefore suitable elements to study in assessing geopolymers as matrices for immobilization of radioactive wastes. In this study Cs or Sr was added to geopolymer samples prepared using fly ash precursors. A commercial metakaolinite geopolymer was studied for comparison. The geopolymers were mainly amorphous as shown by TEM, whether they were made from fly ash or metakaolinite. In the fly ash geopolymer, Cs preferentially inhabited the amorphous phase over the minor crystalline phases, whereas Sr was shared in both. The MAS NMR showed that Cs is held mostly in the geopolymer structure for both fly ash and metakaolinite geopolymers. The IR spectra showed a slight shift in antisymmetric Si-O-Al stretch band to a lower wavenumber for the fly ash geopolymer, which implies that more Al is incorporated in this geopolymer structure than in the metakaolinite geopolymer.
INTRODUCTION Geopolymers are made by adding aluminosilicates to concentrated alkali solutions for dissolution and subsequent polymerization to take place. They consist of amorphous to semicrystalline three dimensional aluminosilicate networks [1]. Their physical behaviour is similar to that of Portland cement and they have been considered as a possible improvement on cement in respect of compressive strength, resistance to fire, heat and acidity, and as a medium for the encapsulation of hazardous or low/intermediate level radioactive waste (LLW/ILW) [2, 3]. Although they have been used in several applications their widespread use is restricted due to lack of long term durability studies and detailed scientific understanding. Geopolymers are mostly amorphous, therefore infra red (IR) spectroscopy, solid state magic angle spinning nuclear magnetic resonance (MAS NMR) and transmission electron microscopy (TEM) are important tools to investigate their structure. We applied these techniques to geopolymers containing either Cs or Sr (~ 1wt%), which are significant elements in many LLW/ILW and are difficult to immobilize.
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EXPERIMENTAL The batch compositions of the fly ash geopolymer consi
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