PHYSICAL, CHEMICAL AND STRUCTURAL EVOLUTIION OF ZEOLITE-CONTAINING WASTE FORMS PRODUCED FROM METAKAOLINITE AND CALCINED SODUIM BEARING WASTE (HLW AND/OR LLW)

Grutzeck, Michael W.

Pittsburgh State University, University Park, PA (United States)

关键词: Building Materials;    Zeolites;    12 Management Of Radioactive Wastes, And Non-Radioactive Wastes From Nuclear Facilities;    Waste Forms;    Bearings;   

DOI  :  10.2172/834996
RP-ID  :  EMSP-81963-2003
RP-ID  :  FG07-98ER45726
RP-ID  :  834996

美国|英语

来源: UNT Digital Library

【 摘 要 】

Zeolites can adsorb liquids and gases, take part in catalytic reactions and serve as cation exchange media. They are commercially available as finely divided powders. Using zeolites to manage radioactive waste is not new, but a process by which zeolites can be made to act both as a host phase and a cementing agent is. It is notable that zeolites occur in nature as well consolidated/cemented deposits. The Romans used blocks of Neapolitan zeolitized tuff as a building material and some of these buildings are still standing. Zeolites are easy to synthesize from a wide range of both natural and man-made precursor materials. The method of making a ''hydroceramic'' is derived from a process in which metakaolinite (thermally dehydroxylated kaolinite) is slurried with a dilute sodium hydroxide (NaOH) solution and then reacted for hours to days at mildly elevated temperatures (60-200 C). The zeolites that form in solution are finely divided powders containing micrometer sized crystals. However, if the process is changed and only enough concentrated sodium hydroxide solution (e.g. 12 M) is added to the metakaolinite to give the mixture a putty-like consistency and the mixture is then cured under similar conditions, the mixture becomes a very hard ceramic-like material containing distinct tectosilicate crystallites (zeolites and feldspathoids) imbedded in an X-ray amorphous sodium aluminosilicate hydrate matrix. Due to the material's vitreous character, the composite has been called a hydroceramic. Similar to zeolite/feldspathoid powders, a hydroceramic is able to sequester cations and a wide range of salt molecules (e.g., nitrate, nitrite and sulfate) in lattice positions and within structural channels and voids thus rendering them ''insoluble'' and making them an ideal contingency waste form for solidifying radioactive waste. The obvious similarities between a hydroceramic waste form and a waste form based on solidified Portland-cement grout are superficial because their chemistries are entirely different. In addition to being vastly superior to conventional Portland cement grouts with respect to salt retention, standard radwaste leach protocols (PCT, TCLP) have shown that hydroceramics also do a better job of immobilizing the RCRA-toxic and radioactive components of liquid sodium bearing waste (SBW) now in storage at DOE's Hanford, Savannah River and Idaho sites.