PHYSICAL, CHEMICAL AND STRUCTURAL EVOLUTION OF ZEOLITE-CONTAINING WASTE FORMS PRODUCED FROM METAKAOLINITE AND CALCINED HLW

Grutzeck, Michael W. ; Kwan, Stephen

The Pennsylvania State University, University Park, PA (United States)

关键词: Zeolites;    12 Management Of Radioactive Wastes, And Non-Radioactive Wastes From Nuclear Facilities;    Hydroxides;    Liquid Wastes;    Sodium Hydroxides;   

DOI  :  10.2172/833240
RP-ID  :  EMSP-65366--2001
RP-ID  :  FG07-98ER45726
RP-ID  :  833240

美国|英语

来源: UNT Digital Library

【 摘 要 】

Natural and synthetic zeolites are extremely versatile materials. They can adsorb a variety of liquids and gases, and take part in cation exchange reactions. Zeolites are relatively easy to synthesize from a wide range of natural and man-made materials. One such combination is a mixture of metakaolinite and concentrated sodium hydroxide solution. Once mixed and cured at elevated temperatures, these ingredients react to form a hard, dense, ceramic-like material that contains significant amounts of crystalline tectosilicates (zeolites and feldspathoids) imbedded in an X-ray amorphous sodium aluminosilicate hydrate matrix. This rather unique composite material has been termed a ''hydroceramic.'' The crystalline phases in the hydroceramic have the ability to sequester alkali, alkaline earth and a variety of higher valance cations in lattice positions or within networks of channels and voids. The matrix plays host to the crystallites and to residual amounts of insoluble hydroxide phases. Due to its gel-like character, the matrix also provides considerable strength. A previous publication has established the fact that a mixture of a calcined equivalent ICPP waste (sodium aluminate/hydroxide solution containing {approx}3:1 Na:Al) and fly ash and/or metakaolinite could be cured at various temperatures to produce a monolith containing Zeolite A (80 C) or Na-P1 plus hydroxy sodalite (130 C) dispersed in the alkali aluminosilicate hydrate matrix. Dissolution tests (PCT type) have shown these materials have superior retention of alkali, alkaline earth and heavy metal ions. The zeolitization process is a simple one. Metakaolinite is mixed with a calcined sodium-bearing waste and enough water to make a thick paste. The paste is transferred to a metal canister and ''soaked'' for a few hours at 90 C prior to conventional oven heating or steam autoclaving at -200 C for varying periods of time. Hydroceramics could well be a viable alternative for fixation of low activity sodium-bearing waste (SBW) calcines. The objective of the current study is to adapt this technology for use on site remediation and clean up of caustic waste solutions now in storage in tanks at Hanford and Savannah River. The proposed work is meant to develop a clearer understanding of the advantages and limitations of producing a zeolite-containing hydroceramic from treated low activity SBW, i.e. the effect of processing variables, reaction kinetics, crystal and phase chemistry, and microstructure on the performance of the waste form.