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Continuous-Melter Vitrification of Fernald Mixed Wastes: Distribution of Contaminants Between Glass, Scrubber Solutions and Off-Gases

Published online by Cambridge University Press:  25 February 2011

Keith S. Matlack
Affiliation:
Vitreous State Laboratory, The Catholic University of America, Washington, DC.
Hamid Hojaji
Affiliation:
Vitreous State Laboratory, The Catholic University of America, Washington, DC.
Sabrina S. Fu
Affiliation:
Vitreous State Laboratory, The Catholic University of America, Washington, DC.
Ian L. Pegg
Affiliation:
Vitreous State Laboratory, The Catholic University of America, Washington, DC.
Pedro B. Macedo
Affiliation:
Vitreous State Laboratory, The Catholic University of America, Washington, DC.
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Abstract

Results are presented from treatability studies on the vitrification of hazardous and low-level radioactive soils and sludges from the Fernald site. The majority of the contaminants of concern are contained in large volumes of sludges accumulated from uranium and thorium production operations that are presently stored in pits at Fernald. These sludges present particular challenges to the vitrification process in that they contain significant amounts of fluorides (mostly magnesium and calcium). In this study, glass formulations used sludges, soils and a minimum amount of additives resulting in waste loadings as high as 94%. Several of these formulations were evaluated by continuous feeding of slurries into a joule-heated vitrification system. Melter off-gases were treated in a two-stage NaOH scrubbing system. HF acid fumes were neutralized, resulting in the formation of a NaF solid precipitate which is removed from the scrubber and recycled to subsequent melter feeds. Elemental and isotope compositions of the glasses, scrubber solutions, NaF precipitate and off-gases show that greater than 99.7% of uranium and thorium, 95% of Pb, Cd, Ni, Sb, Cr, and Hg were retained in the glass. Fluoride and other gaseous emissions from the scrubber system were below regulatory limits, even before HEPA filtration.

Type
Research Article
Copyright
Copyright © Materials Research Society 1994

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