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Laboratory Modeling and XRD Characterization of the Hydration Reactions of Lignite Gasification and Combustion Ash Codisposal Waste Forms

Published online by Cambridge University Press:  25 February 2011

P. Kumarathasan  and
Gregory J. McCarthy
P. Kumarathasan
Affiliation:
Department of Chemistry, North Dakota State University, Fargo, ND 58105
Gregory J. McCarthy
Affiliation:
Department of Chemistry, North Dakota State University, Fargo, ND 58105
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Abstract

Cementitious reactions in gasification and combustion ash derived from North Dakota lignite permit the fabrication of monolithic wastes forms from nonhazardous ash by-products and hazardous liquid wastes from a coal gasification plant. To better understand such cementitious reactions, x-ray diffraction has been used to characterize the hydration reaction products of crystalline phases in the gasification and combustion ashes from the Beulah, ND, complex and the crystalline reaction products formed. A cementitious lignite fly ash was also studied. pH of solutions at a liquid to solid ratio of 2.4 and times up to 14 days was measured, and compared to pH calculated from leachate chemical analyses. Reactions were monitored for up to one year. Among the principal crystalline phases in gasification ash, carnegieite (Na1.5Al1.5Si0.5O4) was the most reactive. Solution pH's for two samples of gasification ash were in excess of 13; carnegieite reaction may be responsible in part for these very high pH's. Hydration products included gaylussite, (Na2 Ca(CO3)2·5H20), a carbonate-sulfate ettringite structure phase, calcite and three or more zeolites (NaA, laumontite, faujasite and/or NaX). Ettringite and calcite were the principal hydration reaction products of scrubber ash, fly ash and the composite codisposal waste form. The formation of ettringite may be one of the principal reactions responsible for consolidation of the waste forms (along with noncrystalline calcium silicate hydrate formation which could not be observed by XRD). Ettringite was observed to decrease in abundance at long reaction times. Calcium aluminate monosulfate hydrate formed in the later stages of the fly ash reaction.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 86: Symposium N – Fly Ash and Coal Conversion By-Products III , 1986 , 159
Copyright
Copyright © Materials Research Society 1987

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References

REFERENCES

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