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Synthesis, Crystal Chemistry and Stability of Ettringite, A Material with Potential Applications in Hazardous Waste Immobilization

Published online by Cambridge University Press:  15 February 2011

Gregory J. McCarthy ,
David J. Hassett  and
Jason A. Bender
Gregory J. McCarthy
Affiliation:
Department of Chemistry, North Dakota State University, Fargo, ND 58105 U.S.A.
David J. Hassett
Affiliation:
Energy and Environmental Research Center, University of North Dakota, Grand Forks, North, Dakota 58202 U.S.A.
Jason A. Bender
Affiliation:
Department of Chemistry, North Dakota State University, Fargo, ND 58105 U.S.A.
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Abstract

Recent results on synthesis, crystal chemistry, structure and stability of ettringite*, with specific reference to use of this material in hazardous waste immobilization, are presented. Ettringites with selenate, chromate, borate, sulfite and carbonate replacing sulfate have been synthesized and characterized by XRD for phase purity and structure. In X-ray powder diffractograms, selenate and chromate etringites have the normal trigonal P31cettringite structure, whereas the borate, sulfite and carbonate ettringites can be indexed on a hexagonal unit cell with a halved c parameter. In excess of 95% of the Se and B in solutions spiked with various concentrations of these elements has been removed by precipitation of ettringite. Ettringites appear to be unstable in solutions outside of the approximate pH range 11.0-12.5, and there is a potential for some oxyanion exchange between ettringites and oxyanion-containing solutions. Buffering of pH, and dissolved Ca, Al and sulfate activities by other components of ettringite-based hazardous waste forms, combined with low-reactivity C-S-H matrices, could largely mitigate these concerns.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 245: Symposium K – Advanced Cementitious Systems: Mechanisms and Properties , 1991 , 129
Copyright
Copyright © Materials Research Society 1992

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References

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