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Seawater Leachability Of Cement Solidified Heavy Metal Wastes

Published online by Cambridge University Press:  22 February 2011

Tahar Elkorchi ,
Kristine Campbell  and
David Gress
Tahar Elkorchi
Affiliation:
Department of Civil Engineering, Worcester Polytechnic Institute, Worcester MA 01609
Kristine Campbell
Affiliation:
Metcalf, & Eddy Inc., wakefield, MA, 01888
David Gress
Affiliation:
Department of civil Engineering, University of New Hampshire, Durham, N.H. 03824
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Abstract

The seawater leachability of portland cement solidified cadmium and lead wastes is investigated. The synthetic seawater leachates were analyzed for metals content using atomic absorption spectrophotometry. The pH and alkalinity of the leachate was also measured. The cumulative cadmium release after 46 days of leaching was approximately 1.0 percent of the initial total amount added to the portland cement mixture. Lead was not detected in the leachate. The pH was initially higher and the alkalinity lower and subsequently approached the pH and alkalinity values for seawater after 30 days of leaching.

The microstructure of the solidified waste was investigated using the SEM, XRD, MIP and helium pycnometry. Cadmium was detected as cadmium hydroxide while lead was not detected in crystalline form. The total porosity of cadmium and lead wastes were similar however the cadmium waste had a higher volume of pores larger than 0.2 microns.

During the leaching process the surficial microstructure of the solidified waste exhibited a dynamic layer of calcite, aragonite and brucite while the internal structure showed large amounts of ettringite crystals in the cadmium waste only which caused excessive expansion and cracking. A proposed leaching mechanism experienced by the solidified waste is related to the microstructural characteristics of the matrix.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 137: Symposium P – Pore Structure and Permeability of Cementitious Materials , 1988 , 369
Copyright
Copyright © Materials Research Society 1989

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