SPECIATION OF CADMIUM IN CEMENT. PT.1. Cd2+ UPTAKE BY C-S-H

Hazardous cadmium can be trapped in C-S-H, the main "phase" in Portland cement. Two kinds of Cd-containing calcium silicates were synthesised: Cd/Ca silicate hydrates prepared by coprecipitation and Cd-exchanged C-S-H. In Cd-exchanged C-S-H, chemical and structural studies (ICP-AES, XRD, E...

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Bibliographic Details
Published in:Cement and concrete research 2001-01, Vol.31 (4), p.563-569
Main Authors: Pomies, M-P, Lequeux, N, Boch, P
Format: Article
Language:English
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Summary:Hazardous cadmium can be trapped in C-S-H, the main "phase" in Portland cement. Two kinds of Cd-containing calcium silicates were synthesised: Cd/Ca silicate hydrates prepared by coprecipitation and Cd-exchanged C-S-H. In Cd-exchanged C-S-H, chemical and structural studies (ICP-AES, XRD, EXAFS, and NMR) show that up to 30 wt% Cd uptake is possible, with little structural change. XRD patterns and 29Si MAS NMR spectra are similar in Cd-free and Cd-containing C-S-H. Cd-EXAFS shows that the majority of Cd2+ atoms are homogeneously distributed within the C-S-H structure, although 113Cd cross-polarisation (CP) MAS NMR cannot discriminate between Cd atoms in the main layer and Cd atoms in the interlayer. In Cd/Ca silicate coprecipitates, the structure is nearly amorphous and the silicate species do not polymerise to a C-S-H-like structure. 28 refs.
ISSN:0008-8846