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Treatment of Organic-Contaminated Industrial Wastes Using Cement-Based Stabilization/Solidification— Ii. Microstructural Analysis of the Organophilic Clay as a Pre-Solidification Adsorbent

Imperial College Centre for Toxic Waste Management, Imperial College of Science, Technology & Medicine, London, U.K.

C.J. Sollars

Imperial College Centre for Toxic Waste Management, Imperial College of Science, Technology & Medicine, London, U.K.

R. Perry

Imperial College Centre for Toxic Waste Management, Imperial College of Science, Technology & Medicine, London, U.K.

S.E. Tarling

Industrial Materials Group, Crystallography Department, Birkbeck College, London, U.K.

P. Barnes

Industrial Materials Group, Crystallography Department, Birkbeck College, London, U.K.

E. Henderson

Industrial Materials Group, Crystallography Department, Birkbeck College, London, U.K.

In the preceding paper detailed microstructural studies were presented of some fundamental aspects of the interactions of two organic compounds on a cement matrix. Organophilic clays are now attracting increasing attention as potential pre-solidification adsorbents to reduce adverse organic-cement interactions in solidification/stabilization (S/S) systems. This paper presents extensive microstructural studies of interactions between an organophilic clay, containing adsorbed organic wastes, and a cement matrix. Such interactions must be as fully understood as possible if the long-term integrity of the organophilic clay/cement mixes, in whatever formulation, is to be assured in S/S applications.

A range of mixes was made up with the objective of characterizing the interaction of the organophilic clay with phenolic compounds and cement using microstructural methods. This approach was adopted in order to enable essential comparisons to be made between clay-containing and clay-free S/S mixes, using the same organics in both cases. Microstructural studies of organic-free cement/clay mixes showed that the presence of the clay caused an inhibition of the initial ettringite formation, up to seven days, but once ettringite had begun to form it increased to 140% of that in OPC paste at 28 days. Scanning electron microscopy (SEM) micrographs showed that the whole fracture surface was covered with a mat of needle shaped crystals approximately 1 µm in length. These results indicated that the incorporation of clay into the cement matrix may cause the strength reduction observed in macrostructural studies by altering the cement hydration reaction. Microstructural analysis of the solidified (post-adsorption) 3-chlorophenol showed that its detrimental effects on the cement hydration reaction were minimized, provided that the maximum adsorption capacity of the clay was not exceeded.

Key Words: Cement-based solidification • organophilic clay • phenols • microstructural analysis

Waste Management & Research, Vol. 9, No. 1, 113-125 (1991)
DOI: 10.1177/0734242X9100900116


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