As one of major deficiencies in cement-based waste stabilization/solidification (S/S) processes is their difficulty in treating inorganic wastes containing organic material, reactive mineral admixtures and organophilic clays are studied as potential pozzolanic reagents and pre-solidification adsorbents of organic components.
Cement-based stabilization/solidification of hazardous wastes containing heavy metal and organic has been investigated using chrome tannery waste. This work investigated the use of Na-bentonite and briquette ash as adsorbents for the organic components and heavy metals of industrial wastes, and silica-fume as an pozzolanic reagent to improve the solidified wastes with cement. Chrome tannery wastes containing up to 1.5% organic carbon and 1.2% chromium were treated with sodium bentonite and briquette ash. Organic components and heavy metal of wastes were well adsorbed by the adsorbents. Solidification of the waste/clay/silica-fume mixes produced a monolithic mass with high strength and very low leaching of the organic compounds and the metals. This study has shown that Na-bentonite and briquette ash could be successful adsorbents for the organic contaminant and heavy metals in industrial wastes and enabled them to be treated by cement-based solidification. Also the use of silica-fume to get high compressive strength and low penetration was highly effective. Cement-based solidification with the Na-bentonite, briquette ash, and silica-fume gave solid products which set rapidly and were far stronger and more homogeneous than the sole cement-based solidification. Leaching organic compounds and heavy metal from the stabilized products were very low. The TOC was reduced by 60% to 78% for the wastes tested compared with the conventional cement-based solidified waste, and the release of heavy metal was reduced by 52% to 70%.
This paper presents microstructural studies of interactions between silica fume, Na-bentonite, containing adsorbed organically contaminated harzardous wastes, and a cement matrix. Such interactions must be as fully understood as possible if the long-term integrity of the silica fume/organophilic clay/cement mixes, in whatever formulation, is to be assured in S/S applications.
The scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) analysis of the wastes/OPC mix showed that the ettringite crystals were in needle shape deposited in the voids or on the surface of hydration material. Microstructural studies of solidified wastes with silica fume and/or Na-bentonite showed that their presence caused an inhibition to the ettringite formation. The results indicated that the incorporation of silica fume and/or Na-bentonite into the cement matrix minimized the detrimental effects of organic materials on the cement hydration reaction.