Chemical characteristics and leachability of organically contaminated heavy metal sludge solidified by silica fume and cement

This paper discusses the development of mixtures with silica fume as a stab ilization/solidification agent and binder for industrial wastewater residue containing organic and heavy metal contaminants. The UCS (Unconfined Compr essive Strength) gradually increased to 66.7% as the silica fume content in creased to 15%. The leaching of TOC and chromium decreased as more OPC was substituted with silica fume. When the mix had 5% silica fume, it retained about 85% TOC, and chromium leached out 0.76mg-Cr/g-Cr in acidic solution. Also, microstructural studies on the solidified wastes through the scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) and X-ray dif fraction analysis showed that the silica fume caused an inhibition to the e ttringite formation which did not contribute to setting, but coated the cem ent particles and retarded the setting reactions. The results indicated tha t the incorporation of silica fume into the cement matrix minimized the det rimental effects of organic materials on the cement hydration reaction and contaminant leachability.