Utilization of fly ash for stabilization/solidification of heavy metal contaminated soils
- Stevens Inst. of Technology, Hoboken, NJ (United States)
Pozzolanic-based stabilization/solidification (S/S) is an effective, yet economic technological alternative to immobilize heavy metals in contaminated soils and sludges. Fly ash waste materials were used along with quicklime (CaO) to immobilize lead, trivalent and hexavalent chromium present in contaminated clayey sand soils. The degree of heavy metal immobilization was evaluated using the Toxicity Characteristic Leaching Procedure (TCLP) as well as controlled extraction experiments. These leaching test results along with X-ray diffraction (XRD), scanning electron microscope and energy dispersive x-ray (SEM-EDX) analyses were also implemented to elucidate the mechanisms responsible for immobilization of the heavy metals under study. Finally, the reusability of the stabilized waste forms in construction applications was also investigated by performing unconfined compressive strength and swell tests. Results suggest that the controlling mechanism for both lead and hexavalent chromium immobilization is surface adsorption, whereas for trivalent chromium it is hydroxide precipitation. Addition of fly ash to the contaminated soils effectively reduced heavy metal leachability well below the non-hazardous regulatory limits. However, quicklime addition was necessary in order to attain satisfactory immobilization levels. Overall, fly ash addition increases the immobilization pH region for all heavy metals tested, and significantly improves the stress-strain properties of the treated solids, thus allowing their reuse as readily available construction materials. The only potential problem associated with this quicklime/fly ash treatment is the excessive formation of the pozzolanic product ettringite in the presence of sulfates. Ettringite, when brought in contact with water, may cause significant swelling and subsequent deterioration of the stabilized matrix. Addition of minimum amounts of barium hydroxide was shown to effectively eliminate ettringite formation.
- Research Organization:
- North Dakota Univ., Grand Forks, ND (United States)
- OSTI ID:
- 374625
- Report Number(s):
- DOE/MC/30097--5161-Pt.2; CONF-9410458--Pt.2; ON: DE96011553
- Country of Publication:
- United States
- Language:
- English
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