Mechanisms of lead immobilization in treated soils
D. Dermatas, N. Menounou and X.G. Meng

We investigated the leachability and immobilization mechanisms of lead in quicklime- and quick-lime–fly-ash-treated artificial soils and lead-contaminated field soils. Artificially prepared clay–sand mixtures with two different types of clays at different clay–sand ratios enabled us to investigate min
eralogical and surface area effects. Batch extraction results indicate that Pb leachability in the 
montmorillonite–sand mixtures was much lower than in the kaolinite–sand mixtures. The effective
ness of the lime-based treatment was tested with different extraction tests and was compared to 
other effective immobilization techniques such as cement- and phosphate-based systems. The pH affects lead immobilization, and the apparent pH range of immobilization increases with increasing surface area (addition of fly ash). Lead immobilization was caused either by precipitation, adsorption,
or chemical inclusion. However, the solubility of possible Pb precipitates (e.g. carbonate, sulphates, etc.), is much higher than the leachable Pb from both artificial and natural soils. Moreover, chemical extraction at pH 4 showed that much of the Pb is not adsorbed, while quicklime–fly-ash treatment in
the artificial soils converted more than 70% of the total Pb to a strongly immobilized form. Therefore, the mechanism controlling the immobilization of Pb in lime-treated contaminated soils seems to be chemical inclusion in the newly formed pozzolanic products.

Key words: contamination, fly ash, immobilization, leaching, lead, lime, mechanisms, soil, stabilization, TCLP

Land Contamination & Reclamation, 14 (1), 43-56

DOI 10.2462/09670513.702

© 2007 EPP Publications Ltd

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