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Pb speciation versus TCLP release in army firing range soils
D Dermatas1, G Shen, M Chrysochoou
1WM Keck Geoenvironmental Laboratory, Center for Environmental Systems, Stevens Institute of Technology, Hoboken, NJ 07030, USA.
Journal of Hazardous Materials
|January 3, 2006
Summary
Lead speciation in firing range soils is primarily controlled by lead carbonate precipitation and dissolution, influenced by pH and carbonate availability. Geochemical modeling offers a reliable assessment of lead leaching, surpassing traditional sequential extraction tests.
Area of Science:
- Environmental Science
- Soil Science
- Geochemistry
Background:
- Lead (Pb) contamination in US Army firing range soils poses environmental risks.
- Understanding lead speciation and mobility is crucial for risk assessment.
- Existing methods for assessing lead leachability have limitations.
Purpose of the Study:
- To investigate lead speciation and leaching behavior in firing range soils.
- To compare the effectiveness of different analytical techniques for lead assessment.
- To evaluate the role of geochemical modeling in predicting lead mobility.
Main Methods:
- Soil characterization: gradation, total chemical analysis, X-ray powder diffraction (XRPD), Rietveld quantification, optical microscopy, scanning electron microscopy (SEM).
- Leachability assessment: Toxicity Characteristic Leaching Procedure (TCLP) and Sequential Extraction Test (SET).
- Geochemical modeling using Visual MINTEQ.
Main Results:
- Lead retention mechanisms include lead carbonate precipitation and sorption in fine-grained soils.
- TCLP concentrations did not always correlate with total lead; leachability depends on soil mineralogy and pH.
- Geochemical modeling indicated lead carbonate precipitation/dissolution controls TCLP leachability, with pH, available lead, and carbonate as key factors.
- Sequential Extraction Tests (SET) can be unreliable due to carbonation reactions.
Conclusions:
- Geochemical modeling is a valuable tool for assessing lead speciation and environmental risks in firing range soils.
- Lead carbonate precipitation/dissolution is the dominant mechanism controlling lead leachability.
- A comprehensive approach combining geotechnical, mineralogical, chemical analyses, and geochemical modeling is recommended for accurate lead assessment.
