Sorption isotherm-sequential extraction analysis of heavy metal retention in landfill liners

The chemical partitioning of heavy metals in soil materials is of great importance in risk assessment, landfill bottom liner design, and remedial investigation. The sorption characteristics of clayey calcareous sediments used to construct landfill bottom liners at four sites in southeastern Michigan were studied using a new method: combined sequential extraction-sorption isotherm analysis (CSSA). After spiking to simulate high levels of contamination, the sediments sorbed large quantities of Pb (similar to 1480-145 000 mg kg(-1)), Ni (similar to 750-8100 mg kg(-1)), and Cd (similar to 980-5070 mg kg(-1)). Sequential extraction data indicated that Pb and Ni were principally in a carbonate-occluded form, whereas Cd was mainly in an exchangeable form at high levels (>1000 mg kg(-1)) of contamination. These results suggest that Pb and Ni will be immobilized by the Liner materials but Cd will probably be highly mobile. By applying sequential extraction analysis after spiking, Langmuir sorption isotherms were constructed successfully for most of the individually targeted phases. Thus, CSSA appears to be a promising method for predicting the attenuation capabilities of soils and sediments because it allows the sorption capacities of individual phases to be determined while together in a natural system.