Flow-through sequential extraction approach developed from a batch extraction method.

Sequential extractions of contaminants from a soil or sediment have been shown to be cost-effective contaminated site assessment tools that provide information on contaminant partitioning within an environmental matrix. Such information is necessary for defining remediation alternatives and mitigation strategies. The typical sequential extraction approach involves a batch method, and known limitations include the possibility of contaminant readsorption to the remaining soil or sediment In this work, a flow-through reactor was constructed and tested for application in a sequential extraction scheme. The sequential extraction scheme used was one developed for actinide-contaminated materials. The flow-through approach gave partitioning results that were similar to the batch method for uranium. We also monitored the extraction of stable Ca, K, Fe, Al, Zr, and Sc and obtained partitioning results generally similar to those observed with the batch extraction, except for Ca. Our results indicate readsorption of Ca when using a batch approach is small but significant and is eliminated with our new flow-through method. A limitation of the flow-through method is the possibility of underextraction of certain phases and higher analytical uncertainties. These uncertainties are more difficult to minimize, as compared to the uncertainty obtained with a batch approach.