Heavy metal contaminants removal by soil washing

Abstract

The feasibility of soil washing for decontaminating a silty sand spiked with cadmium, chromium, lead, and zinc was evaluated in laboratory-scale batch and column experiments. Soil samples were subjected to chelant extraction using a solution of disodium salt of ethylenediaminetetraacetic acid (Na 2EDTA), sodium metabisulfite (Na 2S 2O 5) solution (an inexpensive reducing reagent), and a solution containing a mixture of the two reagents. Batch and column washing of the contaminated soil with deionized water (DI water) revealed that ≈70% of the cadmium in the sample is weakly bound and readily mobilized in aqueous solution at neutral pH, followed by ≈25%–30% of zinc, ≈20%–25% chromium, and only ≈10% of lead. Of the washing reagents tested, Na 2EDTA solutions were generally more effective than Na 2S 2O 5 for removing heavy metals from the soil samples. Na 2EDTA preferentially extracted lead over zinc and cadmium but exhibited little impact on chromium removal. Cadmium and, especially zinc, removal by a 0.01-M Na 2EDTA solution were enhanced considerably by inclusion of 0.1 M Na 2S 2O 5, suggesting that a mixture of the two reagents may provide an economically optimum solution for certain contaminated soils.