The Effect of Soil Type on the Electrodialytic Remediation of Lead-Contaminated Soil

Abstract

This work investigates the influence of soil type on electrodialytic remediation (EDR) of lead (Pb). In electrokinetic soil remediation, it is well known that pH is a key factor and that carbonate influences remediation efficiency negatively. This work provides results from laboratory-scale EDR experiments with ten representative industrially Pb-contaminated surface soils. Results indicate that Pb speciation is of primary importance. Specifically, organic matter and stable compounds like PbCrO4 can impede and possibly even preclude soil remediation. In soils rich in carbonate, where the acidic front is impeded, part of the Pb can be transferred from the soil to the anolyte as negatively charged complexes during the EDR process. In this case the dominant complex is likely to be Pb(CO₃)₂²⁻. Efficient remediation is however not obtained until all carbonate has dissolved and Pb²⁺ is transported to the catholyte. Thus, the presence of carbonate negatively influences the remediation time. Pb bound to soluble organic matter is also transported toward the anolyte during EDR. The primary effect of the mainly insoluble organic matter commonly present in surface soil is however to immobilize Pb and impede remediation. Overall, EDR remediation of fine-grained, inorganic soils is found to be feasible when the Pb is not associated with extremely stable compounds.